Eutrophication, Ammonia Intoxication, and Infectious Diseases: Interdisciplinary Factors of Mass Mortalities in Cultured Nile Tilapia

Impact of transport conditions and underlying disease on post-stocking survival of juvenile Lates calcarifer

Diseases caused by pathogens commonly occurring in the aquatic environment or those that are non-host specific are prevalent and threaten the rapid growth of tropical aquaculture. This study investigates causes of mortality in 12 batches of newly stocked juvenile Lates calcarifer from three different hatcheries. Cytology based on Diff-Quik™-stained tissue and blood smears provides rapid diagnosis of possible causes of mortality, while histopathology and haematology provide a better understanding of how prolonged transport and fish with existing chronic disease are more likely to experience elevated mortality post-stocking. Our findings showed that accumulation of ammonia during prolonged transport causes extensive damage to epithelial barriers in gastrointestinal tracts and depressed immunity due to marked hypoglycaemia, predisposing fish to acute Streptococcosis. Lates calcarifer with chronic bacterial enteritis developed severe hypoglycaemia, had low circulating total plasma protein, and suffered high mortality within 24 hours post-stocking. Hypoglycaemia and low circulating blood proteins disrupt osmoregulation and exacerbate dehydration, which is fatal in fish in sea water. Dying L. calcarifer tested PCR positive for scale drop disease virus (SDDV) at 28 days post-stocking showed a 10-fold elevation of white blood cell counts, severe vasculitis, and obstruction of blood supply to major organs. Destruction of important immune organs such as spleen is a hallmark of SDDV infection that explains high incidences of opportunistic Vibrio harveyi infections in 61% of fish with SDDV. Overall, this study reiterates the importance of stocking disease-free fish and reducing transport stress.

Implications of ammonia stress for the pathogenicity of Shewanella spp. in Oreochromis niloticus: effects on hematological, biochemical, immunological, and histopathological parameters

Environmental stressors (such as ammonia) in aquaculture could increase the risk of pathogenicity, posing a more severe threat to farmed fish. The aim of this study was to investigate the effects of ammonia stress on the pathogenicity of Shewanella spp. in Oreochromis niloticus. First, a 96-hour static test was used to determine the median lethal concentration (LC50) of unionized ammonia to Nile tilapia. After 96 h of exposure, the Un-ionized ammonia (UIA) LC50 was estimated to be 4.26 mg/L. Second, an experiment was conducted to test the effect of unionized ammonia stress on the pathogenicity of Shewanella spp. in O. niloticus for 30 days. A study involved 180 fish divided into six groups, with the first group serving as a control. The second group (AMN1/10) and the third group (AMN1/20) were not challenged and were exposed to 1/10 (0.42 mg/L) and 1/20 (0.21 mg/L) of the 96-hour LC50 of UIA, respectively. Then 0.2 mL (0.14 × 105) of Shewanella spp. was intraperitoneally injected into the fourth (SH), fifth (SH + AMN1/10), and sixth (SH + AMN1/20) groups, which were subjected to 0, 1/10 (0.42 mg/L), and 1/20 (0.21 mg/L) of the 96-hour LC50 of UIA, respectively. The survival rate, hematological indices, immunological parameters, and antioxidant activity of the fish significantly decreased when they were exposed to ammonia and Shewanella infection separately or together. Histopathological changes were also observed in the kidney and liver. Furthermore, both individual and combined exposures significantly altered renal and hepatic function, with notable increases in glucose and cortisol levels, as well as in the expression of proinflammatory cytokine genes (TNF-α and IL-1ß). However, the detrimental effects of co-exposure to ammonia stress and Shewanella infection were greater than those of separate exposures. As a result, we may say that increased ammonia concentrations enhance the infection of Shewanella spp. These findings could contribute to a better understanding of Shewanella infection in Nile tilapia.

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.

