Dietary galactooligosaccharide elicits positive effects on non-specific immune parameters and growth performance in Caspian white fish (Rutilus frisii kutum) fry

Rosmarinic acid alone or in combination with Lactobacillus rhamnosus ameliorated ammonia stress in the rainbow trout, Oncorhynchus mykiss: growth, immunity, antioxidant defense and liver functions

Rosmarinic acid (RS) and Lactobacillus rhamnosus (LR) were added singularly or in combination to rainbow trout (Oncorhynchus mykiss) diets to test their efficacy in the protection against ammonia stress. Fish (31.4±0.6 g) were randomly allocated to six groups in three replicates, as follows: T1: basic food as control, T2: LR with a concentration of 1.5 × 108 CFU/g, T3: LR with a concentration of 3 × 108 CFU/g, T4: 1 g RS/kg, T5: 3 g RS/kg, and T6: 1.5 × 108 CFU/g LR + 1 g RS/kg and T7: 3 × 108 CFU/g LR + 3 g RS/kg. After 60 days feeding, fish exposed to 0ammonia stress. After the feeding period, the supplemented fish had the highest final body weight (FW), weight gain (WG), and specific growth rate (SGR), and the lowest feed conversion ratio (FCR) as compared with the control group (P<0.05). Amylase, protease and lipase activities were noticed markedly higher in fish supplemented with 1.5 × 108 CFU/g LR + 1 g RS/kg and 1.5 × 108 CFU/g LR diets compared to the control (P<0.05). Generally, fish in supplemented diets, particularly T2 and T6 groups, had the highest lysozyme, alternative complement activity (ACH50), total Ig, nitroblue tetrazolium test (NBT), myeloperoxidase (MPO), complement component 3 (C3), complement component 4 (C4), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx). On the other hand, T2 and T6 groups had the lowest malondialdehyde (MDA), glucose, and cortisol concentrations as well as alanine aminotransferase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH) enzyme levels when were compared with the control (P<0.05). After ammonia stress, fish in the supplemented groups, particularly T2 and T6, generally showed significantly higher values of lysozyme, ACH50, total Ig, NBT, MPO, C3, C4, SOD, CAT, GPx and lower levels of MDA, glucose, cortisol, ALT, ALP, LDH when compared with the control (P<0.05). In conclusion, a combined administration of RS and L. rhamnosus effectively improved growth performance and health status as well as enhanced the resistance of rainbow trout against ammonia toxicity.

Bioactive immunostimulants as health-promoting feed additives in aquaculture: A review

Bioactive immunostimulants could be derived from different sources like plants, animals, microbes, algae, yeast, etc. Bioactive immunostimulants are the most significant role to enhance aquatic production, as well as the cost of this method, which is effective, non-toxic, and environment-friendly. These immunostimulants are supportive to increase the immune system, growth, antioxidant, anti-inflammatory, and disease resistance of aquatic animals' health and also improve aquatic animal feed. Diseases are mainly targeted to the immune system of aquatic organisms in such a way that different processes of bioactive immunostimulants progress are considered imperative techniques for the development of aquaculture production. Communicable infections are the main problem for aquaculture, while the mortality and morbidity connected with some outbreaks significantly limit the productivity of some sectors. Aquaculture is considered the mainly developing food production sector globally. Protein insists is an important issue in human nutrition. Aquaculture has been an exercise for thousands of years, and it has now surpassed capture fisheries as the most vital source of seafood in the world. Limited study reports are available to focal point on bioactive immunostimulants in aquaculture applications. This review report provides information on the nutritional administration of bioactive immunostimulants, their types, functions, and beneficial impacts on aquatic animals' health as well as for the feed quality development in the aquaculture industry. The scope of this review combined to afford various kinds of natural derived bioactive molecules utilization and their beneficial effects in aquaculture applications.

Research Progress of the Gut Microbiome in Hybrid Fish

Fish, including hybrid species, are essential components of aquaculture, and the gut microbiome plays a vital role in fish growth, behavior, digestion, and immune health. The gut microbiome can be affected by various internal and/or external factors, such as host development, diet, and environment. We reviewed the effects of diet and dietary supplements on intestinal microorganisms in hybrid fish and the difference in the gut microbiome between the hybrid and their hybrids that originate. Then, we summarized the role of the gut microbiome in the speciation and ecological invasion of hybrid fish. Finally, we discussed possible future studies on the gut microbiome in hybrid fish, including the potential interaction with environmental microbiomes, the effects of the gut microbiome on population expansion, and fish conservation and management.

