Fish Immunity Research Articles

Effects of replacing fish meal with biofloc meal on growth performance, nutrients metabolism, immune response and intestinal microbiota of common carp (Cyprinus carpio)

This study investigated the effects of replacing fish meal (FM) with biofloc meal (BM) on the growth, digestion function, protein metabolism, lipid metabolism, immunity, antioxidant capacity and intestinal microbiota of common carp (Cyprinus carpio). The experiment includes two trials (a growth trial and a digestibility trial). In the growth trial, the control diet contained 20% FM. And five isonitrogenous and isolipidic diets were formulated to replace 0% (CK), 20% (BM20), 40% (BM40), 60% (BM60) and 80% (BM80) of the FM protein with BM. The five diets were fed to common carp (3.73 ± 0.01 g) for 56 days. The results indicated that the growth performance [final weight (FW), specific growth rate (SGR) and feed efficiency ratio (FER)] and digestive enzymes activities displayed a noteworthy quadratic trend with the increasing replacement level of FM with BM (P < 0.05), reaching a maximum at the BM40 group and a minimum at the BM80 group. Regression analysis of weight gain rate (WGR) against the substitution level found that the optimal level of BM replacing FM was 34.12%. The appropriate levels of BM could improve protein metabolism and lipid metabolism by regulating the expressions of related genes. Regarding the expression levels of PI3K, mTOR and HSL mRNA, they were the highest in the BM40 group and the lowest in the BM80 group, while the levels of ACC and FAS mRNA were reversed (P < 0.05). Simultaneously, the number of lipid vacuoles in the BM80 group were significantly increased than the CK group. Replacing 40% FM with BM augmented the fish immunity and antioxidant capacity, as showed by elevated the C3, C4 and IgM levels as well as CAT and SOD activities, and reduced the expression levels of NF-κB, TNF-α and Keap1 (P < 0.05). Regarding intestinal microbiota, replacing 40% FM with BM could improve the intestinal microbiota structure. The digestibility trial results showed that the apparent digestibility of protein and lipid in BM of common carp was slightly lower than FM. Conclusively, replacing 40% FM with BM could promote growth, immunity and protein metabolism of common carp, but excessive substitution level (80%) could compromise growth and hepatopancreas health.

The effects of two dietary synbiotics on growth performance, hematological parameters, and nonspecific immune responses in Japanese Eel.

Feed additives have attracted increased attention in aquaculture due to their ability to modulate fish gut microbiota, resulting in improved fish growth and immunity. This study assessed the effects of two synbiotics in Japanese Eel Anguilla japonica: Bacillus subtilis with mannooligosaccharides (MOS) and Enterococcus faecium with fructooligosaccharides (FOS). Six diets, including a control (CON) diet, oxytetracycline (OTC) diet, and four synbiotic diets (B. subtilis at 1 × 106 or 1 × 107 colony-forming units [CFU]/g with MOS at 5 g/kg [BS6MO and BS7MO; collectively, BSMOS diets] and E. faecium at 1 × 106 or 1 × 107 CFU/g with FOS at 5 g/kg [EF6FO and EF7FO; collectively, EFFOS diets]), were fed to triplicate groups of 20 fish (average weight ± SD = 6.00 ± 0.07 g) for 8 weeks. Fish fed the BSMOS diets showed significantly higher weight gain, specific growth rate (SGR), and feed efficiency compared to fish fed the CON and OTC diets, but the values were not significantly different from those of fish fed the EFFOS diets. Weight gain and SGR of fish that were given EFFOS diets were not significantly different from those of fish fed all other diets. Fish fed the OTC diet showed a higher mean aspartate aminotransferase level, although the difference was not statistically significant. The myeloperoxidase activity of fish fed the BS7MO diet was significantly higher than those of fish receiving all other diets, and the superoxide dismutase activity of fish fed the BS7MO diet was also significantly higher than that of fish fed the EF7FO diet. Overall, the BSMOS synbiotic diets were significantly more effective than the CON diet in enhancing fish survival against a Vibrio anguillarum challenge. Our findings suggest that synbiotics can be a preferable alternative to antibiotics in aquaculture.

