Metagenomic analysis of intestinal microbial function and key genes responsive to acute high-salinity stress in Nile tilapia (Oreochromis niloticus)

The intestinal microbiota is increasingly recognized as playing an important role in aquatic animals. To investigate the functional roles and mechanisms of the intestinal microbial genes/enzymes responding to salinity stress or osmotic pressure in fish, metagenomic analysis was carried out to evaluate the response of intestinal microbiota and especially their functional genes/enzymes from freshwater (the control group) to acute high salinity stress (the treatment group) in Nile tilapia. Our results showed that at the microbial community level, the intestinal microbiota in Nile tilapia generally underwent significant changes in diversity after acute high salinity stress. Among them, the shift in the bacterial community (mainly from Actinobacteria to Proteobacteria) dominated and had a large impact, the fungal community showed a very limited response, and other microbiota, such as phages, likely had a negligible response. At the functional level, the intestinal bacteriadecreased the normal physiological demand and processes, such as those of the digestive system and nervous system, but enhanced energy metabolism. Furthermore, at the gene level, some gene biomarkers, such as glutathione S-transferase, myo-inositol-1(or 4)-monophosphatase, glycine betaine/proline transport system permease protein, and some families of carbohydrate-active enzymes (GT4, GT2), were significantly enriched. However, GH15, GH23 and so on were significantly reduced. Exploring the functional details of the intestinal microbial genes/enzymes that respond to salinity stress in Nile tilapia sheds light on the mechanism of action of the intestinal microbiota with respect to the salinity adaptation of fish.

Effects of dietary garlic (Allium sativum) oil on growth performance, haemato-biochemical and histopathology of cypermethrin-intoxicated Nile tilapia (Oreochromis niloticus)

BACKGROUND

When pesticides are introduced into wetlands by agriculture, fish quickly absorb them through their gills. Pesticides reduce hatchability, impede growth, and antioxidant response, killing fish. Therefore, it's crucial to find effective pesticide mitigation methods for fish.

OBJECTIVE

In this study, the effects of garlic (Allium sativum) oil on the growth, haematology, biochemistry and histopathology parameters of Nile tilapia (Oreochromis niloticus) exposed to cypermethrin toxicity were investigated.

METHODS

In the research, cypermethrin was added to the water of the experimental groups at a rate of 1:20 of the LC50 value, and 1.00% garlic oil was added to the fish feed. Fish with an initial weight of 30.26 ± 0.26 g were fed for 45 days.

RESULTS

At the end of feeding, the final weights were determined as 69.39 ± 0.41 (G1), 61.81 ± 0.65 (G2), 82.25 ± 0.36 (G3), and 75.04 ± 0.68 (G4) grams, respectively. Histopathological examinations revealed serious lesions in the gill, liver, brain, and muscle tissues in the cypermethrin group, whereas these lesions were minimal or absent in the garlic oil group.

CONCLUSIONS

Garlic oil supplementation had positive effects on growth, haematology, blood biochemistry, hepatosomatic index and histopathological parameters. These findings suggest that garlic oil is a potential protective agent against cypermethrin toxicity.

Polystyrene nanoplastic and engine oil synergistically intensify toxicity in Nile tilapia, Oreochromis niloticus : Polystyrene nanoplastic and engine oil toxicity in Nile tilapia

Polystyrene nanoplastic (PS-NPs) and Engine oil (EO) pose multiple ecotoxic effects with increasing threat to fish ecosystems. The current study investigated the toxicity of 15 days exposure to PS-NPs and / or EO to explore their combined synergistic effects on Nile tilapia, Oreochromis niloticus (O. niloticus). Hematobiochemical parameters, proinflammatory cytokines, and oxidative stress biomarkers as well as histological alterations were evaluated. The experimental design contained 120 acclimated Nile tilapia distributed into four groups, control, PS-NPs (5 mg/L), EO (1%) and their combination (PS-NPs + EO). After 15-days of exposure, blood and tissue samples were collected from all fish experimental groups. Results indicated that Nile tilapia exposed to PS-NPs and / or EO revealed a significant decrease in almost all the measured hematological parameters in comparison to the control, whereas WBCs and lymphocyte counts were significantly increased in the combined group only. Results clarified that the combined PS-NPs + EO group showed the maximum decrease in RBCs, Hb, MCH and MCHC, and showed the maximum significant rise in interleukin-1β (IL-1β), and interleukin-6 (IL-6) in comparison to all other exposed groups. Meanwhile, total antioxidant capacity (TAC) showed a significant (p < 0.05) decline only in the combination group, whereas reduced glutathione (GSH) showed a significant decline in all exposed groups in comparison to the control. Both malondialdehyde (MDA) and aspartate aminotransferase (AST) showed a significant elevation only in the combination group. Uric acid showed the maximum elevation in the combination group than all other groups, whereas creatinine showed significant elevation in the EO and combination group when compared to the control. Furthermore, the present experiment proved that exposure to these toxicants either individually or in combination is accompanied by pronounced histomorpholgical damage characterized by severe necrosis and hemorrhage of the vital organs of Nile tilapia, additionally extensively inflammatory conditions with leucocytes infiltration. We concluded that combination exposure to both PS-NPs and EO caused severe anemia, extreme inflammatory response, oxidative stress, and lipid peroxidation effects, thus they can synergize with each other to intensify toxicity in fish.

Combined effects of ammonia-N exposure and salinity changes on hematological and serum biochemical factors and thyroid hormones in Nile tilapia (Oreochromis niloticus)

The aim of this research was to evaluate the interaction effects of ammonia-N levels and salinity on hematological and serum biochemical parameters in Nile tilapia (Oreochromis niloticus). The fish were randomly divided into 12 treatments including the levels of salinity (0, 4, 8 and 12 ppt) and 0, 50% of LC50-96 h of ammonia-N and 30% of LC50-96 h of ammonia-N in a factorial design (4 salinity levels x 3 ammonia levels). Hemoglobin value in all treatments, except for salinity treatments, namely 2, 3, 4, showed a significant decrease than the control (0 ppt and no poisoning). Also, red blood cells in treatment ammonia-N levels were significantly less than the control. Serum protein concentration, in treatments 9 (50% of LC50-96 h of ammonia-N) and 5 and also with increasing salinity (treatments 2, 3 and 4) had a significant decrease compared to the control. There is a significant increase in serum glucose, cortisol, ammonia and urea levels in 50% and 30% of LC50-96 h of ammonia-N treatments compared to the control, meanwhile these parameters were significantly increased with increasing salinity. Serum thyroid stimulating hormone (TSH), T3 and T4 levels in acute and sub-acute ammonia-N treatments were significantly lower than the control. Moreover, with increasing salinity in 50% and 30% of LC50-96 h of ammonia-N treatments, TSH showed a decreasing pattern. According to the results, fluctuations in blood biochemical factors, increase of stress and decrease of thyroid hormones show that the salinity, ammonia, and their interaction caused adverse effects on fish health during the 96 h of testing.

Study on the osmotic response and function of myo-inositol oxygenase in euryhaline fish nile tilapia (Oreochromis niloticus)

To understand the role of myo-inositol oxygenase (miox) in the osmotic regulation of Nile tilapia, its expression was analyzed in various tissues. The results showed that the expression of miox gene was highest in the kidney, followed by the liver, and was significantly upregulated in the kidney and liver under 1 h hyperosmotic stress. The relative luminescence efficiency of the miox gene transcription starting site (-4,617 to +312 bp) under hyperosmotic stress was measured. Two fragments (-1,640/-1,619 and -620/-599) could induce the luminescence activity. Moreover, the -1,640/-1,619 and -620/-599 responded to hyperosmotic stress and high-glucose stimulation by base mutation, suggesting that osmotic and carbohydrate response elements may exist in this region. Finally, the salinity tolerance of Nile tilapia was significantly reduced after the knocking down of miox gene. The accumulation of myo-inositol was affected, and the expression of enzymes in glucose metabolism was significantly reduced after the miox gene was knocked down. Furthermore, hyperosmotic stress can cause oxidative stress, and MIOX may help maintain the cell redox balance under hyperosmotic stress. In summary, MIOX is essential in osmotic regulation to enhance the salinity tolerance of Nile tilapia by affecting myo-inositol accumulation, glucose metabolism, and antioxidant performance.NEW & NOTEWORTHY Myo-inositol oxygenase (MIOX) is the rate-limiting enzyme that catalyzes the first step of MI metabolism and determines MI content in aquatic animals. To understand the role of miox in the osmotic regulation of Nile tilapia, we analyzed its expression in different tissues and its function under hyperosmotic stress. This study showed that miox is essential in osmotic regulation to enhance the salinity tolerance of Nile tilapia by affecting myo-inositol accumulation, glucose metabolism, and antioxidant performance.

Establishing a safe anesthesia concentration window for Nile tilapia (Oreochromis niloticus) (Linnaeus 1758) by monitoring cardiac activity in eugenol immersion baths

Nile tilapia, Oreochromis niloticus, is the most cultivated fish species in the world, due to its low cost, high growth rate, environmental adaptability, and resistance to disease and stress. Anesthetics for fish become necessary in management because they minimize mortality during transport and maintenance of ponds, one of the most used anesthetics is clove oil, which has eugenol as the major substance, representing 90-95 % of clove oil. The present study evaluates the effect of eugenol on cardiac activity in Oreochromis niloticus specimens and relates it to behavioral data to determine a concentration window for safe anesthesia. For the comportamental analysis, was used five treatments (50, 75, 100, 125, and 150 μL·L-1) were evaluated and for the eletrocardiographic test was used seven groups (Control, Vehicle, 50, 75, 100, 125, and 150 μL·L-1), n = 9/treatment, totaling 108 animals. Behavioral and electrocardiographic tests were performed on all treatments during induction and recovery. The results of the behavioral tests demonstrated the reversibility of the effects with recovery of the posture reflex, varying according to the concentration. The ECG results showed a slow recovery because, at concentrations above 100 μL·L-1, there was no full reversibility of the cardiac effects in the observed experiment time, which could cause greater changes in the tilapia hemodynamics, which led us to identify a window for safe anesthesia. Eugenol is an effective anesthetic in Nile tilapia juveniles when used in concentrations ranging from 50 to 100 μL·L-1, if there is a need for anesthetic deepening, doses above 100 μL·L-1, however, the animals must be monitored due to hemodynamic changes.