Physiological and histopathological alterations in Capoeta baliki and Squalius pursakensis after caused by some environmental pollutants

The present study was aimed to apply physiological and histological biomarkers of pelagic and benthic fish species as biomonitoring of environmental pollutants. Capoeta baliki and Squalius pursakensis were caught from 5 stations in Kirmir Stream (Turkey). After measuring the total length and weight for condition factor analysis, liver, gill, brain, and kidney tissues of fish were taken for histopathological analysis. Dorsal muscles of fish tissues were analyzed for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and polybrominated diphenyl ethers (PBDEs). The mean condition factor of C. baliki and S. pursakensis were 1.14 and 0.97, respectively. It was indicated that the first one was in good condition than the latter one. According to histopathological observations, the alterations in the tissues may be associated with the environmental pollutants' exposure. The total concentration of PAHs of dorsal muscle of C. baliki and S. pursakensis found ranged from 0.915 to 108.421 µg/kg and 0.601 to 675.248 µg/kg, respectively. The highest total concentrations of OCPs were found as 44.16 µg/kg for C. baliki and as 562.12 µg/kg for S. pursakensis. The PCB 28 (10.83 µg/kg), PCB 52 (10.92 µg/kg), PCB 138 (226.24 µg/kg), and the total concentrations of PBDEs were found as 151.74 µg/kg in only S. pursakensis. The result of the concentrations of the investigated pollutants was generally found higher in S. pursakensis which is a higher trophic level than C. baliki. Histopathological alterations were detected as hyperemia in liver, gill, and brain; as hydrophobic degeneration in liver; hyperplasia in gill; and tubular degeneration in kidney tissues of both species. The obtained result of the study shows that the environmental pollutants may affect the physiological and histological status of fish.

The ameliorative role of ascorbic acid against blood disorder, immunosuppression, and oxidative damage of oxytetracycline in rainbow trout (Oncorhynchus mykiss)

This experiment was aimed to determine the possible beneficial effects of dietary ascorbic acid (AA) on hematological indices, immune responses, and antioxidative capacity of Oncorhynchus mykiss treated with antibiotic oxytetracycline (OTC). A total of 150 fish were divided evenly among five experimental groups (30 fish of each, in 3 replicates) receiving diets containing OTC (0 and 100 mg per kg fish weight) and AA (100, 200, 400, and 800 mg per kg fish diet) for 28 days. Treatments include group A or control (100 mg AA without OTC), group B (100 mg AA with OTC), group C (200 mg AA with OTC), group D (400 mg AA with OTC), and group E (800 mg AA with OTC). The results obtained showed that the hematological indices (red blood cells, white blood cells, hematocrit, hemoglobin, and neutrophils), immunological parameters (plasma lysozyme, plasma complement, and skin mucus alkaline phosphatase activities), and antioxidant enzymes activities (superoxide dismutase and catalase) were significantly decreased by OTC in O. mykiss fed control diet (P < 0.05). The results also revealed that OTC significantly increased the activity of biochemical enzymes (aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase) in the plasma of O. mykiss fed control diet (P < 0.05). However, in comparison to the control diet, feeding fish with higher amounts of AA (400 and 800 mg/kg diet) significantly restored the hematological, immunological, and antioxidative responses in OTC-treated groups (p < 0.05). These findings show that the dietary supplementation of AA at 400 or 800 mg/kg diet is beneficial in relieving O. mykiss from OTC-induced oxidative stress and immunosuppression.

Oligosaccharides improve the flesh quality and nutrition value of Nile tilapia fed with high carbohydrate diet

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High-carbohydrate reduced muscle hardness and increased abdominal fat accumulation.

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Two oligosaccharides restored the fillet hardness of fish fed with high-carbohydrate diet.

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Galacto-oligosaccharides increased essential amino acids and delicious amino acids.

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Xylo-oligosaccharide promoted growth performance and alleviated fat accumulation.

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Oligosaccharides can be used as potential additives to regulate flesh quality.

High level of carbohydrate in aquafeed could achieve cost-sparing effect, but it may cause adverse effects on flesh quality of aquatic products. An eight-week trial was conducted to investigate whether oligosaccharides-supplementation, including Galacto-oligosaccharides (GOS) and xylo-oligosaccharide (XOS), could systematically improve the growth performance, texture characteristics and nutrition composition of Nile tilapia fed with high-carbohydrate diet. The results indicated that GOS-supplementation improved the amino acid composition, while XOS-supplementation showed beneficial effects on growth performance. High-carbohydrate diet had adverse effects on fillet texture, while oligosaccharide-supplementation regulated the expression of muscle development-related genes to help restoring muscle texture properties. Furthermore, either high-carbohydrate or addition of oligosaccharides could change the intestinal microbiota composition and their metabolites. Further correlation analysis suggested that intestinal microbiota may account for the improvement in fish growth condition and texture characteristics. Application of oligosaccharides may be an innovative strategy for flesh quality modulation in aquaculture.