Unraveling the immune functions of large yellow croaker Tmem208 in response to Pseudomonas plecoglossicida: Insights from cloning, expression profiling, and transcriptome analysis

Pseudomonas plecoglossicida, the causative agent of Visceral White Spot Disease, poses substantial risks to large yellow croaker (Larimichthys crocea) aquaculture. Previous genome-wide association studies (GWAS), directed towards elucidating the resistance mechanisms of large yellow croaker against this affliction, suggested that the transmembrane protein 208 (named Lctmem208) may confer a potential advantage. TMEM proteins, particularly TMEM208 located in the endoplasmic reticulum, plays significant roles in autophagy, ER stress, and dynamics of cancer cell. However, research on TMEM's function in teleost fish immunity remains sparse, highlighting a need for further study. This study embarks on a comprehensive examination of LcTmem208, encompassing cloning, molecular characterization, and its dynamics in immune function in response to Pseudomonas plecoglossicida infection. Our findings reveal that LcTmem208 is highly conserved across teleost species, exhibiting pronounced expression in immune-relevant tissues, which escalates significantly upon pathogenic challenge. Transcriptome analysis subsequent to LcTmem208 overexpression in kidney cells unveiled its pivotal role in modulating immune-responsive processes, notably the p53 signaling pathway and cytokine-mediated interactions. Enhanced phagocytic activity in macrophages overexpressing LcTmem208 underscores its importance in innate immunity. Taken together, this is the first time reported the critical involvement of LcTmem208 in regulating innate immune responses of defensing P. plecoglossicida, thereby offering valuable insights into teleost fish immunity and potential strategies for the selective breeding of disease-resistant strains of large yellow croaker in aquaculture practices.

The regulation of prolactin secretion and its targeting function of teleost

Prolactin is involved in regulating various physiological activities of vertebrates and is one of the most momentous pituitary hormones. However, not enough attention is currently paid to prolactin, especially in teleost. This paper aims to gather, organize, and analyze recent studies on the regulation and functions of prolactin. By comparing with other animal groups, it highlights the significant role of prolactin in fish reproduction, immunity, growth, and osmotic pressure regulation, as well as the upstream and downstream factors that may be involved in the regulation of prolactin functions were introduced to provide a theoretical basis for the in-depth study and potential practical application of prolactin.

Evaluation of the efficacy of MONTANIDE™ GR01, a new adjuvant for feed-based vaccines, on the immune response and protection against Streptococcus agalactiae in oral vaccinated Nile tilapia (Oreochromis niloticus) under laboratory and on-farm conditions

Streptococcosis, an emerging infectious disease caused by Streptococcus agalactiae, has had adverse effects on farmed tilapia. Several vaccines have been developed to prevent this disease and induce a specific immune response against S. agalactiae infection. In this study the use of MONTANIDE™ GR01, a new adjuvant for oral vaccination, was optimized for use in tilapia under laboratory and field studies. In the laboratory trial the immune response and protective efficacy of two doses of MONTANIDE™ GR01, 20 % (w/w) and 2 % (w/w), included into the feed-based adjuvanted vaccines were assessed comparatively. Following immunization, the innate immune parameters studied in serum, including lysozyme, myeloperoxidase, catalase and glutathione peroxidase activity, were all increased significantly. Furthermore, specific IgM antibodies against S. agalactiae were induced significantly in serum post-vaccination, with higher levels observed in both groups that received the feed-based adjuvanted vaccine. Under both injection and immersion challenge conditions, the relative percent survival for the feed-based adjuvanted vaccine groups ranged from 78 % to 84 %. Following use of the low dose concentration of MONTANIDE™ GR01 for oral vaccination of tilapia in cage culture systems, several innate immune parameters were effectively enhanced in the immunized fish. Similarly, the levels of specific IgM antibodies in the serum of feed-based vaccinated fish were significantly enhanced, reaching their highest levels 2–5 months post-vaccination. Cytokines associated with innate and adaptive immunity were also examined, and the expression levels of several genes showed significant up-regulation. This indicates that both cellular and humoral immune responses were induced by the feed-based adjuvanted vaccine. The economic impact of a feed-based adjuvanted vaccine was examined following vaccination, considering the growth performance and feed utilization of the fish. It was found that the Economic Performance Index and Economic Conversion Ratio were unaffected by vaccination, further demonstrating that there are no negative impacts associated with administering a feed-based vaccine to fish. In conclusion, the data from this study indicate that MONTANIDE™ GR01 is a highly valuable adjuvant for oral vaccination, as demonstrated by its ability to induce a strong immune response and effectively prevent streptococcal disease in Nile tilapia.