Implications of deltamethrin on hematology, cardiac pathology, and gene expression in Nile tilapia (Oreochromis niloticus) and its possible amelioration with Shatavari (Asparagus racemosus)

Deltamethrin (DM) is one of the extensively used pyrethroids for controlling ectoparasites. Unfortunately, DM is highly toxic to fish as it primarily targets the sodium channels of the plasma membrane thereby affecting their cardiac and nervous systems. The present study investigated the protective efficacy of Shatavari (Asparagus racemosus) against DM-induced cardiotoxicity in Nile tilapia (Oreochromis niloticus). The fish were segregated into nine groups having 36 fish/group maintained in triplicates exposed to DM (1 µg/L) and fed with a diet containing three different concentrations (10 g, 20 g, and 30 g/kg feed) of aqueous extract of A. racemosus (ARE) for 21 days. DM caused significant alterations in the blood and serum parameters, and expression of cardiac and apoptotic genes compared to the control group. The ARE cotreatment significantly reduced the increase in serum transaminases, creatine kinase, and lactate dehydrogenase levels induced by DM. ARE facilitated the regain of electrolyte (sodium, potassium, chloride) homeostasis and antioxidants such as catalase, superoxide dismutase, glutathione peroxidase, and glutathione in DM-exposed fish. The cardiac histology exhibited loose separation of the cardiomyocytes and myofibrillar loss in the DM group which was ameliorated in the DM-ARE cotreatment group. Significant modulations were observed in the expression of cardiac-specific genes (gata4, myh6, tnT, cox1) and apoptosis signaling genes and proteins (HSP70, bax, bcl-2, caspase3), in the cotreatment group compared to the DM-exposed group. The current study suggests that ARE possesses potential cardioprotective properties that are effective in mitigating the toxic effects induced by DM via ameliorating oxidative stress, electrolyte imbalance, and apoptosis in tilapia.

Modulatory effects of dietary prickly pear (Opuntia ficus-indica) peel on high salinity tolerance, growth rate, immunity and antioxidant capacity of Nile tilapia (Oreochromis niloticus)

This study evaluated the effects of prickly pear (Opuntia ficus-indica) peel (PPP) on salinity tolerance, growth, feed utilization, digestive enzymes, antioxidant capacity, and immunity of Nile tilapia (Oreochromis niloticus). PPP was incorporated into four iso-nitrogenous (280 g kg-1 protein) and iso-energetic (18.62 MJ kg-1) diets at 0 (PPP0), 1 (PPP1), 2 (PPP2), and 4 (PPP4) g kg-1. Fish (9.69 ± 0.2 g) (mean ± SD) were fed the diets for 75 days. Following the feeding experiment, fish were exposed to a salinity challenge (25‰) for 24 h. Fish survival was not affected by the dietary PPP inclusion either before or after the salinity challenge. Fish fed the PPP-supplemented diets showed lower aspartate aminotransferase, alanine aminotransferase, cortisol, and glucose levels compared to PPP0, with the lowest values being observed in PPP1. Fish fed dietary PPP had higher growth rates and feed utilization than PPP0. Quadratic regression analysis revealed that the best weight gain was obtained at 2.13 g PPP kg-1 diet. The highest activities of protease and lipase enzymes were recorded in PPP1, while the best value of amylase was recorded in PPP2, and all PPP values were higher than PPP0. Similarly, PPP1 showed higher activities of lysozyme, alternative complement, phagocytic cells, respiratory burst, superoxide dismutase, glutathione peroxidase and catalase, and lower activity of malondialdehyde than in PPP0. Further increases in PPP levels above 2 g kg-1 diet led to significant retardation in the immune and antioxidant parameters. Thus, the inclusion of PPP at about 1 to or 2 g kg-1 diet can improve stress tolerance, immunity, and antioxidant capacity in Nile tilapia.

Genetic and morphological characterization of a new genotype of nervous necrosis virus circulating among Nile tilapia in the south of Egypt

Nervous necrosis virus (NNV) is the causative agent of viral nervous necrosis in freshwater and marine fishes. In this study, NNV circulating among wild and farmed Nile tilapia (Oreochromis niloticus) was genetically and morphologically characterized using reverse transcription polymerase chain reaction (RT-PCR), sequencing analysis, and transmission electron microscopy (TEM). Brain, eye, and other organ (spleen, kidney, heart, and liver) specimens were collected from 87 wild (66) and farmed (21) Nile tilapia fish during their adult or juvenile stage at different localities in Qena and Sohag governorates in southern Egypt. Among them, 57/87 fish showed suspected NNV clinical signs, and 30/87 were healthy. The results revealed that NNV was detected in 66 out of 87 fish (58.62% in the wild and 17.24% in farmed Nile tilapia by RT-PCR), and the prevalence was higher among diseased (55.17%) than in healthy (20.69%) fish. NNV was detected in the brain, eye, and other organs. Using TEM, virion size variations based on the infected organs were observed. Nucleotide sequence similarity indicated that NNVs had a divergence of 75% from other fish nodaviruses sequenced in Egypt and worldwide. Phylogenetic analysis distinguished them from other NNV genotypes, revealing the emergence of a new NNV genotype in southern Egypt. In conclusion, NNV is circulating among diseased and healthy Nile tilapia, and a new NNV genotype has emerged in southern Egypt.

Pseudomonas putida infection induces immune-antioxidant, hepato-renal, ethological, and histopathological/immunohistochemical disruptions in Oreochromis niloticus: the palliative role of titanium dioxide nanogel

BACKGROUND

Pseudomonas putida is a pathogenic bacterium that induces great losses in fishes, including Nile tilapia (Oreochromis niloticus). Currently, the application of nanomaterials in aquaculture practices has gained more success as it endows promising results in therapies compared to traditional protocols.

OBJECTIVE

Therefore, the current perspective is considered the first report to assess the anti-bacterial efficacy of titanium dioxide nanogel (TDNG) against Pseudomonas putida (P. putida) in Nile tilapia.

METHODS

The fish (n = 200; average body weight: 47.50±1.32 g) were allocated into four random groups (control, TDNG, P. putida, and TDNG + P. putida), where 0.9 mg/L of TDNG was applied as bath treatment for ten days.

RESULTS

Outcomes revealed that P. putida infection caused ethological alterations (surfacing, abnormal movement, and aggression) and depression of immune-antioxidant variables (complement 3, lysozyme activity, total antioxidant capacity, superoxide dismutase, and reduced glutathione content). Additionally, a substantial elevation in hepatorenal biomarkers (aspartate and alanine aminotransferases and creatinine) with clear histopathological changes and immuno-histochemical alterations (very weak BCL-2 and potent caspase-3 immuno-expressions) were seen. Surprisingly, treating P. putida-infected fish with TDNG improved these variables and obvious restoration of the tissue architectures.

CONCLUSION

Overall, this report encompasses the key role of TDNG as an anti-bacterial agent for controlling P. putida infection and improving the health status of Nile tilapia.

Comparative pathogenicity of Nocardia seriolae in Nile tilapia (Oreochromis niloticus), milkfish (Chanos chanos) and Asian seabass (Lates calcarifer)

Nocardiosis, caused by Nocardia seriolae, has been a prominent disease in Southeast Asian aquaculture in the last three decades. This granulomatous disease reported in various fish species is responsible for significant economic losses. This study investigated the pathogenicity of N. seriolae in three cultured species in Taiwan: Nile tilapia (omnivore), milkfish (herbivore) and Asian seabass (carnivore). Administration of an infective dose of 1 × 106 CFU/ fish in tilapia, seabass and milkfish demonstrated mortalities of 100%, 90% and 75%, respectively. Additionally, clinical signs namely, granuloma and lesions displayed varying intensities between the groups and pathological scores. Polymerase chain reaction (PCR) amplification specific for N. seriolae was confirmed to be positive (432 bp) using NS1/NG1 primers. Post-mortem lesions revealed the absence of granulomas in tilapia and milkfish and their presence in the seabass. Interestingly, the gut in tilapia showed an influx of eosinophils suggesting its role during the acute stages of infection. However, post-challenge, surviving milkfish exhibited granulomatous formations, while surviving seabass progressed toward healing and tissue repair within sampled tissues. Overall, in conclusion, these results demonstrate the versatility in the immunological ability of individual Perciformes to contain this pathogen as a crucial factor that influences its degree of susceptibility.

The Potential of Fish Protein Hydrolysate Supplementation in Nile Tilapia Diets: Effects on Growth and Health Performance, Disease Resistance, and Farm Economic Analysis

Fish protein hydrolysate (FPH) has shown immense potential as a dietary protein supplement and immunostimulant in aquaculture, especially in Nile tilapia production. Four isoproteic diets (30% crude protein) were prepared by including FPH at varying percentages (0%, 0.5%, 1%, and 2%). Nile tilapia fed with FPH diets for 90 days, and their growth performance, feed utilization, blood biochemistry, liver and gut morphology, and resistance against Streptococcus iniae were investigated. The findings revealed that diets physical attributes such as pellet durability index and water stability were remarkably (p < 0.05) varied between experimental diet groups. Furthermore, the test diets were more palatable when FPH was included at 1% and 2%. Fish that were fed with a 2% FPH-treated diet had significantly (p < 0.05) greater growth indices than other treatments. Additionally, their feed utilization was significantly (p < 0.05) improved. The experimental diets and intestinal total bacteria count (TBC) exhibited a rising trend with FPH levels, where the 2% FPH-treated diet recorded the highest TBC. Neutrophil (109/L), lymphocyte (109/L), eosinophil (109/L), and red blood cell(1012/L) counts were significantly (p < 0.05) higher in the 2% FPH-treated group, while the white blood cell (109/L), and basophil (109/L) counts were not influenced by the FPH inclusion. Moreover, the FPH-treated groups displayed lower creatinine, bilirubin, and urea levels than the control. The histological examination demonstrated that themid-intestine of 2% FPH-fed Nile tilapia had an unbroken epithelial wall, more villi with frequent distribution of goblet cells, wider tunica muscularis, and stronger stratum compactum bonding than other treatments. Additionally, this group exhibited more nuclei and erythrocytes and less vacuolar cytoplasm in liver than their counterparts. Nile tilapia that were given a diet containing 2% FPH had significantly (p < 0.05) higher resistance (83.33%) to S. iniae during the bacterial challenge test. A significant (p < 0.05) enhancement in farm economic efficiency was observed in the higher inclusion of FPH in diets. In summary, 2% FPH supplementation in Nile tilapia diets improved their growth performance, feed utilization, health status, disease resistance, and farm economic efficiency.

Ontogeny and tissue specific expression profiles of recombination activating genes (RAGs) during development in Nile tilapia, Oreochromisniloticus

Recombination activating genes (RAGs) mediates the process of rearrangement and somatic recombination (V(D)J) to generate different antibody repertoire. Studies on the expression pattern of adaptive immune genes during ontogenic development are crucial for the formulation of fish immunization strategy. In the present study, Nile tilapia was taken to explore the relative expression profile of RAG genes during their developmental stages. The developmental stages of Nile tilapia, i.e., unfertilized egg, 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28 and 30 days post-hatch (dph) and kidney, blood, gill, liver and spleen tissues from adult fish were collected and the cDNA synthesis was carried out. Gene specific primers for RAG-1 and RAG-2 of Nile tilapia were designed and their annealing temperature (Tm) was optimized by gradient PCR. Consequently, PCR was performed to confirm the specific amplification of RAG-1 and RAG-2 genes. Quantitative real-time PCR (qRT-PCR) gene expression of RAG-1 and RAG-2 were noticed in all the developmental stages; however, a significant increase was observed after 12 dph and peaked at 24 dph, followed by a gradual decrease until 30 dph. Tissue-specific gene expression profiling revealed that the highest expression of RAG-1 and RAG-2 was observed in the kidney, followed by spleen, gill, liver and blood. The findings of the study explored the suitable timing of lymphoid maturation that could be technically used for the adoption of strategies to improve disease resistance of fish larvae for mitigating larval mortality.