Effectiveness of turmeric-enriched pellets to improve the immunity of Clarias batrachus toward motile Aeromonas septicemia disease

Background: Turmeric is known as a natural remedy to improve the immunity of organisms. This study aims to understand the effectiveness of turmeric-enriched pellets to improve the immunity of Clarias batrachus to Aeromonas hydrophila. Methods: The study was conducted from May to August 2020. C. batrachus fingerlings, 7-8 cm total length (TL) and 4-5 g (BW) at baseline, were kept in 30 L aquaria (10 fishes/aquarium; three replicated/treatment). Commercial pellets were mixed with turmeric powder. There were five treatment groups: P0 (control, no turmeric); P1 (0.5 g turmeric per Kg of pellets); P2 (0.7 g/Kg); P3 (0.9 g/Kg); Pp (positive control). Thirty days after being feed with turmeric-enriched pellets, all groups of fish were infected with 0.1 ml (10 ⁸) of A. hydrophila suspension, intramuscularly. The P0 group did not receive injection, while Pp group were not fed with turmeric-enriched pellets but were infected with the bacteria. Fourteen days after infection, clinical signs and hematology of the fish were studied. Results: Pp fish showed heavy clinical signs of A. hydrophila , such as loss of balance, pigmentation, hemorrhages and ulcers. P0 fish did not show any symptoms, while the treated fish reveled some clinical signs of A. hydrophila to a lesser extent than Pp, indicating that the fish is able to face the A. hydrophila attack. Hematology for Pp fish revealed high white blood cells, indicating that the fish were infected. The blood condition of the P0 fish, as well as those of the turmeric-treated fish were normal. In general, the P3 fish showed the least clinical signs of A. hydrophila and normal blood condition, indicating that P3 treatment is best. Conclusion: The best turmeric dosage to improve the immunity of C. batrachus toward A . hydrophila infection is 0.9 g/Kg pellets.

Effects of dietary yeast cell wall on biochemical indices, serum and skin mucus immune responses, oxidative status and resistance against Aeromonas hydrophila in juvenile Persian sturgeon (Acipenser persicus)

The present study aims to shed light on the effects of yeast cell wall (ImmunoWall®) supplementation on biochemical indices, oxidative status, serum and mucus immune responses as well as disease resistance of juvenile Persian sturgeon (Acipenser persicus). For this purpose, one hundred fifty three juvenile Persian sturgeons (47.78 ‏± 0.39 g) were distributed into nine tanks (500 L) and fed with basal diets containing two levels of yeast cell wall (YCW) 0.5% (T1) and 1% (T2) and a diet without YCW as control (0%). As shown by the results obtained at the end of 56-day feeding trial, YCW had no significant effect on glucose, cortisol, SGOT, lysozyme and IgM in serum (P > 0.05) albeit an enhancement of cholesterol, LDH, ALP and SOD and ACH50 was observed in fish fed YCW supplemented diets. However, plasma triglyceride levels were lower in fish fed YCW compared with the control group. Also, total protein content, lysozyme and protease activities in skin mucus were unaffected by the supplemented diets (P > 0.05) and only total immunoglobulin and ALP enzyme activity were significantly increased in T₁ and T₂ groups (P > 0.05). The cumulative mortality of the fish fed supplemented diets at the end of disease challenge was 100% where cumulative mortality of those fed the control diet was 75% (P < 0.05). The present study shows that increasing immune parameters in serum and mucus of juvenile Persian sturgeon by YCW dietary supplementation did not improve resistance against Aeromonas hydrophila. According to the obtained results, the YCW supplementation at 0.5 and 1% in the juvenile Persian sturgeon diet is not recommended.

Effects of Yu-Ping-Feng polysaccharides (YPS) on the immune response, intestinal microbiota, disease resistance and growth performance of Litopenaeus vannamei