Galectin-8-like isoform X1 mediates antibacterial, antiviral, and antioxidant responses in red-lip mullet (Planiliza haematocheilus) through positive modulation of pro-inflammatory cytokine, chemokine, and enzymatic antioxidant activity

Galectin 8 belongs to the tandem repeat subclass of the galectin superfamily. It possesses two homologous carbohydrate recognition domains linked by a short peptide and preferentially binds to β-galactoside-containing glycol-conjugates in a calcium-independent manner. This study identified Galectin-8-like isoform X1 (PhGal8X1) from red-lip mullet (Planiliza haematocheilus) and investigated its role in regulating fish immunity. The open reading frame of PhGal8X1 was 918bp, encoding a soluble protein of 305 amino acids. The protein had a theoretical isoelectric (pI) point of 7.7 and an estimated molecular weight of 34.078 kDa. PhGal8X1 was expressed in various tissues of the fish, with prominent levels in the brain, stomach, and intestine. PhGal8X1 expression was significantly (p < 0.05) induced in the blood and spleen upon challenge with different immune stimuli, including polyinosinic:polycytidylic acid, lipopolysaccharide, and Lactococcus garvieae. The recombinant PhGal8X1 protein demonstrated agglutination activity towards various bacterial pathogens at a minimum effective concentration of 50 μg/mL or 100 μg/mL. Subcellular localization observations revealed that PhGal8X1 was primarily localized in the cytoplasm. PhGal8X1 overexpression in fathead minnow cells significantly (p < 0.05) inhibited viral hemorrhagic septicemia virus (VHSV) replication. The expression levels of four proinflammatory cytokines and two chemokines were significantly (p < 0.05) upregulated in PhGal8X1 overexpressing cells in response to VHSV infection. Furthermore, overexpression of PhGal8X1 exhibited protective effects against oxidative stress induced by H2O2 through the upregulation of antioxidant enzymes. Taken together, these findings provide compelling evidence that PhGal8X1 plays a crucial role in enhancing innate immunity and promoting cell survival through effective regulation of antibacterial, antiviral, and antioxidant defense mechanisms in red-lip mullet.

Pleurotus eryngii root waste and soybean meal co-fermented protein improved the growth, immunity, liver and intestinal health of largemouth bass (Micropterus salmoides)

The present study aimed to evaluate the effect of king oyster mushroom (Pleurotus eryngii) root waste and soybean meal co-fermented protein (CFP) on growth performance, feed utilization, immune status, hepatic and intestinal health of largemouth bass (Micropterus salmoides). Largemouth bass (12.33 ± 0.18 g) were divided into five groups, fed with diets containing 0 %, 5 %, 10 %, 15 % and 20 % CFP respectively for 7 weeks. The growth performance and dietary utilization were slightly improved by the supplementation of CFP. In addition, improved immunoglobulin M (IgM) content and lysozyme activity in treatments confirm the enhancement of immunity in fish by the addition of CFP, especially in fish fed 20 % CFP (P < 0.05). Furthermore, CFP significantly improved liver GSH (glutathione) content in groups D10 and D15 (P < 0.05), and slightly improved total antioxidant capacity (T-AOC), superoxide dismutase (SOD) activity while slightly reduced malondialdehyde (MDA) content. Simultaneously, the upregulation of lipolysis-related genes (PPARα, CPT1 and ACO) expression and downregulation of lipid synthesis-related genes (ACC and DGAT1) expression was recorded in the group D20 compared with the control (P < 0.05), which were consistent with the decreased liver lipid contents, suggests that lipid metabolism was improved by CFP. In terms of intestinal structural integrity, ameliorated intestinal morphology in treatments were consistent with the upregulated Occludin, Claudin-1 and ZO-1 genes expression. The intestinal pro-inflammatory cytokines (TNF-α and IL-8) expression were suppressed while the anti-inflammatory cytokines (IL-10 and TGF-β) were activated in treatments. The expression of antimicrobial peptides (Hepcidin-1, Piscidin-2 and Piscidin-3) and intestinal immune effectors (IgM and LYZ) were slightly up-regulated in treatments. Additionally, the relative abundance of intestinal beneficial bacteria (Firmicutes) increased while the relative abundance of potential pathogenic bacteria (Fusobacterium and Proteobacteria) decreased, which indicated that the intestinal microbial community was well-reorganized by CFP. In conclusion, dietary CFP improves growth, immunity, hepatic and intestinal health of largemouth bass, these data provided a theoretical basis for the application of this novel functional protein ingredient in fish.