A novel study of brain microvascular endothelial cells induced by astrocyte conditioned medium for constructing blood brain barrier model in vitro: A promising tool for meningitis of teleost

The blood-brain barrier (BBB) is mainly composed of specialized endothelial cells, which can resist harmful substances, transport nutrients, and maintain the stability of the brain environment. In this study, an endothelial cell line from tilapia (Oreochromis niloticus) named TVEC-01 was successfully established. During the earlier establishment phase of the cell line, the TVEC-01 cells were persistently exposed to an astrocyte-conditioned medium (ACM). TVEC-01 cells were identified as an endothelial cell line. TVEC-01 cells retained the multiple functions of endothelial cells and were capable of performing various experiments in vitro. Furthermore, TVEC-01 cells efficiently expressed BBB-related tight junctions and key efflux transporters. From the results of the qRT-PCR, we found that the TVEC-01 cell line did not gradually lose BBB characteristics after persistent and repetitive passages, which was different from the vast majority of immortalized endothelial cells. The results showed that ACM induced up-regulation of the expression levels of multiple BBB-related genes in TVEC-01 cells. We confirmed that Streptococcus agalactiae was capable of invading the TVEC-01 cells and initiating a series of immune responses, which provided a theoretical basis for S. agalactiae to break through the BBB of teleost through the transcellular traversal pathway. In summary, we have successfully constructed an endothelial cell line of teleost, named TVEC-01, which can be used in many experiments in vitro and even for constructing BBB in vitro. Moreover, it was confirmed that S. agalactiae broke through the BBB of teleost through the transcellular traversal pathway and caused meningitis.

Safety, tolerability and biological responses of Oreochromis niloticus juveniles upon oral oxolinic acid administration

In aquaculture, oxolinic acid (OA) is used as a second-line treatment at 12 mg/kg biomass/day for seven consecutive days. The present study evaluated the biosafety of 21 days of dietary administration of OA at 0, 12, 36, 60 and 120 mg by assessing the growth, biochemical, erythrocytic morphological and histopathological alterations and residue levels in Oreochromis niloticus. A significant dose-dependent reduction in feed intake and biomass and an increase in mortalities and erythrocytic cellular and nuclear changes were recorded. Significant elevations in plasma glucose, creatinine, alkaline phosphatase, alanine transaminase and aspartate transaminase and a decline in calcium and chloride levels were documented. The kidney, liver and intestine histoarchitecture showed mild to marked alterations. The edible tissue OA residues peaked on day 21 and decreased upon cessation of administration in all the dosing groups. The residue levels in the muscle of the recommended dose group were well within the maximum residue limit set by the European Medicines Evaluation Agency. Although the current study hinted at the safety and tolerability of OA even during long-term usage in O. niloticus in Indian conditions, care must be exercised for its aquacultural application because of its listing as a critically important medicine for humans.

A CD6 homolog of Nile tilapia (Oreochromis niloticus) conserved binding bacteria involved in the regulation of Streptococcus agalactiae induced inflammation

As a lymphocyte-specific surface receptor belonging to the cysteine-rich superfamily of scavenger receptors, CD6 acts as a pattern recognition receptor for microbial components and is involved in the regulation of inflammatory responses. However, the characteristics and functions of CD6 molecules in lower vertebrates represented by teleost fish are unknown. In this study, a CD6 homolog (designated OnCD6) was characterized from Nile tilapia (Oreochromis niloticus), and establishing its role as a PRRs that participates in immune recognition. OnCD6 contains an open reading frame of 1872 bp that encodes a peptide of 623 amino acids, and contains two conserved SR domain. Multiple sequence alignment revealed that OnCD6 shares a relatively high level of identity with those of other species. Transcriptional expression analysis revealed that OnCD6 was constitutively expressed in immunes tissues such as head kidney and thymus. The expression level of OnCD6 in mainly immune tissues were found significantly upregulated after the injection of Streptococcus agalactiae (S. agalactiae). Moreover, OnCD6 protein was located in the head kidney and brain, mainly over the plasma membrane of lymphocytes in these immune tissues. In vitro experiments showed that CD6 extracellular protein bound to and aggregated several Gram-positive and -negative bacterial strains through the recognition of bacterial surface conserved components LPS and LTA etc. In vivo experiments demonstrated that overexpression OnCD6 before S. agalactiae challenge significantly improved tilapia survival, and this was concomitant with reduced bacterial load and pro-inflammatory cytokines (IL-1β and TNF-α). Taken together, our results illustrated the function of CD6 molecular pattern recognition receptors (PRRs) is conserved and plays an important role in antibacterial infection.

Longitudinal Survey of Aeromonas hydrophila and Foodborne Pathogens in a Commercial Aquaponics System

Aquaponic production of fresh produce is a sustainable agricultural method becoming widely adopted, though few studies have investigated potential food safety hazards within commercial systems. A longitudinal study was conducted to isolate and quantify several foodborne pathogens from a commercial, aquaponic farm, and to elucidate their distribution throughout. The survey was conducted over 2 years on a controlled-environment farm containing Nile tilapia (Oreochromis niloticus) and lettuce (Lactuca sativa). Samples (N = 1,047) were collected bimonthly from three identical, independent systems, and included lettuce leaves, roots, fingerlings (7-126 d old), feces from mature fish (>126 d old), water, and sponge swabs collected from the tank interior surface. Most probable number of generic Escherichia coli were determined using IDEXX Colilert Quanti-Tray. Enumeration and enrichment were used to detect Shiga toxin-producing E. coli (STEC), Salmonella enterica, Listeria monocytogenes, Aeromonas spp., Aeromonas hydrophilia, and Pseudomonas aeruginosa. Generic E. coli, STEC, L. monocytogenes, and S. enterica were not detected in collected samples. P. aeruginosa was isolated from water (7/351; 1.99%), swabs (3/351; 0.85%), feces (2/108; 1.85%), and lettuce leaves (2/99; 2.02%). A. hydrophila was isolated from all sample types (623/1047; 59.50%). The incidence of A. hydrophila in water (X2 = 23.234, p < 0.001) and sponge samples (X2 = 21.352, p < 0.001) increased over time.

Evaluate the potential use of TonB-dependent receptor protein as a subunit vaccine against Aeromonas veronii infection in Nile tilapia (Oreochromis niloticus)

Aeromonas veronii is an emerging bacterial pathogen that causes serious systemic infections in cultured Nile tilapia (Oreochromis niloticus), leading to massive deaths. Therefore, there is an urgent need to identify effective vaccine candidates to control the spread of this emerging disease. TonB-dependent receptor (Tdr) of A. veronii, which plays a role in the virulence factor of the organism, could be useful in terms of protective antigens for vaccine development. This study aims to evaluate the potential use of Tdr protein as a novel subunit vaccine against A. veronii infection in Nile tilapia. The Tdr gene from A. veronii was cloned into the pET28b expression vector, and the recombinant protein was subsequently produced in Escherichia coli strain BL21 (DE3). Tdr was expressed as an insoluble protein and purified by affinity chromatography. Antigenicity test indicated that this protein was recognized by serum from A. veronii infected fish. When Nile tilapia were immunized with the Tdr protein, specific antibody levels increased significantly (p-value <0.05) at 7 days post-immunization (dpi), and peaked at 21 dpi compared to antibody levels at 0 dpi. Furthermore, bacterial agglutination activity was observed in the fish serum immunized with the Tdr protein, indicating that specific antibodies in the serum can detect Tdr on the bacterial cell surface. These results suggest that Tdr protein has potential as a vaccine candidate. However, challenging tests with A.veronii in Nile tilapia needs to be investigated to thoroughly evaluate its protective efficacy for future applications.

Collectin-K1 Plays a Role in the Clearance of Streptococcus agalactiae in Nile Tilapia (Oreochromis niloticus)

Collectin-K1 (CL-K1) is a multifunctional C-type lectin that has been identified as playing a crucial role in innate immunity. It can bind to carbohydrates on pathogens, leading to direct neutralization, agglutination, and/or opsonization, thereby inhibiting pathogenic infection. In this study, we investigated a homolog of CL-K1 (OnCL-K1) in Nile tilapia (Oreochromis niloticus) and its role in promoting the clearance of the pathogen Streptococcus agalactiae (S. agalactiae) and enhancing the antibacterial ability of the fish. Our analysis of bacterial load displayed that OnCL-K1 substantially reduced the amount of S. agalactiae in tissues of the liver, spleen, anterior kidney, and brain in Nile tilapia. Furthermore, examination of tissue sections revealed that OnCL-K1 effectively alleviated tissue damage and inflammatory response in the liver, anterior kidney, spleen, and brain tissue of tilapia following S. agalactiae infection. Additionally, OnCL-K1 was found to decrease the expression of the pro-inflammatory factor IL-6 and migration inhibitor MIF, while increasing the expression of anti-inflammatory factor IL-10 and chemokine IL-8 in the spleen, anterior kidney, and brain tissues of tilapia. Moreover, statistical analysis of survival rates demonstrated that OnCL-K1 significantly improved the survival rate of tilapia after infection, with a survival rate of 90%. Collectively, our findings suggest that OnCL-K1 plays a vital role in the innate immune defense of resisting bacterial infection in Nile tilapia. It promotes the removal of bacterial pathogens from the host, inhibits pathogen proliferation in vivo, reduces damage to host tissues caused by pathogens, and improves the survival rate of the host.

Effects of phytase enzyme supplementation on growth performance, intestinal morphology and metabolism in Nile tilapia (Oreochromis niloticus)

Phytase is crucial in enhancing the bioavailability and release of phosphorus and other nutrients bound to phytic acid, making them more bioavailable for animal absorption. This study was carried out to inspect the effect of supplementing low phosphorus (P) diet with di-calcium phosphate (DCP) and liquid phytase enzyme (LP), which contains 1500 FTU/kg, on growth performance, intestinal morphometry, proximate body chemical composition, blood profile, immunity status, liver mitochondrial enzyme activities, the expression response and economic returns of Nile tilapia (Oreochromis niloticus). Three triplicate groups of fish (initial weight 5.405 ± 0.045 g, N = 90) were fed on three different diets for 90 days. The first was a control diet with zero DCP; the second was a control diet supplemented with 0.71% DCP; the third was a control diet supplemented with 0.03% LP. The groups were designated as CG, DCP and LP, respectively. Results showed that LP induced considerable improvements (p < 0.05) in FBW, body weight gain, weight gain rate, specific growth rate, HIS, viscero-somatic index, spleen-somatic index, feed conversion ratio, blood parameters and the histomorphometry assessment of intestinal villi absorptive capacity, compared with the other groups. Also, whole-body protein and lipid contents pointedly (p < 0.05) increased by LP, compared with the DCP group. A positive response (p < 0.05) to the phytase enzyme was noted in complexes I, III and IV of the mitochondrial liver complex enzyme activity. Likewise, the relative gene expression levels of (GHr-1, IGF-1, FAS and LPL) were notably (p < 0.05) upregulated by phytase enzyme, associated with DCP and control groups. Further, phytase recorded the highest total return and profit percentage. It can be concluded that Nile tilapia benefits from using phytase enzyme 1500 FTU/kg at 0.03% without adding DCP in terms of good performance and profits.