A 28-day feeding trial was conducted to investigate the effects of Yu-Ping-Feng polysaccharides (YPS) containing Astragalus polysaccharides (APS), Atractylodes macrocephala polysaccharides (AMP) and Saposhnikoviae polysaccharides (SPS) on the immune response, intestinal microbiota, disease resistance and growth performance of Litopenaeus vannamei. Seven hundred and twenty shrimp (3.04 ± 0.33 g) were fed the following diets: Control, YPS1 (0.13% APS + 0.0325% AMP + 0.0325% SPS), YPS2 (0.13% APS + 0.0325% AMP + 0.065% SPS) and YPS3 (0.13% APS + 0.0325% AMP+0.0975% SPS). After 14 and 28 days of feeding, the immune responses of hemocytes and intestine were measured. Intestinal microbiota and growth performance were measured after 28 days of feeding, after that, a 7-day challenge test against Vibrio harveyi was conducted. A significant (P < 0.05) increase of the total haemocyte count (THC), phagocytic activity, antibacterial activity and phenoloxidase (PO) activity was observed in shrimp fed YPS diets compared to the control. Also, dietary YPS supplementation particularly YPS3 group significantly increased the expressions of immune-related genes in the hemocytes and intestine. Regarding the intestinal microbiota, the microbial diversity and richness decreased and functional genes associated with short-chain fatty acids metabolism increased in YPS groups. After Vibrio harveyi challenge, the cumulative mortality in YPS groups was significantly lower than that of the control. Besides, dietary YPS had no significant effect on growth performance of shrimp (P > 0.05). The present results suggested that YPS could be considered as potential prebiotics for aquaculture farmed shrimp.

Changes in the immune function of rainbow trout (Oncorhynchus mykiss) provide insights into strategies against BDE-47 stress

Polybrominated diphenyl ethers (PBDEs) are ubiquitous in marine ecosystems and have been suggested to bioaccumulate in aquatic food webs, with potentially negative impacts on marine organism. In this study, a 21-day experiment was performed under controlled laboratory conditions, in which 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), the most biotoxic PBDE in the marine environment, was fed to rainbow trout (Oncorhynchus mykiss) at concentrations of 50 and 500 ng g^-1 in the diet. BDE-47 significantly decreased the specific growth rate of O. mykiss and was highly concentrated in the liver and head kidney, as evidenced by increased bioaccumulation factor (BAF) values. Tissue observation revealed impairment of the microstructure of the head kidney. Important immune factors in the skin, blood and head kidney were significantly inhibited by BDE-47 treatment (p < 0.05), whereas the respiratory burst activity of macrophages was enhanced. Additionally, immune-related genes were strongly downregulated following BDE-47 exposure (p < 0.05). In a bacterial challenge, the treatment groups had much higher mortality than did the control group (p < 0.05). BDE-47 accumulated and impaired immune organs, and the hierarchy of immune responses was impaired, consequently reducing O. mykiss resistance to pathogen invasion.

Prebiotics and phytogenics functional additives in low fish meal and fish oil based diets for European sea bass (Dicentrarchus labrax): Effects on stress and immune responses

The use of terrestrial raw materials to replace fish meal (FM) and fish oil (FO) in marine fish diets may affect fish growth performance and health. In the last years functional additives have been profiled as good candidates to reduce the effects on health and disease resistance derived from this replacement, via reinforcement of the fish immune system. In the present study, three isoenergetic and isonitrogenous diets with low FM and FO (10% and 6% respectively) were tested based on supplementation either with 0.5% galactomannanoligosaccharides (GMOS diet) or 0.02% of a mixture of essential oils (PHYTO diet), a non-supplemented diet was defined as a control diet. Fish were fed the experimental diets in triplicate for 9 weeks and then they were subjected to a stress by confinement as a single challenge (C treatment) or combined with an experimental intestinal infection with Vibrio anguillarum (CI treatment). Along the challenge test, selected stress and immunological parameters were evaluated at 2, 24 and 168h after C or CI challenges. As stress indicators, circulating plasma cortisol and glucose concentrations were analyzed as well as the relative gene expression of cyp11b hydroxylase, hypoxia inducible factor, steroidogenic acute regulatory protein, heat shock protein 70 and heat shock protein 90 (cyp11b, hif-1α, StAR, hsp70 and hsp90). As immune markers, serum and skin mucus lysozyme, bactericidal and peroxidase activities were measured, as well as gene expression of Caspase-3 (casp-3) and interleukin 1β (il-1ß). The use of functional additives induced a significant (p < 0.05) reduction of circulating plasma cortisol concentration when confinement was the unique challenge test applied. Supplementation of PHYTO induced a down-regulation of cyp11b, hif-1α, casp-3 and il-1β gene expression 2h after stress test, whereas StAR expression was significantly (p < 0.05) up-regulated. However, when combination of confinement stress and infection was applied (CI treatment), the use of PHYTO significantly (p < 0.05) down-regulated StAR and casp-3 gene expression 2h after challenge test, denoting that PHYTO diet reinforced fish capacity of stress response via protection of head kidney leucocytes from stress-related apoptotic processes, with lower caspase-3 gene expression and a higher il-1β gene expression when an infection occurs. Additionally, dietary supplementation with GMOS and PHYTO compounds increased fish serum lysozyme after infection. Both functional additives entailed a better capability of the animals to cope with infection in European sea bass when fed low FM and FO diets.