Significance of dietary quinoa husk (Chenopodium quinoa) in gene regulation for stress mitigation in fish

The persistent challenges posed by pollution and climate change are significant factors disrupting ecosystems, particularly aquatic environments. Numerous contaminants found in aquatic systems, such as ammonia and metal toxicity, play a crucial role in adversely affecting aquaculture production. Against this backdrop, fish feed was developed using quinoa husk (the byproduct of quinoa) as a substitute for fish meal. Six isonitrogenous diets (30%) and isocaloric diets were formulated by replacing fish meal with quinoa husk at varying percentages: 0% quinoa (control), 15, 20, 25, 30 and 35%. An experiment was conducted to explore the potential of quinoa husk in replacing fish meal and assess its ability to mitigate ammonia and arsenic toxicity as well as high-temperature stress in Pangasianodon hypophthalmus. The formulated feed was also examined for gene regulation related to antioxidative status, immunity, stress proteins, growth regulation, and stress markers. The gene regulation of sod, cat, and gpx in the liver was notably upregulated under concurrent exposure to ammonia, arsenic, and high-temperature (NH3 + As + T) stress. However, quinoa husk at 25% downregulated sod, cat, and gpx expression compared to the control group. Furthermore, genes associated with stress proteins HSP70 and DNA damage-inducible protein (DDIP) were significantly upregulated in response to stressors (NH3 + As + T), but quinoa husk at 25% considerably downregulated HSP70 and DDIP to mitigate the impact of stressors. Growth-responsive genes such as myostatin (MYST) and somatostatin (SMT) were remarkably downregulated, whereas growth hormone receptor (GHR1 and GHRβ), insulin-like growth factors (IGF1X, IGF2X), and growth hormone gene were significantly upregulated with quinoa husk at 25%. The gene expression of apoptosis (Caspase 3a and Caspase 3b) and nitric oxide synthase (iNOS) were also noticeably downregulated with quinoa husk (25%) reared under stressful conditions. Immune-related gene expression, including immunoglobulin (Ig), toll-like receptor (TLR), tumor necrosis factor (TNFα), and interleukin (IL), strengthened fish immunity with quinoa husk feed. The results revealed that replacing 25% of fish meal with quinoa husk could improve the gene regulation of P. hypophthalmus involved in mitigating ammonia, arsenic, and high-temperature stress in fish.

Strain-Specific Benefits of Bacillus Probiotics in Hybrid Grouper: Growth Enhancement, Metabolic Health, Immune Modulation, and Vibrio harveyi Resistance.