Nano-selenium impacts on growth performance, digestive enzymes, antioxidant, immune resistance and histopathological scores of Nile tilapia, Oreochromis niloticus against Aspergillus flavus infection

The present study examined the impacts of varying amounts of selenium nanoparticles (Se-NPs) as a natural antioxidant and metabolic regulator on growth performance, antioxidant capacity, digestive enzymes and immune resistance of Oreochromis niloticus challenged to Aspergillus flavus infection. For 60 days, fish were fed the experimental diet of 30% crude protein up to apparent satiation three times a day. Se-NPs were added to the control diet at different levels of 0.0 (control), 0.5 (T1), 1.0 (T2) and 1.5 (T3) mg/kg diet to fed monosex Nile tilapia fingerlings with average initial weight (4.5 ± 0.5 g). Fish were randomly distributed in 12 tanks 100 L at a density of 20 fish per tank after 2-week acclimation to represent four treatments in triplicates. The results indicated that the growth indices, feed efficiency and survival rate were significantly enhanced (P < 0.05) by incorporating Se-NPs up to 1 mg/kg diet. Furthermore, the haemato-biochemical parameters, digestive enzymes activity and antioxidant capacity of the fish were significantly improved (P < 0.05) at T2. When the fish were challenged with Aspergillus flavus, a decreasing mortality rate was observed, which clearly shows that selenium nanoparticles boosted the fish’s immune response at T2. The intestinal morphology as villus length, villus width, muscular fibres layer thickness and absorption intestinal zone after challenged with A. flavus infection were considerably enhanced (P < 0.05) by incorporating all Se-NP levels. Histopathological score significantly improved (P < 0.05) for the hepatopancreatic, intestinal, gills and muscle tissues at T2. The present study concludes that selenium nanoparticles up to 1.0 mg/kg diet can be efficiently used in tilapia feed to help boost fish production, immune system response and histopathological parameters.

Ammonia Toxicity in the Bighead Carp (Aristichthys nobilis): Hematology, Antioxidation, Immunity, Inflammation and Stress

Ammonia is one of the main environmental pollutants that affect the survival and growth of fish. The toxic effects on blood biochemistry, oxidative stress, immunity, and stress response of bighead carp (Aristichthys nobilis) under ammonia exposure were studied. Bighead carp were exposed to total ammonia nitrogen (TAN) concentrations of 0 mg/L, 3.955 mg/L, 7.91 mg/L, 11.865 mg/L, and 15.82 mg/L for 96 h. The results showed that ammonia exposure significantly reduced hemoglobin, hematocrit, red blood cell, white blood cell count, and platelet count and significantly increased the plasma calcium level of carp. Serum total protein, albumin, glucose, aspartate aminotransferase, and alanine aminotransferase changed significantly after ammonia exposure. Ammonia exposure can induce intracellular reactive oxygen species (ROS), and the gene expression of antioxidant enzymes (Mn-SOD, CAT, and GPx) increases at the initial stage of ammonia exposure, while MDA accumulates and antioxidant enzyme activity decreases after ammonia stress. Ammonia poisoning changes the gene expression of inflammatory cytokines; promotes the gene expression of inflammatory cytokines TNF-α, IL-6, IL-12, and IL-1β; and inhibits IL-10. Furthermore, ammonia exposure led to increases in stress indexes such as cortisol, blood glucose, adrenaline, and T3, and increases in heat shock protein 70 and heat shock protein 90 content and gene expression. Ammonia exposure caused oxidative stress, immunosuppression, inflammation, and a stress reaction in bighead carp.

A systematic review and meta-analysis of the relationship between farm management, water quality and pathogen outbreaks in tilapia culture

A systematic review and meta-analysis of on farm management and water quality as risk factors triggering pathogen outbreaks in tilapia culture is presented. A total of 121 papers from 28 countries, 37 devoted to management and 84 to water quality associated with the presence of pathogens in tilapia culture were analysed. Most of research has been made on ponds, focusing on bacteria and metazoans. Meta-analysis reveals the proportion of research showing statistical inferences between management (34%), water quality (38% for bacteria and 16.2% for metazoans) and pathogen outbreaks. The most cited parameters related to pathogens outbreaks were temperature (>30°C), dissolved oxygen (<5.0 mg/L), pH (<8.0) and ammonia (1.0 >mg/L) 65, 38, 32 and 34 papers, respectively. However, statistical inference was <20%. Meta-analysis reveals tendencies between high temperatures (30-35°C), low dissolved oxygen (<5 mg/L) and high NH₃ (1-5 mg/L) with pathogen outbreaks. Despite the knowledge about the relationship between management and water quality as factors for pathogen effects, most information is descriptive and empirical. Future research on tilapia culture outbreaks should be focused on the effects of multiple stressors affecting tilapia pathogen outbreaks, thereby generating strategies to prevent diseases and financial losses.