Skin histopathological responses of Oreochromis niloticus (Nile tilapia) to transportation in water with and without salt

Oreochromis niloticus (Nile tilapia) is a well-known economic fish species that can thrive under the right environmental circumstances. The transport of live fish, either for food or as companion animals, presents a big issue for animal welfare at the same time it is considered one of stressful conditions. Hence, the present study investigated the skin histopathological responses of O. niloticus that were attributed to stress and salt addition during transportation. Three experimental groups of O. niloticus the 1st is the control non-transported group (CG), the 2nd is transport in water without salt (PT-S) and the 3rd is transport in water containing 5gL- 1salt (PT + S), the last 2 groups were transported in 5 h transport model. Results indicate that the skin of PT-S fish showed a marked decrease in epidermal thickness, decreased number of goblet cells, and an increase in the sub-epidermal and dermal pigments with the presence of large edematous vacuoles. Fish skin from PT + S demonstrated mild hydropic swelling in epidermal cells with normal goblet (mucous) cells density, and more or less normal melanin pigment distribution in sub epidermis and on the dermis layers, however, dermis showed mild edematous spaces. Scanning microscopy of PT-S skin tissue showed few scratched white patches among normal regions that may represent a thickened surface with the decreased number of goblets cell opening, while the PT + S group showed moderate preservation of surface skin architectures with the presence of goblet (mucous) cells opening in spite of presence of slight thickened white patches. The estimated total lesion changes present in PT-S group showed a significant increase (P < 0.001) compared with the control (CG) group. On the other hand, PT + S showed significant (P < 0.001) improvement in the overall previously recorded changes compared with the PT-S group, and a non- significant change in the histological architectures compared with the control group. Our findings underlined the importance of skin and its mucous cover health during transportation. The use 5 gL- 1salt during O. niloticus transportation appears to preserve the surface skin features, and keep the goblet (mucous) cells open to the external surface, and may act as a deterrent for the release of mucus from goblet (mucous) cells in response to stress and lessen the stress of transportation.

Effects of Dietary Tuber Ethanolic Extract of Nut Grass (Cyperus rotundus Linn.) on Growth, Immune Response, and Disease Resistance in Nile Tilapia (Oreochromis niloticus)

Nut grass (Cyperus rotundus Linn.) is a weed that grows in all tropical, subtropical and temperate regions of the world, including areas where it grows on saline soil. This research was conducted to evaluate the effect of C. rotundus tuber extract in the diet on the growth performance and disease resistance of Nile tilapia. Various components of phytochemical importance of nut grass, including sugars/carbohydrates, terpenoids, tannins, and flavonoids were found in C. rotundus. Tilapia (n = 25 fish/group in triplicate) were fed with different levels of nut grass extract including 0 (control; T1), 0.4 (T2), 0.8 (T3), and 1.6 (T4) g/kg for 60 days in a completely randomized design (CRD) experiment. After the feeding trial, the highest weight gain and average daily gain (ADG) were observed in the T4 group, but it was not significantly different from T3 (Nile tilapia fed with a 0.8 g/kg) (p > 0.05). The lowest feed conversion ratio (FCR) was observed in the T3 group. Moreover, the fillet, crud lipid content, and blood chemical profiles (aspartate aminotransferase (AST), cholesterol, and malondialdehyde (MDA)) in fish fed with 1.6 g/kg were highest when compared in all groups. In addition, the T3 group presented with the immune response parameter found in red blood cells (RBC), lysozyme activity, and antioxidant (superoxide dismutase activity (SOD)) being higher than those of the control group (p < 0.05). The highest survival (93.33%) was observed in fish fed with 0.8 g/kg (T3) after a 14 day challenge with Streptococcus agalactiae. Thus, it was concluded that nut grass extract at 0.8 g/kg can be used to improve the growth performance and the tendency for resistance to S. agalactiae in Nile tilapia.

Chlorella vulgaris extract conjugated magnetic iron nanoparticles in nile tilapia (Oreochromis niloticus): Growth promoting, immunostimulant and antioxidant role and combating against the synergistic infection with Ichthyophthirius multifiliis and Aeromonashydrophila

Nile tilapia reared under intensive conditions was more susceptible for Ichthyophthirius multifilii (I. multifiliis) infection eliciting higher mortality, lower productive rate and further bacterial coinfection with Aeromonas hydrophila (A. hydrophila). The higher potency of magnetic field of iron oxide nanoparticles (NPs) can kill pathogens through inhibiting their viability. Herein, coating of Chlorella vulgaris extract (ChVE) with magnetic iron oxide NPs (Mag iron NPs) can create an external magnetic field that facilitates their release inside the targeted tissues. Thus, the current study is focused on application of new functionalized properties of Mag iron NPs in combination with ChVE and their efficacy to alleviate I. multifiliis and subsequent infection with A. hydrophila in Nile tilapia. Four hundred fingerlings were divided into: control group (with no additives), three groups fed control diet supplemented with ChVE, Mag iron NPs and ChVE@Mag iron NPs for 90 days. At the end of feeding trial fish were challenged with I. multifiliis and at 9 days post challenge was coinfected by A. hydrophila. A remarkable higher growth rate and an improved feed conversion ratio were detected in group fed ChVE@Mag iron-NPs. The maximum expression of antioxidant enzymes in skin and gills tissues (GSH-Px, CAT, and SOD) which came in parallel with higher serum activities of these enzymes was identified in groups received ChVE@Mag iron-NPs. Furthermore, group fed a combination of ChVE and Mag iron-NPs showed a boosted immune response (higher lysozyme, IgM, ACH50, and MPO) prior to challenge with I. multifiliis. In contrast, fish fed ChVE@Mag iron-NPs supplemented diet had lower infection (decreased by 62%) and mortality rates (decreased by 84%), as well as less visible white spots (decreased by 92 % at 12 dpi) on the body surfaces and mucous score. Interestingly, post I. multifiliis the excessive inflammatory response in gill and skin tissues was subsided by feeding on ChVE@Mag iron-NPs as proved by down regulation of IL-1β, TNFα, COX-2 and iNOS and upregulation of IL-10, and IgM, IgT and Muc-2 genes. Notably, group exposed to I. multifiliis-showed higher mortality when exposed to Aeromonas hydrophilia (increased by 43 %) while group fed ChVE@Mag iron-NPs exhibited lower morality (2%). Moreover, the bacterial loads of A. hydrophilia in fish infected by I. multifiliis and fed control diet were higher than those received dietary supplement of ChVE, Mag iron-NPs and the most reduced load was obtained in group fed ChVE@Mag iron-NPs at 7 dpi. In conclusion, ChVE@Mag iron-NPs fed fish had stronger immune barrier and antioxidant functions of skin and gills, and better survival following I. multifiliis and A. hydrophilia infection.

Influence of dietary sodium taurocholate on the growth performance and liver health of Nile tilapia (Oreochromis niloticus)

Bile acids (BAs) are a class of cholesterol-derived amphipathic molecules approved as new animal feed additives. However, the functional researches mainly focused on BAs mixture, and the influence of the individual BA on fishes was still limited. In the present study, Nile tilapia were fed basal diet with three levels of sodium taurocholate at 0 mg/kg (CON), 300 mg/kg (TCAL), and 600 mg/kg (TCAH) for 8 weeks. The results indicated that addition of sodium taurocholate did not significantly influence the growth performance. Instead, TCAH group had higher cholesterol accumulation with liver fibrosis. In TCAH group, the level of nuclear factor E2-related factor 2 (nrf2) signaling-associated oxidative stress factors significantly increased in the liver. Additionally, fish in TCAH group had the highest expression level of genes encoding endoplasmic reticulum (ER) stress and inflammatory cytokines in the liver. In conclusion, 300 mg/kg of sodium taurocholate did not significantly influence the growth performance of fish, while 600 mg/kg of sodium taurocholate markedly induced cholesterol accumulation and liver injury, suggesting that the application of taurocholic acid in aquafeed should be re-evaluated.

Immune response and protective efficacy of Streptococcus agalactiae vaccine coated with chitosan oligosaccharide for different immunization strategy in nile tilapia (Oreochromis niloticus)

In the past decade, the outbreak of Streptococcus agalactiae has caused significant economic losses in tilapia farming. Vaccine immunization methods and strategies have gradually evolved from single-mode to multi-mode overall prevention and control strategies. In this study, an inactivated vaccine of S. agalactiae with a chitosan oligosaccharide (COS) adjuvant was constructed using different administration methods: intraperitoneal injection (Ip), immersion combined with intraperitoneal injection (Im + Ip), immersion combined with oral administration (Im + Or), and oral administration (Or). Safety analysis revealed no adverse effects on tilapia, and the vaccine significantly promoted fish growth and development when administered through Im + Or or Or immunization. Following vaccination, innate immunity parameters including SOD, ACP and CAT activities were all significantly enhanced. Additionally, specific serum IgM antibodies reached their highest level at the 6th week post vaccination. Skin and intestinal mucus IgT antibodies reached peaked at the 6th and 7th week post vaccination, respectively. The relative peak expression values for IL-8, IL-12, MHC-I, MHC-II, IgM, IgT, CD4, CD8, TNFα, IFNγ from Im + Ip group were significantly higher than those in Ip group, Im + Or group and Or group in most cases (p < 0.05). Importantly, the relative protection survival of Im + Ip group was the highest (78.6%), followed by the Ip group (71.4%), the Or group (64.3%) and the Im + Or group (57.1%). In summary, this study encourages further research on multi-channel immunization strategies of other kinds of vaccines in other aquatic economic animals to improve their disease resistance.

Dietary supplementation of Nile tilapia (Oreochromis niloticus) diets with bay laurel (Laurus nobilis): alleviation of oxidative stress and amelioration of immune response, serum biochemistry, and resistance against Aeromonas hydrophila

Herbal plants can enhance immunity and alleviate oxidative stress in fish. Therefore, the present work was performed to evaluate the effects of bay laurel (Laurus nobilis) on growth, immunity, antioxidant activities, disease resistance, and hematology in Nile tilapia (Oreochromis niloticus). A total of 225 Nile tilapia fingerlings (average weight 15.36 ± 0.04 g) were divided into five treatment groups and fed with bay laurel at 0, 10, 15, 20, and 25 g/kg diet for 90 days. A completely randomized design with three replications was applied. The significantly (p < 0.05) improved weight growth (WG), food conversion ratio (FCR), average daily growth (ADG), protein efficiency ratio (PER), and survival rate were observed in fish fed with bay laurel-supplemented diet at the rate of 15 g/kg. Significantly improved red blood cells (RBCs) count, white blood cells (WBCs), hemoglobin (Hb), and significantly declined alanine aminotransaminase (ALT) and aspartate transaminase (AST) were found in the same diet-fed group. The immune response parameters such as nitro blue tetrazolium (NBT), lysozyme activity, phagocytic activity, total serum protein, serum albumin, serum globulin, and albumin-globulin ratio were found significantly improved at 15 g/kg bay laurel supplemented diet. The improved antioxidant response (catalase, glutathione peroxidase, malondialdehyde, total antioxidant activity) was also observed in the same diet-fed group. Relative percent survival after the fish challenged against Aeromonas hydrophila was significantly (p < 0.05) different. Overall, bay laurel supplementation at a 15 g/kg diet improved the nutritional physiology and immunity and, therefore, could be a potential growth-promoting feed additive for aquaculture development.