In the realm of modern aquaculture, the utilization of probiotics has gained prominence, primarily due to their ability to enhance growth, boost immunity, and prevent diseases in aquatic species. This study primarily investigates the efficacy of Bacillus subtilis strains, both host-derived and from other sources, in influencing fish growth, immunity, lipid metabolism, and disease resistance. Employing a 42-day feeding trial, we divided hybrid grouper into four distinct groups: a control group on a basal diet and three experimental groups supplemented with 1 × 108 CFU/g of different Bacillus subtilis strains-BS, 6-3-1, and HAINUP40. Remarkably, the study demonstrated that the 6-3-1 and HAINUP40 groups exhibited significant enhancements across key growth parameters: final body weight (FBW), weight gain rate (WGR), feed intake (FI), feed efficiency ratio (FER), and feed conversion ratio (FCR). The investigation into lipid metabolism revealed that the 6-3-1 strain upregulated seven metabolism-related genes, HAINUP40 affected four metabolism-related genes, and the BS strain influenced two metabolism-related genes, indicating diverse metabolic impacts by different strains. Further, a notable reduction in liver enzymes AST and ALT was observed across all supplemented groups, implying improved liver health. Noteworthy was the BS strain's superior antioxidative capabilities, positively affecting all four measured parameters (CAT, GSH-Px, MDA). In the sphere of immune-related gene expression, the BS strain significantly decreased the expression of both inflammation and apoptosis-related genes, whereas the HAINUP40 strain demonstrated an upregulation in these genes. The challenge test results were particularly telling, showcasing improved survival rates against Vibrio harveyi infection in the BS and 6-3-1 groups, unlike the HAINUP40 group. These outcomes highlight the strain-specific nature of probiotics and their varying mechanisms of action within the host. In conclusion, this study reveals that probiotic strains, varying by source, demonstrate unique, strain-specific effects in promoting growth and modulating immunity in hybrid grouper. This research highlights the promise of tailored probiotic applications in improving aquaculture practices. Such advancements contribute to more sustainable and efficient fish farming methods.

Interleukin-6 receptor (IL-6R) is involved in the innate immune response of olive flounder (Paralichthys olivaceus) to resist pathogens

The immunity of bony fish depends on the conserved components and functional complexity of immune cytokines. Herein, we used the pleiotropic cytokine IL-6 receptor as a target gene to study the defense response of PoIL-6R resist pathogens in different immune tissues of olive flounder, we found that PoIL-6R is widely expressed in these tissues studied and shows a significant immune response after stimulation with bacteria in vivo. In addition, we found a broad-spectrum immune response of PoIL-6R to bacterial and pathogen-associated molecular patterns through in vitro stimulation of olive flounder embryonic cell lines (FEC), and further revealed the function of PoIL-6R in positively regulating the natural immunity of olive flounder through activation of the NF-κB signaling pathway by overexpression of PoIL-6R in FEC. Collectively, these results demonstrate for the involvement of interleukin-6 receptors in the innate immune response of olive flounder to resist pathogens, and provides new perspectives and theoretical foundations for assessing the evolutionary mechanisms of adaptive immunity in vertebrates.

The melano-macrophage: The black leukocyte of fish immunity

Melanin and the process of melanin synthesis or melanogenesis have central roles in the immune system of insects, and production of melanin-synthesizing enzymes from their haemocytes may be induced following activation through danger signals. Melanin-containing macrophage-like cells have been extensively studied in amphibians and they are also present in reptiles. In fish, melano-macrophages are especially recognized with respect to melano-macrophage centres (MMCs), hypothesized to be analogues of germinal centres in secondary lymphoid organs of mammals and some birds. Melano-macrophages are in addition present in several inflammatory conditions, in particular melanised focal changes, or black spots, in the musculature of farmed Atlantic salmon, Salmo salar. Melanins are complex compounds that may be divided into different forms which all have the ability to absorb and scatter light. Other functions include the quenching of free radicals and a direct effect on the immune system. According to the common view held in the pigment cell community, vertebrate melanin synthesis with melanosome formation may only occur in cells of ectodermal origin. However, abundant information suggests that also myeloid cells of ectothermic vertebrates may be classified as melanocytes. Here, we discuss these opposing views and review relevant literature. Finally, we review the current status on the research concerning melanised focal muscle changes that represent the most severe quality problem in Norwegian salmon production, but also other diseases where melano-macrophages play important roles.

Expression of immuno-transcriptome response in red hybrid tilapia (Oreochromis sp.) hindgut following vaccination with feed-based bivalent vaccine.