Utilising problematic waste to detect toxic gas release in the environment: fabricating a NiO doped CuO nanoflake based ammonia sensor from e-waste

Using problematic electronic waste to synthesise high-purity nanomaterials can enable sustainable production and create opportunities to divert waste from landfills. Reported here is a simple strategy for the controllable synthesis of in situ NiO doped CuO nanoflakes from waste flexible printed circuit boards (FPCBs) using a chemothermal microrecycling process, and the nanomaterial is then utilised for an ammonia (NH₃) sensor at room temperature. Characterisation of the nanoflakes confirmed the purity of the CuO phase with a monoclinic structure without the formation of the Cu₂O phase. The NiO doped CuO 2D nanoflakes made of an assembly of 1D nanorods with a high surface area of 115.703 m² g^-1 are selectively synthesised from the waste FPCBs and have outstanding gas sensing characteristics such as a high response, a fast response (11.7 s) and a recovery time of (21.5 s), good stability, and superior selectivity towards 200 ppm of NH₃ gas at room temperature (RT, 20 °C). From a broader perspective, the process opens up exciting new avenues explore the production of toxic gas sensing functional materials from toxic and problematic waste.

Clinico-pathological findings and expression of inflammatory cytokines, apoptosis, and oxidative stress-related genes draw mechanistic insights in Nile tilapia reared under ammonia-N exposure and Aeromonas hydrophila challenge

Fish diseases have a "stress-related" nature, whereas fish exposure to stressors will increase their susceptibility to infections. It was also noted that fish exposure to biotic and abiotic stressors would exaggerate the disease signs, elicit high mortalities, and cause severe economic losses. Motile aeromonad septicemia (MAS) is a major bacterial disease affecting a variety of finfish species throughout the globe and is caused by Aeromonas hydrophila. Herein, we have evaluated the impacts of ammonia-N stress and/or Nile tilapia challenge with pathogenic A. hydrophila on the clinical picture of MAS disease. Clinical signs, postmortem lesions, histoarchitectural changes, and gene transcription analysis were studied. Fish experimentally infected with A. hydrophila were exophthalmic and showed darkened skin. Moreover, opercular hyperemia, petechial hemorrhages, and gill congestion alongside dermal ulcerations were noticed in ammonia-exposed fish. On the other side, fish exposed to both stressors exhibited exophthalmia, corneal opacity, severe dropsy, and hemorrhagic dermal ulcerations. At the tissue levels, the histopathological lesions were exaggerated in the fish group exposed to ammonia stress and challenged with A. hydrophila than fish group exposed to each one alone. At the molecular levels, the mRNA expression analysis reveals significant upregulation of inflammatory cytokines such as interleukin-1 beta, CXC chemokine, and tumor necrosis factor-alpha in the kidney tissues of Nile tilapia exposed to ammonia and/or challenged with A. hydrophila. In a similar trend, the mRNA expression values of heat shock protein 70 (HSP70), oxidative stress related genes (SOD and CAT) and apoptosis-related genes (caspase 3, BAX, and cytochrome P450) were also increased in the hepatic tissues of fish exposed to singular or dual stressors. Interestingly, the highest expression levels of the above-mentioned genes were found in the fish group exposed to both stressors. Taken together, these findings indicate the occurrence of severe inflammatory and apoptotic changes in fish exposed to ammonia and infected with A. hydrophila more than each one alone. In contrast, there was a significant decrease in the expression values of the antioxidant enzyme glutathione-S-transferase (GST) in stressed fish, suggesting the occurrence of oxidative stress. This study will be helpful to draw mechanistic insights into the exposure of fish to ammonia stress and infection with A. hydrophila.