Effect of seasonal variation and farming systems on the properties of Nile tilapia gelatin extracted from scales

Although fish gelatin has become a research hotspot in recent years, researchers and manufacturers are still looking for high-quality sources of fish galatin to meet the commercial demand for safer gelatin.became This study aimed to evaluate the impact of seasonal variation and farming systems on the properties of gelatin extracted from Nile tilapia scales. Gelatin extracted from farmed tilapia had lowest impurities, higher clarity as well as desirable color characteristics (L* = 65.95 and a* = -0.33). The protein and fat composition of Wild (91.00 ± 0.00c) and 1.94 ± 0.05a respectively were higher than farmed gelatin of protein (91.00 ± 0.00c) and fat (0.84 ± 0.08b) but gelatin from the farmed type were clearer (98.30 ± 0.28a) than wild type (94.60 ± 0.28b). In addition, the XRD analysis confirmed its amorphous structure (2θ = 11°, 21°. 29°, and 31°). The gelatin extracted from wild tilapia showed an average yield of 1.98 % and good physicochemical and functional properties. Furthermore, FTIR indicated a strong bond positioned in the amide I region (1650.88 cm-1) of the wild tilapia gelatin. Partial Least Square (PLS) confirmed that viscosity is positively correlated with melting temperature upon a unit change in gelatin yield. This work highlights the significance of farming systems and seasonal variation in extraction conditions and great parameter to comprehensively navigate the functional, biochemical, and physical properties of Nile tilapia gelatin for broadening both food and non-food industrial appliactions.

Formulation of an antiseptic topical cream based on chitosan extracted from the scales of the Nile tilapia (Oreochromis niloticus)

The Nile tilapia is a widely consumed fish, its scales dumped in nature as waste have been recovered in the formulation of antiseptic creams because of its high content in chitin, precursor of chitosan. Creams have the advantage of being more comfortable on the skin and allow prolonged administration of the active ingredient. Chitosan is obtained with a yield of 21.2%. FTIR analysis of chitosan showed numerous bands of phase groups present and a successful deacetylation assessed on the intensity of the bands at 1650 cm-1 and 1315 cm-1 and confirm by SEM analysis with an abundance of Carbone followed by EDS analysis. Solubilisation of chitosan in 2% acetic acid at 96% and the antibacterial activity test revealed antibacterial activity on Escherichia coli. The viscosity and the optimum spreading capacity of the cream base has been obtained at 14.65% for sesame oil, 9.08% for lanette and 1.26% for glycerine.

Single nucleotide polymorphisms in the MRFs gene family associated with growth in Nile tilapia

BACKGROUND

Muscle occupies most of the fish body, promoting the proliferation of fish muscle fibers can facilitate rapid growth and increase the body weight of fish. Some studiesSeveral previous suggest that Myogenic regulatory factors (MRFs) play an important role in the growth of fish.

OBJECTIVE

To investigate the association between the polymorphism of MRFs gene family and growth traits in Nile tilapia (Oreochromis niloticus), get more molecular markers for growth.

METHODS

Amplified the Nile tilapia MRFs family gene, including Myogenic determination 1 (Myod1), Myogenic determination 2 (Myod2), Myogenin (Myog), Myogenic factor 5 (Myf5), and Myogenic factor 6 (Myf6), single nucleotide polymorphism (SNP) were screened by Sanger sequencing.

RESULTS

A total of 16 SNP loci were screened, including six for Myf5, six for Myf6, one for Myog, one for Myod1 and two for Myod2. The growth traits were analyzed in relation to these 16 SNP loci, and the results indicated significant associations between all 16 SNP loci and the growth traits (P < 0.05). The linkage disequilibrium analysis revealed that D1 and D2 diplotypes of Myf5 gene, E1, E2, E3 and E4 of Myf6 gene, and F1 diplotype of Myod2 gene were significantly associated with superior growth traits.

CONCLUSION

There were 6, 6, 1, 1 and 2 growth-related molecular markers in Myf5, Myf6, Myog, Myod1 and Myod2 genes, respectively, which could be applied to the breeding of Nile tilapia.

Potential effects of probiotics (immunobacteryne; IMB) on growth performance, feed efficacy, blood biochemical, redox balance, nonspecific immunity and heat-shock protein expression of Nile tilapia (Oreochromis niloticus) fingerlings

The supplementation of aquafeed with probiotics is recommended for feasible aquaculture activities. Therefore, the aim of current study was to investigate the potential effects of probiotics on growth performance, feed utilization, biochemical attributes, redox status and immunity response as well as the transcription of heat-shock protein 70 (HSP70) and insulin-like growth factor-1 (IGF-1) genes of Nile tilapia (Oreochromis niloticus; n = 120). Fish with an initial weight of 8.17 ± 0.02 g/fish were randomly divided into four treatment groups and were fed diets containing 0, 0.5, 1 and 1.5 mg immunobacteryne (IMB)/kg diet respectively. Dietary IMB at 1.5 g/kg diet significantly improved the growth performance, feed consumption and growth hormone secretion of the experimental fish (p < 0.05). The 1 or 1.5 g IMB/kg diet boosted phagocytic activities and innate immune response. Serum total protein, total cholesterol, triglycerides and glucose were significantly increased in the groups that were fed 1 and 1.5 mg IMB/kg diet compared to the control (p < 0.05). Meanwhile, the levels of uric acid, creatinine, liver enzymes (aspartate transaminase and alanine transaminase) and cortisol hormone were significantly reduced in the aforementioned treated groups compared to the control (p < 0.05). All fish fed IMB-supplemented diet showed a significant increase in the expression of IGF-1 gene, while the transcription of HSP70 was significantly decreased (p < 0.05). In conclusion, the dietary inclusion of IMB (1 g/kg diet) enhanced growth promoters, feed efficacy, blood biochemical, redox balance and nonspecific immune responses in Nile tilapia fingerlings.

Effect of Substituting Soybean Meal in Oreochromis niloticus Diets with Pumpkin (Cucurbita maxima) Seed Cake on Water Quality, Growth, Antioxidant Capacity, Immunity, and Carcass Composition

A 10-week feeding experiment was performed to determine the impacts of partial substitution of soybean meal (SB) with pumpkin seed cake (PSC) in Oreochromis niloticus diets on water quality, growth rate, antioxidant capacity, immunity, and carcass composition. One hundred and fifty tilapia fish (average weight, 11.93 ± 0.17 g) were randomly allocated to five diets. The first diet (the basal diet) contained 420 g of SB per kg of feed. The remaining four diets, namely, D1, D2, D3, and D4, had SB partially replaced by PSC at 10%, 20%, 30%, and 40%, respectively. The results revealed that D4 and D1 significantly improved dissolved oxygen levels, while water temperature, pH, total ammonia, and nitrate levels were not significantly affected. Replacing SB with PSC significantly improved specific growth performance indicators and feed conversion compared to the control, with the D4 group showing the best values. Increasing PSC levels decreased serum glucose, aspartate aminotransferase, alanine aminotransferase, cholesterol, and triglyceride levels. In contrast, the D4 group had higher globulin, albumin, total protein, and lysozyme serum levels. Moreover, fish-fed PSC had significantly increased superoxide dismutase, glutathione peroxidase, and catalase activities and significantly decreased malondialdehyde levels. Increasing PSC substitution levels in fish diets increased the ash and crude lipid contents in the bodies of the fish, while crude protein and moisture decreased. In conclusion, replacing SB with PSC in fish diets significantly enhances growth performance, feed conversion, and fish health. Moreover, the findings suggest that PSC can be a promising alternative protein source for sustainable aquaculture practices.

Mitigating Aflatoxin B1-Induced Growth Impairment and Hepatic Stress in Nile Tilapia (Oreochromis niloticus): Comparative Efficacy of Saccharomyces cerevisiae and Silicate-Based Detoxifiers

The objective of this study was to detect the effects of acute aflatoxin B1 (AFB1) exposure in Nile tilapia (Oreochromis niloticus) and the effectiveness of Saccharomyces cerevisiae and silicate in reducing these effects. Two hundred and forty Nile tilapia fingerlings (16 ± 0.5 g) were randomly assigned to four experimental groups, each with 60 fish and three replicates. Control basal diet (Diet 1) and three test diets were formulated, where Diet 2 was supplemented with 200 ppb AFB1. Diets 3 and 4 were intoxicated with AFB1 (200 ppb) and supplemented with 0.5% S. cerevisiae or 0.5%, respectively. After 60 days, Diet 1 had considerably greater growth characteristics than the other groups (p < 0.05). Diet 2 revealed a reduced (p < 0.05) survival rate after 1 month of exposure. In addition, Diet 1 showed higher (p < 0.05) total protein and albumin levels than Diets 3 and 4. AFB1 residues were detected in the liver in fish-fed Diet 2, Diet 4, and Diet 3. Alanine aminotransferase, aspartate aminotransferase, creatinine, and urea levels increased (p < 0.05) in fish-fed Diet 2. The glutathione peroxidase, lysozyme, and catalase activity were decreased (p < 0.05) in the fish-fed Diet 2. The malondialdehyde level was significantly higher in fish given Diet 2 (p < 0.05) than in fish-fed Diets 3 and 4. Histopathological investigation of fish-fed Diet 2 revealed impaired liver and spleen; however, both treatments (Diets 3 and 4) successfully lowered inflammation and preserved liver and spleen integrities. In conclusion, AFB1 impaired growth performance and posed a severe health risk to Nile tilapia. Furthermore, S. cerevisiae alleviated the contamination of AFB1 effects more efficiently than silicate employed for toxin adsorption.

Nelumbo nucifera synthesized selenium nanoparticles modulate the immune-antioxidants, biochemical indices, and pro/anti-inflammatory cytokines pathways in Oreochromis niloticus infected with Aeromonas veronii

Bacterial infection is considered one of the major issues in fish culturing that results in economic losses. Metal nanoparticles are a cutting-edge and effective disease management and preventive strategy because of their antibacterial ability. In this investigation, the selenium nanoparticles were prepared by a biological method using Nelumbo nucifera leaves extract. The in-vitro antibacterial activity of N. nucifera synthesized selenium nanoparticles (NN-SeNPs) was tested against Aeromonas veronii. A treatment assay was conducted on 210 Oreochromis niloticus (average body weight: 27 ± 2.00 g). A preliminary approach was conducted on 90 fish for determination of the therapeutic concentration of NN-SeNPs which was found to be 4 mg/L. Fish (n = 120) were categorized into four groups for 10 days; G1 (control) and G2 (NN-SeNPs) were non-challenged and treated with 0 and 4 mg/L NN-SeNPs, respectively. While, G3 and G4 were infected with 2 × 106 CFU/mL of A. veronii and treated with 0 and 4 mg/L NN-SeNPs, respectively. NN-SeNPs exhibited an inhibition zone against A. veronii with a diameter of 16 ± 1.25 mm. The A. veronii infection increased the hepato-renal biomarkers (alanine and aspartate aminotransferases and creatinine) than the control group. An oxidative stress was the consequence of A. veronii infection (higher malondialdehyde and hydrogen peroxide levels with lower glutathione peroxidase superoxide, dismutase, and catalase activity). A. veronii infection resulted in lower immunological biomarker values (immunoglobulin M, lysozyme, and complement 3) with higher expression of the inflammatory cytokines (interleukin-1β and tumor necrosis factor-ɑ) as well as lower expression of the anti-inflammatory cytokines (interleukin-10 and transforming growth factor-β). Therapeutic application with 4 mg/L NN-SeNPs prevented the disease progression; and modulated the hepato-renal function disruptions, oxidant-immune dysfunction, as well as the pro/anti-inflammatory cytokines pathway in the A. veronii-infected fish. These findings suggest that NN-SeNPs, employed as a water therapy, can safeguard fish from the harmful effects of A. veronii and serve as a promising antibacterial agent for sustainable aquaculture.