Streptococcosis and aeromoniasis are the main obstacles to sustainable tilapia production. Vaccination offered an effective method to control microbial infections. Previously, a feed-based bivalent vaccine (FBBV) containing killed whole organisms of Streptococcus agalactiae and Aeromonas hydrophila mixed with 10% palm oil was successfully developed, which provided good protection against streptococcosis and aeromoniasis in Oreochromis sp. However, the mechanisms of immunities in vaccinated fish still need clarification. Here, the hindgut transcriptome of vaccinated and control fish was determined, as the gut displays higher affinity towards antigen uptake and nutrient absorption. The efficacy of FBBV to improve fish immunity was evaluated according to the expression of immune-related genes in the vaccinated fish hindgut throughout the 8-week experimental period using RT-qPCR. The vaccinated fish hindgut at week 6 was further subjected to transcriptomic analysis due to the high expression of immune-related genes and contained killed whole organisms. Results demonstrated the expression of immune-related genes was in correlation with the presence of killed whole organisms in the vaccinated fish hindgut. Transcriptomic analysis has allowed the prediction of robust immune-related pathways, including innate and adaptive immunological responses in vaccinated fish hindgut than control fish. Pathways related to the regulation of lipid metabolism and modulation of the immune system were also significantly enriched (p ≤ .05). Overall, results offer a fundamental study on understanding the immunological response in Oreochromis sp. following vaccination with the FBBV pellet and support further application to prevent bacterial diseases in aquaculture.

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.

Enhancement of Skin Mucus Immunity, Carotenoid Content, Sexual Parameters, and Growth Response in Guppy Fish (Poecilia reticulata) Fed with Green Algae (Chaetomorpha aerea) Diets

The research aimed to analyze the influences of adding marine green algae Chaetomorpha aerea to the diet of guppy fish (Poecillia reticulate) on growth, immunological responses in skin mucus, total carotenoid content, and sexual characteristics. A total of 450 fish, with a mean body weight of 0.19 ± 0.1 g and 30 fish per tank (triplicate), were randomly fed into 15 experimental tanks, each containing 50 L. Five different diets with 0, 1, 2, 4, 8, and 10% of C. aerea g/kg diets were fed to P. reticulate for 30 days. After 30 days, growth, immunological responses in skin mucus, total carotenoid content, and sexual characteristics were investigated. The results observed that the feed conversion rate and fry output were significantly (p &gt; 0.05) decreased in experimental groups compared to the control group. The results revealed that the dietary inclusion of C. aerea algal significantly increased (p &lt; 0.05) in mucosal immunological parameters containing lysozyme activity, myeloperoxidase activity, total immunoglobulins, and alternative complement activity, which were the highest in the group with 4% of C. aerea g/kg. Additionally, lateral skin and the caudal fin of fish had higher total carotenoid levels from the dietary C. aerea algae diet than the control group, which were the highest in the groups with 4%. Among them, 4 and 8% of C. aerea g/kg diet resulted in better growth performance and feed conversion ratio. Thus, the study suggested that 4% of C. aerea g/kg diet has enrichment of immunity, total carotenoid concentrations, and skin mucus immunity of P. reticulate.

The role of adaptive resistance in a widespread freshwater mussel species

Abstract Organism features, such as size, weight, sex and age, among others, can influence the success of parasitism. For species that depend on a host to complete their life cycle, such as freshwater mussels (Bivalvia, Unionida), understanding how these traits influence parasitism can help guide management actions aimed at improving their reproductive success, ultimately benefitting their conservation. In this study, the physiological compatibility between the duck mussel Anodonta anatina and its host fish was investigated in a simultaneous infestation experiment on four (three native and one non‐native) fish species using sympatric and allopatric host strains. The success of glochidia metamorphosis in juvenile mussels was evaluated as a function of host species, strain and fish length. Successful metamorphosis was achieved in almost all fish species tested and differences were detected between allopatric and sympatric strains, with higher values found in allopatric hosts. Allopatric strains of primary hosts produce more juveniles than marginal hosts and non‐native species. In addition, larger fish have lower rates of metamorphosis. The results confirm recent findings showing high variation in the metamorphosis success of A. anatina glochidia among different native and non‐native hosts, both in the natural environment and in artificial laboratory infestations. Allopatric hosts were more suitable for encystment, demonstrating potential adaptive immunity, not yet observed in A. anatina. Nevertheless, A. anatina may temporarily exploit the naivety of smaller fish regardless of strain. Overall, the results suggest that mussel propagation, reproduction and reintroduction efforts should consider the mechanisms that influence adaptive immunity in fish, including differences in compatibility within and between populations of sympatric and allopatric host strains. This situation should be taken into account, as successful metamorphosis is an important factor in the selection of hosts for juvenile development, especially in efforts to propagate endangered mussel species.