Innate Immune Responses of Skin Mucosa in Common Carp (Cyprinus Carpio) Fed a Diet Supplemented with Galactooligosaccharides

Galactooligosaccharides (GOS) are well-known immunomodulatory prebiotics. We hypothesize that GOS supplemented in feed modulates innate immune responses in the skin-associated lymphoid tissue (SALT) of common carp. The aim of this study was to determine the impact of GOS on mRNA expression of the immune-related genes in skin mucosa. During the feeding trial, the juvenile fish (bodyweight 180 ± 5 g) were fed two types of diet for 50 days: control and supplemented with 2% GOS. At the end of the trial, a subset of fish was euthanized (n = 8). Skin mucosa was collected, and RNA was extracted. Gene expression analysis was performed with RT-qPCR to determine the mRNA abundance of the genes associated with innate immune responses in SALT, i.e., acute-phase protein (CRP), antimicrobial proteins (His2Av and GGGT5L), cytokines (IL1β, IL4, IL8, IL10, and IFNγ), lectin (CLEC4M), lyzosymes (LyzC and LyzG), mucin (M5ACL), peroxidase (MPO), proteases (CTSB and CTSD), and oxidoreductase (TXNL). The geometric mean of 40s s11 and ACTB was used to normalize the data. Relative quantification of the gene expression was calculated with ∆∆Ct. GOS upregulated INFγ (p ≤ 0.05) and LyzG (p ≤ 0.05), and downregulated CRP (p ≤ 0.01). We conclude that GOS modulates innate immune responses in the skin mucosa of common carp.

Dietary Approaches to Attain Fish Health with Special Reference to their Immune System

Fish despite their low collocation in the vertebrate phylum possess a complete immune system. In teleost fish both innate and adaptive immune responses have been described with melanomacrophage centers (MMCs) equivalent to mammalian germinal centers. Primary lymphoid organs are represented by the thymus and kidney, while spleen and mucosa-associated lymphoid tissues act as secondary lymphoid organs. Functions of either innate immune cells (e.g., macrophages and dendritic cells) or adaptive immune cells (T and B lymphocytes) will be described in detail, even including their products, such as cytokines and antibodies. In spite of a robust immune arsenal, fish are very much exposed to infectious agents (marine bacteria, parasites, fungi, and viruses) and, consequentially, mortality is very much enhanced especially in farmed fish. In fact, in aquaculture stressful events (overcrowding), microbial infections very frequently lead to a high rate of mortality. With the aim to reduce mortality of farmed fish through the reinforcement of their immune status the current trend is to administer natural products together with the conventional feed. Then, in the second part of the present review emphasis will be placed on a series of products, such as prebiotics, probiotics and synbiotics, β-glucans, vitamins, fatty acids and polyphenols all used to feed farmed fish. With special reference to polyphenols, results of our group using red grape extracts to feed farmed European sea bass will be illustrated. In particular, determination of cytokine production at intestinal and splenic levels, areas of MMCs and development of hepatopancreas will represent the main biomarkers considered. All together, our own data and those of current literature suggests that natural product administration to farmed fish for their beneficial effects may, in part, solve the problem of fish mortality in aquaculture, enhancing their immune responses.

Enhanced mucosal immune responses, immune related genes and growth performance in common carp (Cyprinus carpio) juveniles fed dietary Pediococcus acidilactici MA18/5M and raffinose

The present study was conducted to evaluate the effects of dietary Pediococcus acidilactici (PA) and raffinose (RF) alone or in combination on growth performance, mucosal immune factors and immune related genes expression in common carp (Cyprinus carpio) juveniles. Fish with initial weight of 10.0 ± 2.5 g were fed the following experimental diets for 60 days: control (without supplementation), prebiotic (2 g RF kg^-1 diet), probiotic (6 × 10⁸ CFU g^-1PA) and synbiotic (2 g RF kg^-1+ 6 × 10⁸ CFU g^-1PA). Carp fed synbiotic and probiotic diets had the highest (19.53 ± 0.16) and the lowest (18.05 ± 0.65) final body weight, respectively and the other experimental groups showed intermediate values. Singular administration of PA or in combination with 2 g RF kg^-1 significantly increased skin mucus total immunoglobulin (Ig) and protein compared other groups, meanwhile, values of skin mucus protease activity enhanced by dietary immunostimulants administration in comparison with the control (P < 0.05). The expression of gene encoding lysozyme in skin pronouncedly increased by supplementing diets with singular or mixture of PA and RF; however, the expression of intestinal lysozyme gene as well as tumor necrosis factor-α genes expression in skin and intestine were not affected by administrating different immunostimulants (P > 0.05). The highest growth performance was noticed in fish fed synbiotic (P < 0.05). Overall, the combination of 2 g RF kg^-1 with 6 × 10⁸ CFU g^-1PA is recommended for improving immunological responses of C. carpio juveniles.