Downregulated pol-miR-140-3p induces the expression of the kinesin family member 5A against Streptococcus parauberis infection in olive flounder

MicroRNAs (miRNAs) are small non-coding RNAs that participate in various biological and cellular processes by regulating target gene expression. miRNAs are also known to play vital roles in the pathogenesis of various diseases, including infections, as well as the disease progression and defense responses. In this study, we examined the expression levels of pol-miR-140-3p and its target gene, kinesin family member 5A (KIF5A), in association with the Streptococcus parauberis (S. parauberis) infection, a major bacterial pathogen that causes streptococcosis in olive flounder (Paralichthys olivaceus). KIF5A is a heavy chain isoform of kinesin-1, which is known to be brain-specific, and this study is the first examination of KIF5A expression related to the regulation of miRNA in olive flounder (named PoKIF5A). There were significant differences in expression levels between infected and healthy olive flounder as the expression of pol-miR-140-3p in the infected fish was lower than that in the control, while the expression of PoKIF5A was higher in the infected fish than in the healthy controls. These contradictory results suggest that downregulated pol-miR-140-3p induces the expression of PoKIF5A against S. parauberis infection in olive flounder.

Application of Mussell-derived biosorbent to remove NH4+ from aqueous solution: Equilibrium and Kinetics

Mussel shells are often considered an abundant waste with no use. This study shows that the employment of mussel shells as a biosorbent for ammonium from water environment is completely possible. By using batch experimental method, optimal conditions for the ammonium adsorption onto mussel shells were determined. Specifically, those include a pH level of 8, contact time of 90 min, an initial ammonium concentration of 40 mg/l and the adsorbent dose of 700 mg/25 ml. With such operating conditions, experiments in laboratory aqueous solutions resulted in a maximum adsorption capacity of 2.33 mg/g, corresponded by 46.575% of efficiency. Adsorption isotherms and kinetics were well described with the Freundlich isothermal model, suggesting a heterogeneous adsorption process occurring on multilayers and both the pseudo-first-order and the pseudo-second-order, implying that the operational fundament was based on chemisorption. Analyses regarding SEM, EDS and FTIR were also implemented to identify the morphology, composition and functional groups of the adsorbent.

Fuzzy Optimization for the Remediation of Ammonia: A Case Study Based on Electrochemical Oxidation

This case study covers the application of the fuzzy optimization in simultaneously satisfying various constraints that include the compliance of ammonia and nitrate concentrations with stringent environmental standards. Essential components in the multi-criteria decision-making analysis is in the utilization of the Box-Behnken design (BBD) response equations, cost equations and the cumulative uncertainty of response towards the sodium chloride dosage, current density and electrolysis time parameters. The energy consumption in the electrochemical oxidation of ammonia plays an essential role in influencing the total operating cost analysis. The determination of boundary limits based on the global optimum resulted in the complete ammonia removal and USD 64.0 operating cost as its maximum boundary limits and the 40.6% ammonia removal and USD 17.1 as its minimum boundary limits. Based on the fuzzy optimal results, the overall satisfaction level incurred a decrease in adhering with a lower ammonia standard concentration (10 mg/L at 80.3% vs. 1.9 mg/L at 76.1%) due to a higher energy consumption requirement. Global optimal fuzzy results showed to be highly cost efficient (232.5% lower) as compared to using BBD alone. This demonstrates the practicality of fuzzy optimization applications in the electrochemical reactions.

Mass mortality of fish and water quality assessment in the tropical Adyar estuary, South India

Mass mortality of fishes was reported at the Adyar estuary, South India, during November 2017. The probable reasons for fish mortality are analyzed in this paper. Critical assessments on water quality parameters including the metal concentrations, nutrients, and histology of gills and liver of fish (Mugil cephalus) isolated from the impact zone were performed. Among the metals observed, chromium showed levels (3.64 ± 0.001 mg L^-1) much above the average permissible limits (0.1 mg L^-1). The measured values of physico-chemical parameters in the impact zone are as follows: dissolved oxygen 4.7 ± 0.22 mg L^-1, total alkalinity 132 ± 4 CaCO₃ mg L^-1, salinity 5.3 ± 0.3 PSU, temperature 27.8 ± 0.16 °C, nitrate, 1.66 ± 0.48 mg L^-1, nitrite 0.01 ± 0.0008 mg L^-1, ammonia 0.03 ± 0.001 mg L^-1, phosphate 1.52 ± 0.002 mg L^-1, and silicate 13.85 ± 3.1 mg L^-1. The low salinity could have escalated the toxicity of the metal. In addition, histology of gills and liver showed cellular necrosis, epithelial lifting, hyperplasia, edema, mucous cell proliferation in the gills, cytoplasmic vacuolation of hepatocytes, and degeneration of liver which reveal that chromium toxicity is the most probable cause for mass mortality.