Ameliorative effect of BIO-MOS® as a dietary supplementation on growth performance, physiological response, oxidative status, and immunity-linked gene expression in Nile tilapia (Oreochromis niloticus) fingerlings challenged with Aeromonas hydrophila

Background

Mannanoligosaccharides (MOS) usage in fish production has drawn more attention because of their positive benefits on disease resistance and fish performance.

Aim

The ongoing research was executed to assess the potential advantages of Bio-Mos® dietary supplementation regarding the growth outcomes, physiological response, oxidative biomarkers, and immunity-linked gene expression in Nile tilapia (Oreochromis niloticus) fingerlings exposed to bacterial infection with Aeromonas hydrophila.

Methods

Four experimental diets were developed using a 30% protein baseline diet, with Bio-Mos® added at variable levels; 0.0, 0.5, 1, and 2 g/kg, respectively. 240 healthy Nile tilapia fingerlings were split into 4 groups at random and assigned to 12 glass aquariums (three replicates of 20 fish/treatment). Diets were admitted at a 3% rate of fish biomass/aquarium for 8 weeks. Following the feeding trial, fish from every treatment were intraperitoneally injected with pathogenic A. hydrophila, and then observed for 15 days to record the survival rate percent (SR%) post challenge.

Results

Results revealed significant improvement in growth performance, physiological response, immunological parameters (phagocytic index, phagocytic activity, and lysozyme), and antioxidant parameters [catalase, malondialdehyde, glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD)] among Bio-Mos® treated groups. Moreover, Bio-Mos® increased the expression of tumor necrosis factor alpha and Interleukin 1β, genes linked to the liver immune system. Growth-related genes (GHr), antioxidant-related genes (SOD and GSH-Px). In fish subjected to pathogens, dietary MOS supplementation could significantly lower oxidative stress, showing promise as a preventative supplement for Nile tilapia in place of antibiotics. On the other hand, Bio-Mos® considerably improved each of the three intestinal morphological measures (villus width, villus length, and crypt depth), showing the best overall intestinal structure-improving impact. The challenge with A. hydrophila caused marked degenerative alterations in the intestine, hepatopancreas, spleen, and posterior kidney of Nile tilapia, in the control group. However, lesion severity was greatly decreased and showed marked amelioration with an increased concentration of Bio-Mos®. The A. hydrophila-challenged groups revealed a 100% SR% mainly among the Bio-Mos® supplemented groups.

Conclusion

It is recommended to enrich the Nile tilapia fingerlings diets with 2 g.kg-1 of MOS for better results on the growth rate, physiological response, immunological response, and intestinal absorptive capacity.

Chitosan nanogel aqueous treatment improved blood biochemicals, antioxidant capacity, immune response, immune-related gene expression and infection resistance of Nile tilapia

Candida albicans is a pathogenic yeast recently associated with diverse diseases in aquaculture. The present study investigated the efficacy of chitosan nanogel (CNG) in ameliorating effects of C. albicans on Nile tilapia (Oreochromis niloticus). Fish were randomly distributed into four groups (control, waterborne CNG at 75 μg/L, intraperitoneally challenged with C. albicans (1.8 × 107 CFU/mL), and waterborne CNG at 75 μg/L + C. albicans at 1.8 × 107 CFU/mL). Results showed that C. albicans infection reduced survival rate (57.5%) and caused marked clinical symptoms in fish among all infected groups. Substantial declines in immunological (complement 3, lysozyme, and immunoglobulin M), protein (total protein and non-albumin protein), and antioxidant (catalase, glutathione peroxidase, and superoxide dismutase) biochemical endpoints were exhibited, The C. albicans infected group also showed marked down-regulation in the expression of immune-related genes, including toll-like receptor 2 (TLR-2), transforming growth factor beta2, tumor necrosis factor alpha, interleukins (IL-1β, IL-6, and IL-10), and antiapoptotic gene (B-cell lymphoma, BCL-2). The expression of the apoptotic gene (Bcl-2 associated X protein, BAX) was up-regulated in fish challenged by C. albicans. The application of waterborne CNG to fish challenged with C. albicans infection improved fish survival (79.5%) and all other measured parameters. The main finding of this work was that CNG is a nanotechnology with potential for preventing degraded health status by C. albicans infection in tilapia, and thus has promise as an intervention in aquaculture settings.

Impact of Sel-Plex® dietary supplementation on growth performance, physiological response, oxidative status, and immunity-linked gene expression in Nile tilapia (Oreochromis niloticus) fingerlings challenged with Aeromonas hydrophila

Background

Organic selenium (Sel-Plex®) supplementation holds considerable promise for improving the effectiveness of fish production.

Aim

This experiment was accomplished to judge the potential benefits of Sel-Plex® nutritional additive on growth outcomes, physiological response, oxidative status, and immunity-linked gene expression in Nile tilapia (Oreochromis niloticus) fingerlings exposed to bacterial infection with Aeromonas hydrophila.

Methods

Utilizing a basal diet of 30% protein, four experimental diets were prepared, each of which contained Sel-Plex® at concentrations of 0.0, 0.5, 1, and 2 mg/kg, respectively. Three replicates of 20 fish/treatment were used using 240 healthy Nile tilapia fingerlings. Fish were placed in 12 glass aquariums and separated into 4 groups at random. For the entire span of 8 weeks, diets were admitted to fish at a 3% rate of fish biomass/aquarium. After the feeding trial, pathogenic A. hydrophila was intraperitoneally injected into fish of each treatment, and fish were observed for 15 days to track the survival rate (SR) after the challenge.

Results

Growth performance, physiological response, immunological parameters (phagocytic activity, phagocytic index, and lysozyme), and antioxidant parameters [catalase, superoxide dismutase (SOD), malondialdehyde, and glutathione peroxidase (GPx)] were noticeably improved in Sel-Plex® treated groups. Moreover, Sel-Plex® increased gene expression linked with the immune system in the liver (tumor necrosis factor-alpha and interleukin 1β), to growth (insulin-like growth factor 1 and growth hormone receptor), and antioxidants (SOD and GPx). Under pathogen-challenge conditions, the employed dietary Sel-Plex® supplementation could successfully lower fish oxidative stress, offering a potential preventive additive for Nile tilapia instead of antibiotics. On the other hand, Sel-Plex® significantly enhanced each of three intestinal morphological measurements (villus width, villus length, and crypt depth), demonstrating the greatest influence on the improvement of intestinal structure overall. In the Nile tilapia control group, the infection with A. hydrophila caused noticeable degenerative alterations in the gut, hepatopancreas, spleen, and posterior kidney. The severity of the lesion was significantly reduced and significantly improved with higher Sel-Plex® concentrations. Sel-Plex® supplemented groups had 100% SRs among the A. hydrophila-challenged groups.

Conclusion

It could be advised to enrich the diets of Nile tilapia fingerlings with 1-2 mg.kg-1 of Sel-Plex® to enhance growth rate, physiological response, immunological reaction, and intestinal absorptive capacity.

Summer mortality syndrome bacterial pathogens in farmed Nile tilapia (Oreochromis niloticus)

Background

The high summer mortality in many fish farms, which had detrimental economic and social implications, was a serious challenge that the fish industry had to deal with.

Aim

With an examination of the most effective antibiotic, the ongoing research was intended to shed light on the identification of the main bacterial pathogens associated with the summer mortality syndrome in the diseased farmed Nile tilapia.

Methods

Six hundred dead Nile tilapia samples that had suffered from summer mortality were collected from several fish farms between May and October of 2022. The gathered fish displayed hemorrhagic areas on the skin, scale detachment, fin degeneration, erosions, skin ulcers, and corneal opacity with unilateral and/or bilateral exophthalmia. The most prominent internal appearance was swelling of the internal organs with sanguineous ascetic fluid.

Results

There were 225 bacterial isolates found. Six species were identified through phenotypic and biochemical analysis; they were Aeromonas, Vibrio, Streptococcus, Pseudomonas, Enterococcus, and Edwardsiella spp., in descending percentage, respectively. Aeromonas spp., Vibrio spp., and Streptococcus spp. were the three most frequent isolated bacterial pathogens. The identification of Aeromonas hydrophila, Vibrio spp., and Streptococcus iniae, the three most common bacterial isolates, was confirmed by molecular analysis by polymerase chain reaction. Most of the tested strains were found to be responsive to Ciprofloxacin (CIP), Gentamicin (CN), and Chloramphenicol (C) but resistant to Amoxicillin (AMX), according to an antibiotic sensitivity test.

Conclusion

The three most dangerous common bacterial infections discovered during mass-farmed tilapia summer mortality are A. hydrophil a, Vibrio sp., and S. iniae. This makes it clear that high water temperatures may raise the possibility of bacterial infections, which could cause widespread tilapia mortality and substantial financial losses. Therefore, it is crucial to maintain a beneficial fish culture, environment, and husbandry practices to enhance the tilapia-rearing environment and lessen the virulence of the disease. Isolated bacterial strains showed low levels of resistance to AMX but were vulnerable to CIP, CN, and C.

C33 for Enhancing Nile Tilapia (Oreochromis niloticus) Cultures

The bacterium strain Cetobacterium sp. C33 was isolated from the intestinal microbial content of Nile tilapia (O. niloticus) under anaerobic conditions. Given that Cetobacterium species are recognized as primary constituents of the intestinal microbiota in cultured Nile tilapia by culture-independent techniques, the adaptability of the C33 strain to the host gastrointestinal conditions, its antibacterial activity against aquaculture bacterial and its antibiotic susceptibility were assessed. The genome of C33 was sequenced, assembled, annotated, and subjected to functional inference, particularly regarding pinpointed probiotic activities. Furthermore, phylogenomic comparative analyses were performed including closely reported strains/species relatives. Comparative genomics with closely related species disclosed that the isolate is not phylogenetically identical to other Cetobacterium species, displaying an approximately 5% sequence divergence from C. somerae and a 13% sequence divergence from Cetobacterium ceti. It can be distinguished from other species through physiological and biochemical criteria. Whole-genome annotation highlighted that Cetobacterium sp. nov. C33 possesses a set of genes that may contribute to antagonism against competing bacteria and has specific symbiotic adaptations in fish. Additional in vivo experiments should be carried out to verify favorable features, reinforcing its potential as a probiotic bacterium.