Effect of alkoxy glycerol on growth performance, immune response and disease resistance in Nile Tilapia (Oreochromis niloticus)

Fish oil and their compounds derived from the same have immense applications in the improvement of health, brain development, enhancing immunity etc. This study aimed at the supplementation of such a compound alkoxy glycerol derived from shark liver oil in fish diet and thereby analyzing growth as well as immune parameters of Oreochromis niloticus. 400 fishes were distributed into 11 glass tanks, and then fishes were weighed before starting the experiment. (Average weight was found to be 5.3 ± 0.10 g). Feed was prepared using alkoxy glycerol in the doses like 5, 10, 15 g kg^-1 Fishes were fed with the prepared diet for 30 days and growth parameters like specific growth rate (SGR), weight gain (WG), final weight (FW), and feed conversion ratio (FCR) were measured. On the 30th day, fishes were challenged with 0.1 ml of normal saline solution containing 10⁷ CFUml^-1 of Aeromonas hydrophila and disease resistance was monitored. After 30 days of post challenge observation, immunological and lipid peroxidation assays like alternative complement (ACH50), phagocytosis (PI), respiratory burst activities (RB), and serum lysozyme (SL) were performed.

Skin mucus metabolites in response to physiological challenges: A valuable non-invasive method to study teleost marine species

Knowledge concerning the health and welfare of fish is important to conserve species diversity. Fish mucosal surfaces, and particularly the skin, are of utmost importance to protect the integrity and homeostasis of the body and to prevent skin infections by pathogens. We performed three trials simulating different environmental and anthropogenic challenges: fish capture (air exposure), bacterial infection and fasting, with the aim of evaluating epidermal mucus as a non-invasive target of studies in fish. In this initial approach, we selected three well-known marine species: meagre (Argyrosomus regius), European sea bass (Dicentrarchus labrax) and gilthead sea bream (Sparus aurata) for our study. Mucus viscosity was measured in order to determine its rheological properties, and mucus metabolite (glucose, lactate, protein and cortisol) levels were analysed to establish their suitability as potential biomarkers. Skin mucus appeared as a viscous fluid exhibiting clearly non-Newtonian behaviour, with its viscosity being dependent on shear rate. The highest viscosity (p < 0.05) was observed in sea bream. Mucus metabolites composition responded to the different challenges. In particular, glucose increased significantly due to the air exposure challenge in meagre; and it decreased during food deprivation in sea bream by a half (p < 0.05). In contrast, mucus protein only decreased significantly after pathogenic bacterial infection in sea bass. In addition, mucus lactate immediately reflected changes closely related to an anaerobic condition; whereas cortisol was only modified by air exposure, doubling its mucus concentration (p < 0.05). The data provided herein demonstrate that mucus metabolites can be considered as good non-invasive biomarkers for evaluating fish physiological responses; with the glucose/protein ratio being the most valuable and reliable parameter. Determining these skin mucus metabolites and ratios will be very useful when studying the condition of critically threatened species whose conservation status prohibits the killing of specimens.

Effects of orange peels derived pectin on innate immune response, disease resistance and growth performance of Nile tilapia (Oreochromis niloticus) cultured under indoor biofloc system