Histopathological, biochemical and molecular studies on the toxic effect of used engine oil on the health status of Oreochromis niloticus

The accidental spilling of petroleum oils into natural water resources expose fishes in the effluent area to serious problems.. Oreochromis niloticus were used in the current study as a model to investigate the toxicity of used engine oil and to evaluate the protective role of vitamin C against this toxicity. The oil concentration used in this study was previously determined to be 0.25 ml/l by 96 h-LC50. After 21 days of engine oil exposure, haematological and biochemical analyses revealed significant reduction in RBCs counts, haemoglobin concentrations and total proteins. However, ALT, AST and glucose levels were significantly increased by the end of the experiment indicating the damaging effects of the oil on fish tissues. Oxidative stress biomarkers were also measured; liver CAT activity was significantly decreased in the oil exposed group compared to control group, while MDA levels were significantly elevated. Histopathological examination showed the presence of several alterations in hepatic and branchial tissues in exposed group compared to the control group. Significant elevations in CYP1 A1 mRNA expression levels in hepatic tissue were also detected in the group exposed to used engine oil compared to the control group. However, supplementation of fishexposed to used engine oil with vitamin Csignificantly enhance the biochemical, oxidative and histological parameters.

Dietary administration of probiotics modulates non-specific immunity and gut microbiota of Nile tilapia (Oreochromis niloticus) cultured in low input ponds

Poor culture conditions in low input ponds make fish highly susceptible to infectious pathogens which lead to diseases and mortalities yet the effects of probiotics on immunity, gut microbiota and microbiological quality of fish in low input ponds are unknown. Nile tilapia, Oreochromis niloticus fingerlings (40 g) were randomly stocked at 50 fish m⁻³ in 1.25 m³ cages in low input ponds. The fish were fed on diets supplemented with either Saccharomyces cerevisiae (1 × 10¹⁰ CFU g⁻¹) or Bacillus subtilis (1 × 10⁹ CFU g⁻¹) at six levels: Diet 0 (No probiotic); S. cerevisiae at 2 g kg⁻¹ (Diet 1); 4 g kg⁻¹ (Diet 2) and 6 g kg⁻¹ (Diet 3) and B. subtilis at 5 g kg⁻¹ (Diet 4); 10 g kg⁻¹ (Diet 5) and 15 g kg⁻¹ (Diet 6) for 180 days. Results indicate that hemato-immunological parameters (hemoglobin (Hb), red blood cells (RBC), white blood cells (WBC) serum protein, albumin, globulin and lysozyme activity) were significantly higher in fish fed on probiotic treated diets compared to the control (P < 0.05). On the contrary, fish fed on Diet 6 presented significantly similar Hb and globulin values compared to the control (P > 0.05). Additionally, fish fed on probiotic treated diets retained the probiotics in their guts and lower microbial load was realized in their muscle (P < 0.05). In conclusion, B. subtilis and S. cerevisiae supplementation in diets of Nile tilapia reared in low input ponds improves immunity, manipulates gut microbiota and enhances fish flesh quality.

Efficacy of Injectable and Immersion Polyvalent Vaccine against Streptococcal Infections in Broodstock and Offspring of Nile tilapia (Oreochromis niloticus)

A vaccine against streptococcosis, lactococcosis and enterococcosis in tilapia was formulated, ME-VAC Aqua Strept, as a polyvalent inactivated vaccine containing Streptococcus agalactiae, S. iniae, Lactococcus garvieae and Enterococcus faecalis along with a nano-particulate adjuvant. Use of ME-VAC Aqua Strept by injection or immersion resulted in an improved non-specific and adaptive immunity of broodstock and offspring. Intra-peritoneal vaccination of tilapia broodstock increased the total leukocyte count, phagocytosis, lysozyme activity, antibody titer, number of seeds/vaccinated broodstock, seeds quality and survival rates. Also, immersion mass vaccination of tilapia larvae provided a long period of protection up to three months, with a relative percent of survivability (RPS) not less than 60% at this time. To our knowledge, this vaccine may be the first to offer a combined protection against streptococcosis, lactococcosis and enterococcosis in tilapia. The results support the use of this vaccine as an effective tool for disease control and well-being of fish.