Evolutionarily conserved IL-27β enhances Th1 cells potential by triggering the JAK1/STAT1/T-bet axis in Nile tilapia

As a pleiotropic cytokine in the interleukin (IL)-12 family, IL-27β plays a significant role in regulating immune cell responses, eliminating invading pathogens, and maintaining immune homeostasis. Although non-mammalian IL-27β homologs have been identified, the mechanism of whether and how it is involved in adaptive immunity in early vertebrates remains unclear. In this study, we identified an evolutionarily conserved IL-27β (defined as OnIL-27β) from Nile tilapia (Oreochromis niloticus), and explored its conserved status through gene collinearity, gene structure, functional domain, tertiary structure, multiple sequence alignment, and phylogeny analysis. IL-27β was widely expressed in the immune-related tissues/organ of tilapia. The expression of OnIL-27β in spleen lymphocytes increased significantly at the adaptive immune phase after Edwardsiella piscicida infection. OnIL-27β can bind to precursor cells, T cells, and other lymphocytes to varying degrees. Additionally, IL-27β may be involved in lymphocyte-mediated immune responses through activation of Erk and JNK pathways. More importantly, we found that IL-27β enhanced the mRNA expression of the Th1 cell-associated cytokine IFN-γ and the transcription factor T-bet. This potential enhancement of the Th1 response may be attributed to the activation of the JAK1/STAT1/T-bet axis by IL-27β, as it induced increased transcript levels of JAK1, STAT1 but not TYK2 and STAT4. This study provides a new perspective for understanding the origin, evolution and function of the adaptive immune system in teleost.

Identification of key overlapping DEGs and molecular pathways under multiple stressors in the liver of Nile tilapia (Oreochromis niloticus)

The identification of key genes and molecular pathways that are involved in the response to stressors is crucial for controlling stress in fish and sustainable aquaculture. Environmental stressors can induce stress responses in aquatic animals, resulting in compromised immune function, inhibited growth, and increased mortality rates. mRNA-seq analysis provides a powerful tool to identify key genes and pathways associated with stress response. In the present study, mRNA-seq analysis was employed to identify key overlapping differentially expressed genes (DEGs) and molecular pathways under salinity, nitrite, copper, and pH stress in the liver of Nile tilapia (Oreochromis niloticus). The pathways associated with the immune response, oxygen transport, homeostasis, and oxidative stress were enriched across all stressors. The top KEGG pathways were complement and coagulation cascades, PPAR signaling pathway, and cardiac muscle contraction. The top GO enrichment terms were oxidoreductase activity, aerobic respiration, endopeptidase inhibitor activity, endopeptidase regulator activity, heme binding, and iron ion binding. The complement genes (C3, C4, C5, factor B, and factor H), alpha-2-macroglobulin (A2M), hemoglobin subunit epsilon (HBE), hemoglobin subunit alpha (HBA), coagulation factor genes (XI and X) and the cytochrome c oxidase (COX) gene family (cox1, cox2, cox3, cytochrome P450) were identified as key shared genes across multiple stressors. The discovery of these genes and molecular pathways provided a better understanding of the molecular mechanism underlying the stress response in Nile tilapia. The results of the present study can facilitate the development of stress management strategies in Nile tilapia.

isolated from farmed Nile tilapia (Oreochromis niloticus) in the Philippines

AIMS

Motile Aeromonas septicaemia (MAS) caused by motile Aeromonas species is an important disease in farmed freshwater fish due to intensification of culture and improper farm practices. This study characterized and profiled motile Aeromonas species recovered from clinically sick tilapia farmed in the Philippines, with a view to identifying targeted disease prevention and control measures against MAS in farmed tilapia species.

METHODS AND RESULTS

Sixteen isolates from diseased farmed Nile tilapia were identified as Aeromonas veronii (n = 14), Aeromonas caviae (n = 1), and Aeromonas dhakensis (n = 1). Five biochemical profiles using API 20E were exhibited by the A. veronii strains giving an unreliable identification. A high level of agreement was observed in identifying the Aeromonas strains using 16S rRNA and rpoD gene sequencing, although the latter has a higher discriminatory value. Three or more virulence genes dominated by cytotoxic enterotoxin act and aerolysin aer were detected. Different genotypes based on virulence gene clustering suggested varied mechanisms used by Aeromonas to colonize and infect or to mutualistically co-exist with the fish. Acquired multiple antibiotic resistance was found in a single A. veronii isolate. All were susceptible to enrofloxacin, oxolinic acid, florfenicol, and chloramphenicol. Tetracycline and sulfonamide resistances and class 1 integron were detected in three A. veronii isolates.

CONCLUSION

Several strains of motile aeromonads, especially A. veronii, which have varied genotypes based on virulence, biochemical profile, and antibiotic resistance, are involved in MAS in natural disease outbreaks in farmed Nile tilapia in the Philippines.

Effects of dietary supplementation of Bacillus subtilis DSM 32315 on growth, immune response and acute ammonia stress tolerance of Nile tilapia (Oreochromis niloticus) fed with high or low protein diets

Aquatic animals have benefited from Bacillus subtilis-based probiotics over the past few decades. This study evaluated the effects of B. subtilis DSM 32315 probiotics as a feed additive on growth, immune response and resistance to acute ammonia challenge in Nile tilapia. Specifically, four supplemental levels (0%, 0.1%, 0.2%, and 0.3%) of B. subtilis probiotics were tested under two dietary protein levels (32% and 28%). Five replicate tanks were randomly allotted to each dietary treatment, with each tank containing 30 Nile tilapia. After 8 weeks of feeding, Nile tilapia in each tank were exposed to 43.61 mg/L of total ammonia nitrogen for 48 h. The results revealed that reducing protein levels from 32% to 28% did not affect growth performance or antioxidant capacity. However, the low protein diet tended to induce an inflammatory effect shown by increased expressions of TGF-β and IFN-γ genes (P < 0.05) in the liver. The impact was alleviated by the probiotic supplementation. Compared with the non-supplemented group, 0.1% probiotic supplementation remarkably increased plasma lysozyme activity, total antioxidant capacity and complement C3 and interleukin-10 mRNA levels (P < 0.05) in the 28% protein diet, while higher supplementation of probiotics (0.3%) was shown to be beneficial for the high protein diet (32%). In both the dietary protein levels, 0.1% supplementation of probiotics promoted the antioxidant capacity of Nile tilapia before exposure to ammonia stress but higher probiotic supplementation (0.3%) proved to be necessary under ammonia stress as evidenced by higher fish survival rate. Results exhibited that supplementation with B. subtilis probiotics had a better effect on the intestinal morphology (villi height and width) regardless of protein levels. In conclusion, dietary supplementation of B. subtilis DSM 32315 probiotics at 0.1% in the low protein diet and up to 0.3% in the high protein diet showed beneficial effects on the growth, immunity, and antioxidant capacity of Nile tilapia. Under ammonia stress conditions, the higher supplementation of B. subtilis DSM 32315 probiotics at 0.3% improves stress tolerance of Nile tilapia despite the two dietary protein levels (32%; 28%).

Monoclonal antibody generated against Nile tilapia (Oreochromis niloticus) IgT heavy chain using a peptide-based strategy

Teleost IgT/Z plays a principal role in the defense mechanisms against infectious agents in the mucosal compartments and in systemic immunity. Previously, Nile tilapia (Oreochromis niloticus) IgT was discovered and characterized at transcription level. In this work, we generated a monoclonal antibody (mAb) that specifically recognized the Nile tilapia IgT. BALB/c mice were immunized with three synthetic peptides conjugated to KLH. The sequences of these peptides derived from the constant region of the Nile tilapia IgT heavy chain. ELISA and Western blotting confirmed the specificity of the polyclonal sera and the culture supernatant from a positive hybridoma clone. We observed immunoreactivity against a recombinant IgT fragment and native IgT in skin mucus. The anti-IgT mAb did not cross-react with purified tilapia IgM. Direct ELISA analysis allowed the quantification of skin mucus IgM and IgT concentrations. Flow cytometry analysis revealed differences in the percentage of IgT⁺ B cell populations between juveniles and adults in peripheral blood, head kidney and spleen lymphocytes and among the tissues analyzed. For further validation of the anti-IgT mAb utility, a recombinant vaccine candidate against sea lice (TT-P0 Ls) was injected into juvenile tilapia. Direct ELISA results revealed a differential secretion of skin mucus IgT and IgM after immunostimulation. In addition, the percentages of IgT⁺ B cells were determined at 7 days after booster and ex-vivo stimulation by flow cytometry. This mAb constitutes an important immunological tool to study the biological function and structural characteristics of tilapia IgT.

Potential role of dietary Boswellia serrata resin against mancozeb fungicide-induced immune-antioxidant suppression, histopathological alterations, and genotoxicity in Nile tilapia, Oreochromis niloticus

This study was established to look into the toxicological consequences of chronic exposure to a fungicide (mancozeb; MAZ) on the immune-antioxidant response, gene expressions, hepato-renal functions, and histological pictures of Nile tilapia (Oreochromis niloticus). Additionally, the effectiveness of Indian frankincense resin extract (IFRE) to mitigate their toxicity was taken into account. Fish (n =240; average body weight: 22.45 ± 2.21 g) were randomized into four groups for eight weeks in six replicates (control, IFRE, MAZ, and IFRE + MAZ), where ten fish were kept per replicate. The control and IFRE groups received basal diets that included 0.0 and 5 g/kg of IFRE without MAZ exposure. The MAZ and IFRE+MAZ groups received the same diets and were exposed to 1/10 of the 96-h of LC50 of MAZ (1.15 mg/L). The outcomes displayed that MAZ exposure resulted in a lower survival rate (56.67 %) and significantly decreased levels of immune-antioxidant variables (antiprotease, complement3, phagocytic activity, lysozyme, glutathione peroxidase, superoxide dismutase, and total antioxidant capacity) compared to the control group. The MAZ-exposed fish showed the greatest levels of lipid peroxide (malondialdehyde), alkaline phosphatase, alanine amino-transferase, and stress indicators (cortisol and glucose). Additionally, histopathological alterations, including vacuolation, severe necrosis, degeneration, and mononuclear cell infiltrations in the hepatic, renal, and splenic tissues resulted, besides a reduction in the melanomacrophage center in the spleen. A down-regulation of immune-antioxidant-associated genes [toll-like receptors (TLR-2 and TLR-7), nuclear factor kappa beta (NF-κβ), transforming growth factor-beta (TGF-β), phosphoinositide-3-kinase regulatory subunit 3 gamma b (pik3r3b), interleukins (IL-1β and IL-8), glutathione synthetase (GSS), glutathione peroxidase (GPx), and superoxide dismutase (SOD)] were the consequences of the MAZ exposure. Remarkably, the dietary inclusion of IFRE in MAZ-exposed fish augmented the immune-antioxidant parameters, including their associated genes, decreased stress response, and increased survival rate (85 %) compared with the MAZ-exposed fish. Moreover, dietary IFRE improved hepato-renal function indices by preserving the histological architecture of the hepatic, renal, and splenic tissues. The insights of this study advocate the use of an IFRE-dietary addition to protect Nile tilapia from MAZ toxicity, which provides perspectives for future implementations in enhancing fish health for sustainable aquaculture.