The present study investigates the effects of orange peels derived pectin (OPDP) on skin mucus and serum immune parameters, disease resistance and growth performance of O. niloticus cultured under indoor biofloc system. Six hundred Nile tilapia (average weight 9.09 ± 0.05 g) were distributed into 15 fiber tanks (300 L per tank) assigned to five treatments repeated in triplicate. Fish were fed experimental diets contain different levels OPDP as follows: 0 (control in clear water), 0 (control in biofloc system), 5, 10, and 20 g kg^-1 OPDP for 8 weeks. At weeks 4 and 8 post feeding, skin mucus lysozyme (SMLA), peroxidase activities (SMPA), serum lysozyme (SL), serum peroxidase (SP), alternative complement (ACH50), phagocytosis (PI), and respiratory burst activities (RB) as well specific growth rate (SGR), weight gain (WG), final weight (FW), and feed conversion ratio (FCR) were measured. Also, resistance against Streptococcus agalactiae was assessed after 8 weeks post-feeding. Nile tilapia fed OPDP supplemented diets had significantly higher SMLA and SMPA compared to the controls (P < 0.05). The maximum values were observed in tilapia fed 10 g kg^-1 OPDP followed by 5 and 20 g kg^-1 OPDP. Nevertheless, no significant differences were observed between these two supplemented diets and between the control groups (P > 0.05). Regarding the serum immunological parameters, dietary inclusion of 10 g kg^-1 OPDP showed significant higher SL and PI than other supplemented groups and control groups (P < 0.05). However, no significant differences were observed in SL and PI of fish fed 5 and 20 g kg^-1 OPDP (P > 0.05). Dietary administration of OPDP significantly increased SP and ACH50 compared to the controls (P < 0.05), regardless of inclusion level. Additionally, non-significant change was found in RB of OPDP fed fish when compared with the controls (P > 0.05). The challenge test revealed that relative percent of survival (RPS) in OPDP treatments were 45.45%, 81.82%, 50%, respectively. The highest RPS was noticed in fish fed 10 g kg^-1 OPDP. Furthermore, dietary administration of OPDP significantly improved SGR, WG, FW, and FCR (P < 0.05). Overall, the present findings suggested that OPDP can be taken into account as functional feed additives for O. niloticus.

Combined effects of dietary low molecular weight sodium alginate and Pediococcus acidilactici MA18/5M on growth performance, haematological and innate immune responses of Asian sea bass (Lates calcalifer) juveniles

Six weeks feeding trial was conducted to examine the effects of dietary administration of low molecular weight sodium alginate (LMWSA) and Pediococcus acidilactici MA 18/5M (PA) on humoral and mucosal immune responses, haematological parameters and growth performance, of Lates calcarifer juveniles. Fish (12.0 ± 0.2 g) were fed experimental diets as follows: Control (diet 1, basal diet), 5 g kg^-1 LMWSA (diet 2), 10 g kg^-1 LMWSA (diet 3), 0.9 × 10⁷ CFU g^-1 PA (diet 4), 5 g kg^-1 LMWSA + 0.9 × 10⁷ CFU g^-1 PA (Diet 5), and 10 g kg^-1 LMWSA + 0.9 × 10⁷ CFU g^-1 PA (Diet 6). Results indicated a significant (P < 0.05) increase in innate immune parameters including serum lysozyme, bactericidal, hemolytic and respiratory burst activities as well as mucosal immune responses including lysozyme and bactericidal activities, when diet was supplemented with immunostimulants. Moreover, the combined effects of LMWSA with PA resulted in more pronounced immunological responses compared to the control and singular administration. Red and white blood cell counts significantly increased with either singular or combined administration of LMWSA and PA compared with the control group (P < 0.05). The singular administration of PA and combined supplementation of 5 g kg^-1 LMWSA with PA significantly increased growth performance and feed intake compared with other experimental groups (P < 0.05). These results indicated that combined administration of LMWSA and PA can be considered as beneficial feed additive and immunostimulant in L. calcarifer juveniles.

The functionality of prebiotics as immunostimulant: Evidences from trials on terrestrial and aquatic animals

The gut immune system is, the main option for maintaining host's health, affected by numerous factors comprising dietary constituents and commensal bacteria. These dietary components that affect the intestinal immunity and considered as an alternative of antibiotics are called immunosaccharides. Fructooligosaccharide (FOS), Galactooligosaccharide (GOS), inulin, dietary carbohydrates, and xylooligosaccharide (XOS) are among the most studied prebiotics in human as well as in aquaculture. Although prebiotics and probiotics have revealed potential as treatment for numerous illnesses in both human and fish, a comprehensive understanding of the molecular mechanism behind direct and indirect effect on the intestinal immune response will help more and perhaps extra effective therapy intended for ailments. This review covers the most newly deep-rooted scientific outcomes about the direct and indirect mechanism through which these dietetic strategies can affect intestinal immunity of terrestrial and aquatic animals. Prebiotics exert an influence on gut immune system via the increase in lysozyme and phagocytic activity, macrophage activation and stimulation of monocyte-derived dendritic cells. Furthermore, these functional molecules also enhance epithelial barrier function, beneficial gut microbial population, and production of intermediate metabolites for example short chain fatty acids (SCFAs) that assist in balancing the immune system. Moreover, emphasis will be sited on the relationship among food/feed, the microbiota, and the gut immune system. In conclusion, further studies are nonetheless essential to confirm the direct effect of prebiotics on immune response.