Optimal dietary lipid levels alleviated adverse effects of high temperature on growth, lipid metabolism, antioxidant and immune responses in juvenile turbot (Scophthalmus maximus L.)

Fish physiological health is often negatively impacted by high-temperature environments and there are few studies on how dietary lipids affect fish growth and physiology when exposed to heat stress. The main objective of this research was to examine the impact of dietary lipid levels on growth and physiological status of juvenile turbot (Scophthalmus maximus L.) and determine if dietary lipid concentration could alleviate the possible adverse effects of heat stress. Five diets containing 6.81%, 9.35%, 12.03%, 14.74%, and 17.08% lipid, respectively, were formulated and fed to turbot (initial weight 5.13 ± 0.02 g) under high-temperature conditions (24.0–25.0 °C). Meanwhile, the diet with 12.03% lipid (considered by prior work to be an optimal dietary lipid level) was fed to turbot of the same size at normal temperature. Results suggested that, among the different dietary lipid levels under high-temperature conditions, fish fed the optimal lipid (12.03%) exhibited better growth compared to non-optimal lipid groups, as evidenced by higher weight gain and specific growth rate. Simultaneously, the optimal lipid diet may better maintain lipid homeostasis, as attested by lower liver and serum lipid, along with higher liver mRNA levels of lipolysis-related genes (pgc1α, lipin1, pparα, lpl and hl) and lower levels of synthesis-related genes (lxr, fas, scd1, pparγ, dgat1 and dgat2). Also, the optimal lipid diet might mitigate oxidative damage by improving antioxidant enzyme activity, decreasing malondialdehyde levels, and up-regulating oxidation-related genes (sod1, sod2, cat, gpx and ho-1). Furthermore, the optimal lipid may enhance fish immunity, as suggested by the decrease in serum glutamic-oxalacetic/pyruvic transaminase activities, down-regulation of pro-inflammatory genes and up-regulation of anti-inflammation genes. Correspondingly, the optimal lipid level suppressed MAPK signaling pathway via decreased phosphorylation levels of p38, JNK and ERK proteins in liver. In summary, the optimal dietary lipid level facilitated better growth and physiological status in turbot under thermal stress.

Fermentation in aquafeed processing: Achieving sustainability in feeds for global aquaculture production

AbstractImproving feed suitability and bolstering the global upsurge in fish production is a strategic challenge for aquaculture. The utilization of plant and animal derived ingredients in aquafeed for achieving sustainable in finfish aquaculture is affected by various factors, including the presence of antinutritional factors, lowered nutrient bioavailability, indigestible particles and microbial contaminants. Applying fermentation to overcome these problems in aquafeed ingredients has received considerable attention in recent years as fermentation provides health‐promoting probiotic benefits to host organisms. Fermentation has also been shown in many studies to improve nutrient availability and bioavailability of feed, increased palatability and digestibility and eliminate anti‐nutritional compounds in dietary feed ingredients, making them more easily digestible which eventually improve growth and health performance of fish. Therefore, it is imperative to accelerate the use of fermented feedstuffs as aquafeed if sustainable aquaculture is to be achieved. This review reported the various methods of fermentation, characteristics of fermented feed ingredients, factors that are considered during fermentation and overall nutritional quality of fermented feed ingredients for aquaculture production. The role of fermented feed ingredients for various farmed species in terms of growth, feed utilization, gut microbiota composition, immunity and disease resistance in fish is thoroughly discussed. The possible drawbacks associated with the fermentation process are also discussed in the article.

Probiotic performance of B. subtilis MS. 45 improves aquaculture of rainbow trout Oncorhynchus mykiss during acute hypoxia stress