First Investigation of the Optimal Timing of Vaccination of Nile Tilapia (Oreochromis niloticus) Larvae against Streptococcus agalactiae

To investigate early immune responses and explore the optimal vaccination periods, Nile tilapia at 1, 7, 14, 21, 28, 35, and 42 days after yolk sac collapse (DAYC) were immersed in formalin-killed Streptococcus agalactiae vaccine (FKV-SA). A specific IgM was first detected via ELISA in the 21 DAYC larvae (0.108 g) at 336 h after vaccination (hav), whereas in the 28-42 DAYC larvae (0.330-0.580 g), the specific IgM could be initially detected at 24 hav. qRT-PCR analysis of the TCRβ, CD4, MHCIIα, IgHM, IgHT, and IgHD genes in 21-42 DAYC larvae immunized with the FKV-SA immersion route for 24, 168, and 336 hav revealed that the levels of most immune-related genes were significantly higher in the vaccinated larvae at all DAYCs than in the control larvae (p < 0.05) at 336 hav. Immunohistochemistry demonstrated stronger IgM signals in the gills, head kidney, and intestine tissues at 21, 28, and 35 DAYC in all vaccinated larvae compared with the control. Interestingly, at all DAYCs, FKV-SA larvae exhibited significantly higher survival rates and an increased relative percent survival (RPS) than the control after challenge with viable S. agalactiae, particularly in larvae that were immunized with FKV-SA at 168 and 336 hav (p < 0.05).

1758) in Victoria Nile as depicted from geometric morphometrics

BACKGROUND

Various anthropogenic activities continue to threaten the fish biodiversity of the East African water bodies such as the Victoria Nile. Although the Victoria Nile is a significant source of livelihood for human populations, the biology and ecology of Nile tilapia in this ecosystem remain understudied with little or no information on the morphology of the fish given varying and immense anthropogenic activities. Here, we use geometric morphometrics to examine the morphology/shape variations of Nile tilapia populations in Victoria Nile to gain insights into their current ecological state.

RESULTS

Our results indicate unexpectedly smaller Nile tilapia body weights in Victoria Nile than in L. Victoria. Despite this, nearly all the populations displayed a relative condition factor (Kn) of greater ≥1 suggesting a healthy stock. However, two populations, LMF and VN_Bukeeka demonstrated Kn values of less than one (< 1). We also report that some Upper and Lower Victoria Nile populations display morphological similarities. Apart from L. Albert, Nile tilapia populations from Lakes Victoria and Kyoga are morphologically divergent from the riverine ones. We note that Nile tilapia from Nalubale Dam Reservoir is morphologically distinct from the close neighbouring Victoria Nile populations which are likely allied to the influence of the Nalubale Hydroelectric power dam as a barrier.

CONCLUSION

Nile tilapia's morphological variation appears to be influenced by various anthropogenic disturbances notably, overfishing, hydroelectric power dams, and fish translocational history in Uganda. Management should enforce regulatory frameworks to avert human-mediated activities as these are likely to compromise the sustainability of the fisheries. Further studies are required to follow these populations with molecular genetics and environmental data to gain a deeper understanding of the fish species for informed sustainable management and conservation options.

Effect of aquaponic water and substratum material on biofilm formation by Aeromonas hydrophila

Aeromonas hydrophila is a zoonotic pathogen causing illness in fish and susceptible humans. This emerging pathogen has been isolated within aquaponic systems and could cause disease in fish and a hazard to humans consuming aquaponic produce. This study determined whether A. hydrophila from an aquaponic farm could form biofilms in aquaponic water and on materials used in these systems. A. hydrophila biofilm biomass and cell density in aquaponic water were evaluated by crystal violet staining and culture-based enumeration. Biofilm biomass and biofilm cell density were affected by the water source and A. hydrophila isolate (P < 0.05). A. hydrophila formed the most biomass from the beginning of deep-water culture (BDWC) water (OD570 0.202 ± 0.066) and the least from the end of deep-water culture (EDWC) water (OD570 0.140 ± 0.036; P < 0.05). Enumerated A. hydrophila from the biofilm varied among water sources; the fish tank water supported the greatest cell density (7.04 ± 0.71 log CFU/mL) while the EDWC supported the lowest cell density (6.76 ± 0.83 log CFU/mL). Biofilm formation was also evaluated on aquaponic materials such as nylon, polyvinyl chloride, polyethylene liner, bead filter, and foam. Biofilm formation on the liner had the greatest population (2.39 ± 0.022 log CFU/cm2), and the bead had the least (0.64 ± 0.039 log CFU/cm2; P < 0.05). Pathogenic organisms, such as A. hydrophila, may pose a greater risk to produce harvested from the BDWC and MDWC due to greater biofilm formation.

Prophylactic effects of dietary caper (Capparis spinosa) extracts on the control of Streptococcus agalactiae infection, growth, immune-antioxidant, and inflammation cytokine responses of Nile tilapia fingerlings

The antibacterial activity of aqueous (AE) or ethanolic extracts (EE) of caper (Capparis spinosa) against Streptococcus agalactiae was evaluated in vitro. Both caper extracts showed antagonistic activity against S. agalactiae and the inhibition zones in case of ethanolic extracts were larger than those of aqueous ones. Additionally, TEM investigations show that S. agalactiae cells treated with both C. spinosa extracts were damaged and degraded and this damage was greater in case of ethanolic extract. Another study was done to assess the promotion effects of dietary caper (C. spinosa) extracts on growth, antioxidant and immune activity, and inflammation cytokine responses of Nile tilapia (Oreochromis niloticus) and its resistance to S. agalactiae infection. However, fish (40 ± 2 g) were fed on diets containing 1.0 and 2.0 g/kg feed of each caper extract as well as the control group (free of caper) for 6 weeks. Fish were intraperitoneally injected (IP) with Streptococcus agalactiae at the end of the feeding trial, and fish mortality was tracked for additional ten days. Compared with other treatments, fish fed on 2.0 g EE/kg feed had higher counts of white and red blood cells as well as higher hemoglobin levels accompanied with lower AST and ALT activities. Antioxidant (superoxide dismutase and catalase activities) and immune, total protein, globulin, lysozyme, and immunoglobulin M) indices were increased along with significant decline in MDA levels in both caper extracts treated fish groups compared to the control group. Significant promotion in fish growth was affected positively with the increase in both caper extracts; particularly, the larger fish growth was observed in the treatment of 2.0 g EE/kg feed. Expressions of IL-1β and IL-8 were declined; meanwhile levels of IL-10, SOD and CAT genes were upregulated in fish fed on 2.0 g EE/kg feed compared to other groups. After being challenged with S. agalactiae infection, fish survival was considerably (P < 0.05) greater in fish groups that fed on diets with caper extracts; particularly 2.0 g EE/kg feed (75%); while all fish fed on the control one were dead. According to these findings, the antioxidant and immune response of Nile tilapia fingerlings is stimulated by ethanolic extract of caper (2.0 g/kg feed), which also enhanced the growth performance and fish resistance to S. agalactiae infection.

Stress-associated β -glucan administration stimulates the TLR - MYD88 - NFKB1 signaling pathway in Nile tilapia (Oreochromis niloticus)

There is evidence that the administration of β-glucan can effectively activate several defense mechanisms, such as the Tlr-Myd88-Nfkb1 pathway that induces the expression of immune cytokines. Thus, the objective of this work was to evaluate whether β-glucan acts on the mechanisms of gene transcription via the Tlr-Myd88-Nfkb1 pathway in Nile tilapia under stress after challenge with Streptococcus agalactiae. Therefore, we evaluated the expression of immune system genes such as toll-like receptors 1 (tlr1), toll-like receptors 2 (tlr2), primary myeloid differentiation response gene (myd88) and nuclear factor kappa B1 (nfkb1). A total of 408 fish were distributed in 24 polyethylene boxes and randomly divided into eight groups with 3 replications each: C15: Tilapias received a control diet (free of β-glucan) for 15 days and were sampled after the 15th day of the experiment; C15D: Tilapias received a control diet (free of β-glucan) for 15 days, were challenged on the 14th day and were sampled at the 15th day of the experiment; β15: Tilapias received experimental diet (1g kg-1 of β-glucan) for 15 days and were sampled after 15 days; β15D: Tilapias received an experimental diet (1g kg-1 of β-glucan) for 15 days, were challenged on the 14th day and were sampled at the 15th day of the experiment; C30: Tilapias received a control diet (free of β-glucan) for 30 days and were sampled on the 30th day of the experiment; C30D: Tilapias received a control diet (free of β-glucan) for 30 days, were challenged on the 29th day and were sampled at the 30th day of the experiment; β30: Tilapias received experimental diet (1g kg-1 of β-glucan) for 30 days and were sampled after 30 days and β30D: Tilapias received experimental diet (1g kg-1 of β-glucan) for 30 days, were challenged on the 29th day and were sampled at 30 of the experiment. In the fish sampled at 15 and 30 days of the experiment, after being anesthetized and killed by brain section, cranial kidney and spleen were collected for gene expression analysis. The analyzes showed that the association of β-glucan and stressful management modulated the immune system, using the Tlr-Myd88-Nfkb1 signaling pathway, indicating that this compound can be used to promote early defense and protect fish against diseases.

Sharing is caring? Barcoding suggests co-introduction of dactylogyrid monogeneans with Nile tilapia and transfer towards native tilapias in sub-Saharan Africa

Invasive Nile tilapias negatively impact native tilapia species through hybridisation and competition. However, the co-introduction of parasites with Nile tilapia, and subsequent changes in parasite communities, are scarcely documented. Monogeneans are known pathogens of cultured Nile tilapia, although little is known about their fate once Nile tilapias establish in new ecosystems. We investigate the parasitological consequences of Nile tilapia introduction on native tilapias in basins in Cameroon, the Democratic Republic of the Congo (DRC), and Zimbabwe, focusing on ectoparasitic dactylogyrids (Monogenea). Using the mitochondrial cytochrome oxidase c subunit I (COI) and nuclear 18S-internal transcribed spacer 1 (18S-ITS1) rDNA region of 128 and 166 worms, respectively, we evaluated transmission of several dactylogyrid species. Parasite spillover from Nile tilapia was detected for Cichlidogyrus tilapiae to Coptodon guineensis in Cameroon, Cichlidogyrus thurstonae to Oreochromis macrochir in the DRC, and Cichlidogyrus halli and C. tilapiae to Coptodon rendalli in Zimbabwe. Parasite spillback to Nile tilapia was detected for Cichlidogyrus papernastrema and Scutogyrus gravivaginus from Tilapia sparrmanii and Cichlidogyrus dossoui from C. rendalli or T. sparrmanii in the DRC, and Cichlidogyrus chloeae from Oreochromis cf. mortimeri and S. gravivaginus from O. macrochir in Zimbabwe. 'Hidden' transmissions (i.e. transmission of certain parasite lineages of species that are naturally present on both alien and native hosts) were detected for C. tilapiae and Scutogyrus longicornis between Nile tilapia and Oreochromis aureus and C. tilapiae between Nile tilapia and Oreochromis mweruensis in the DRC, and Cichlidogyrus sclerosus and C. tilapiae between Nile tilapia and O. cf. mortimeri in Zimbabwe. A high density of Nile tilapia occurring together with native tilapias, and the broad host range and/or environmental tolerance of the transmitted parasites, are proposed as factors behind parasite transmission through ecological fitting. However, continuous monitoring and the inclusion of environmental variables are necessary to understand the long-term consequences of these transmissions on native tilapias and to elucidate other underlying factors influencing these transmissions.