The effects of dietary supplement of galactooligosaccharide on innate immunity, immune related genes expression and growth performance in zebrafish (Danio rerio)

The present study investigates the effect of different levels of galactooligosaccharide (GOS) on innate immune parameters, immune related genes expression as well as growth performance in zebrafish (Danio rerio). Four hundred and twenty fish (mean weight 45 ± 0.1 mg) were supplied, randomly stocked in twelve aquaria assigned to four treatments. Zebrafish were fed with either control diet or control diet enriched with different levels (0.5, 1 and 2%) of GOS for eight weeks. At the end of feeding trial innate immune parameters (total immunoglobulin, total protein and alkaline phosphatase activity), immune related genes expression (interleukin 1 beta [il1b], Lysozyme [lyz], tumor necrosis factor alpha [tnf-alpha]) as well as growth performance were measured. Evaluation of immune parameters revealed significant (P < .05) increase of total protein and total Ig in zebrafish fed 1 or 2% GOS compared other treatments. However, in case of lysozyme activity no significant (P > .05) differences were noticed between GOS fed fish and control group. Also, in case of ALP activity, significant increase (P < .05) was observed in 2% GOS treatment. Gene expression studies revealed significant upregulation (P < .05) of tnf-alpha and lyz genes in GOS fed fish. While no significant (P > .05) difference was observed in case of il1b gene expression. Evaluation of growth performance at the end of feeding trial revealed no significant (P < .05) improvement in GOS fed groups. The present results revealed positive effects of GOS on innate immune parameters and related gene expression in zebrafish.

Effects of dietary raffinose on growth, non-specific immunity, intestinal morphology and microbiome of juvenile hybrid sturgeon (Acipenser baeri Brandt ♀ × A. schrenckii Brandt ♂)

This study was performed to determine the efficacy of raffinose on the growth, non-specific immunity, intestinal morphology and microbiota of juvenile hybrid sturgeon, (Acipenser baeri Brandt ♀ × A. schrenckii Brandt ♂). Hybrid sturgeons were divided into 2 groups and each group was fed with diets supplemented with or without raffinose for 56 days. Hybrid sturgeon fed diet supplemented with raffinose had significantly higher final body weight (FBW), specific growth rate (SGR), and weight gain ratio (WGR) than fish fed the control diet (P < 0.05). Raffinose in diet had no negative effect on feed intake (FI) and feed conversion ratio (FCR) (P > 0.05). Compared with the control diet, the myeloperoxidase (MPO) and respiratory burst (NBT) activitives were significantly higher in sturgeon fed the raffinose supplemented diet (P < 0.05). The increasing of intestinal villi area and mucosal folds were observed in intestinal tract of sturgeon when they fed the raffinose supplemented diet. Meanwhile, the residual bait of intestinal tract was relatively lower in sturgeon with raffinose treatment. High-throughput sequencing revealed that majority of reads derived from the sturgeon digesta were constituted by members of Proteobacteria, Firmicutes, Fusobacteria and Actinobacteria. Shannon's diversity index existed significant difference among dietary treatments indicating that the overall microbial community was modified to a large extent by dietary raffinose. In conclusion, supplementation of the diet with raffinose is capable of improving hybrid sturgeon growth performances and intestinal morphology, modifying the intestinal microbial composition.

Effects of synbiotics on immunity and disease resistance of narrow-clawed crayfish, Astacus leptodactylus leptodactylus (Eschscholtz, 1823)

The aim of this study was to evaluate the effects of prebiotics (mannanoligosaccharide and xylooligosaccharide), probiotics (Enterococcus faecalis and Pediococcus acidilactici) and synbiotics for 126 days on the immune responses, hemolymph indices, antioxidant enzymes, and biological responses after a 48-hour Aeromonas hydrophila exposure of sub-adult crayfish (11.45 ± 1.87 g). Most antibacterial activities were observed in the shell mucus of crayfish fed a diet containing xylooligosaccharide + E. faecalis and mannanoligosaccharide + Pediococcus acidilactici against Nocardia brasilience and Vibrio harveyi (p < 0.05). Feeding crayfish a xylooligosaccharide + E. faecalis diet increased protein levels and the activities of alkaline phosphatase and lysozyme in the shell mucus after the feeding trial and 48 h after the A. hydrophila-injection challenge (p < 0.05). The highest ratio of the lactobacillus count to the total viable count was observed in synbiotic diets (p < 0.05). Feeding crayfish a xylooligosaccharide + E. faecalis diet increased the growth rate and the resistance to the A. hydrophila-injection challenge (p < 0.05). These results revealed that feeding crayfish with synbiotic diets was more effective than a single administration with prebiotics and probiotics.