The aim of this study was to produce mutant strains of Bacillus subtilis with high probiotic performance for use in the aquaculture of rainbow trout Oncorhynchus mykiss. The main strain of B. subtilis (MS) was irradiated with gamma rays (5.3 KGy). Subsequently, the B. subtilis mutant strain no. 45 (MS. 45) was selected for bacterial growth performance, resistance to acidic conditions, resistance to bile salts and antibacterial activity against Aeromonas hydrophila and Pseudomonas fluorescens. After 60 days, the rainbow trout (70.25 ± 3.89 g) fed with MS. 45 and MS were exposed to hypoxia stress (dissolved oxygen = 2 ppm). Subsequently, immune indices (lysozyme, bacterial activity and complement activity), hematological indices [hematocrit, hemoglobin, WBC, RBC, mean corpuscular volume (MCV)] and antioxidant factors (T-AOC, SOD and MDA)) were analyzed after and before hypoxia exposure. The expression of immunological genes (IFN-γ, TNF-α, IL-1β, IL-8) in the intestine and the expression of hypoxia-related genes (HIF-1α, HIF-2α, FIH1) in the liver were compared between the different groups under hypoxia and normoxia conditions. Growth, immunological and antioxidant indices improved in group MS. 45 compared to the other groups. Stress indices and associated immunologic and hypoxia expressions under hypoxia and normoxia conditions improved in MS. 45 compared to the other groups. This resulted in improved growth, immunity and stress responses in fish fed with the microbial supplement of MS. 45 (P < 0.05) under hypoxia and normoxia conditions, (P < 0.05), resulting in a significant improvement in trout aquaculture.

Effect of temperature fluctuation on the physiological stress response of hybrid pearl gentian grouper during waterless keeping alive.

Temperature fluctuations are inevitable and have an important impact on the survival of fish during transportation. Therefore, the effect of temperature fluctuation (15 ± 1 °C, 15 ± 2 °C, 15 ± 3 °C) on the muscle quality, physiological, and immune function of hybrid pearl gentian grouper before waterless keeping alive, during keeping alive (0 h, 3 h, 6 h, 9 h, 12 h), and after revival for 12 h was investigated. The plasma glucose concentration of grouper gradually decreased to 0.645 ± 0.007 mg/mL, 0.657 ± 0.006 mg/mL, and 0.677 ± 0.004 mg/mL after keeping alive for 12 h under different temperature fluctuations of 15 ± 1 °C, 15 ± 2 °C, and 15 ± 3 °C, respectively. The cortisol concentration and lysozyme activity of pearl gentian grouper significantly increased (P < 0.05) during the keeping alive period. The results suggested that fish bodies would produce acute stress response, strengthen immune defense ability, and quickly consume a lot of energy to adapt to the low-temperature anhydrous environment. In all treatment groups, the activities of plasma alanine transaminase (ALT) and aspartate aminotransferase (AST) and the content of creatinine gradually increased with the prolongation of the survival time. The hardness and springiness of muscle decreased from 5965.99 ± 20.15 and 0.90 ± 0.00 to 3490.69 ± 27.59 and 0.42 ± 0.01, respectively. In the meanwhile, the change of glycogen and lactic acid content was opposite, indicating that temperature fluctuation harmed the liver, kidney function, and muscle quality. In the later stage of keeping alive, the superoxide dismutase (SOD) and catalase (CAT) activities decreased, especially in the temperature fluctuation group of ±3 °C (125.99 ± 5.48 U/mgprot, 44.21 ± 0.63 U/mgprot), leading to an imbalance of fish immunity. In summary, higher temperature fluctuation would influence the physiological function and immune defense ability and decrease the quality of pearl gentian grouper.

Are fish immunocompetent enough to face climate change?

Ongoing climate change has already been associated with increased disease outbreaks in wild and farmed fish. Here, we evaluate the current knowledge of climate change-related ecoimmunology in teleosts with a focus on temperature, hypoxia, salinity and acidification before exploring interactive effects of multiple stressors. Our literature review reveals that acute and chronic changes in temperature and dissolved oxygen can compromise fish immunity which can lead to increased disease susceptibility. Moreover, temperature and hypoxia have already been shown to enhance the infectivity of certain pathogens/parasites and to accelerate disease progression. Too few studies exist that have focussed on acidification, but direct immune effects seem to be limited while salinity studies have led to contrasting results. Likewise, multi-stressor experiments essential for unravelling the interactions of simultaneously changing environmental factors are still scarce. This ultimately impedes our ability to estimate to what extent climate change will hamper fish immunity. Our review about epigenetic regulation mechanisms highlights the acclimation potential of the fish immune response to changing environments. However, due to the limited number of epigenetic studies, overarching conclusions cannot be drawn. Finally, we provide an outlook on how to better estimate the effects of realistic climate change scenarios in future immune studies in fish.