Search Results (21)

Background/Objectives: Nocardia seriolae and Aeromonas veronii are two important pathogens that can affect a wide range of fish species and cause substantial economic losses. However, a vaccine that simultaneously protects fish from these two bacterial infections is not yet available. Methods: Three formalin-inactivated whole-cell vaccines prepared from N. seriolae and A. veronii (Monovalent Av, Monovalent Ns and Bivalent Av-Ns) were generated, and their efficacy was evaluated through a range of tests. The immune-related gene expression in the spleen and head kidney, enzyme activity, and specific antibody levels in serum were also detected. Results: All groups of vaccinated fish exhibited increased serum enzymatic activity compared with control fish, which peaked at week 3 after vaccination; in particular, that of the Bivalent Av-Ns group increased remarkably. The expression of immune-related genes in the spleen, head, and kidneys increased after immunization and were significantly enhanced (p < 0.05) in the bivalent vaccine group. Specific antibodies were produced at the 1st wpv, peaked at the 4th to the 5th wpv, and then decreased at the 6th wpv in all vaccinated groups. The Monovalent Av and Monovalent Ns against A. veronii and N. seriolae showed 56.67% and 22.22% RPS, respectively. Moreover, Bivalent Av-Ns offered 33.33% and 76.67% RPS for single infection with N. seriolae or A. veronii, as well as providing 44.44% RPS for dual infection with combined N. seriolae and A. veronii. Conclusions: Our findings indicate that the administration of the A. veronii and N. seriolae bivalent vaccine can protect largemouth bass from both bacterial infections. Full article

The present study investigates the gut microbiota dynamics of Micropterus salmoides during Nocardia seriolae infection and identifies potential probiotic candidates for disease control in aquaculture. We artificially infected M. salmoides with N. seriolae and analyzed the gut microbiota of dying fish, asymptomatic fish during the peak mortality period, and healthy fish. The results showed that N. seriolae infection significantly altered the gut microbiota diversity. Based on analysis of gut microorganisms, we isolated and identified an N. seriolae-resistant Bacillus from the gut of M. salmoides, which was named B. amyloliquefaciens MS05 (BaMS05). BaMS05 demonstrated significant antibacterial activity against N. seriolae and other common pathogens of M. salmoides both in vitro and in vivo. Additionally, BaMS05 could colonize the gut of M. salmoides for at least five days and exhibited a protective effect against N. seriolae infection, reducing cumulative mortality by 40% at the fifth day. This study provides insights into the role of gut microbiota in disease resistance and highlights BaMS05 as a potential probiotic for preventing and controlling N. seriolae infections in aquaculture. Further research will focus on optimizing the application of BaMS05 and verifying its biosafety for practical use in M. salmoides farming. Full article

The liver of fish is an essential metabolic organ that also serves an immune regulatory role. In this study, we constructed a model of largemouth bass (Micropterus salmoides) infected with Nocardia seriolae by injection to explore the immune and antioxidant functions of the liver. The results showed that N. seriolae infection caused severe pathological changes in the liver, including cell necrosis, granuloma formation, and leukocyte infiltration. The level of mRNA expression of immune-related genes in the liver was significantly increased 2 days post-infection. Moreover, the combined analysis of transcriptome and metabolome showed that N. seriolae infection markedly affected liver metabolism, including glutathione metabolism, arginine and proline metabolism, arachidonic acid metabolism, as well as starch and sucrose metabolism. Additionally, multiple key biomarkers were identified as involved in regulating responses to N. seriolae infection, including arginine, glutathione, gpx, GST, PLA2G, GAA, and PYG. To further elucidate the regulatory effects of arginine on the immune and antioxidant processes in the liver, primary hepatocytes were isolated and cultured. The results demonstrated that arginine supplementation significantly reduced the expression of LPS-induced apoptosis-related genes (bax, cas3, cas8, and cas9) by up to 50% while increasing the expression of antioxidant genes (gpx, GST) by up to 700% at 24 h. Through the analysis of metabolic changes and immune responses in the liver following N. seriolae infection, combined with in-vitro experiments, this study elucidated the anti-apoptotic and antioxidant effects of arginine, revealing the immune response mechanisms in fish liver and laying the groundwork for using nutritional strategies to improve fish health. Full article

The large yellow croaker (Larimichthys crocea), one of the most economically valuable marine fish species in China, suffers significant economic losses in aquaculture due to infectious diseases caused by marine pathogens, such as Nocardia seriolae. The pathogenic mechanisms underlying N. seriolae infection in L. crocea and the host immune responses remain inadequately characterized. To investigate the molecular mechanisms of this infection, we conducted transcriptome sequencing on the head kidney tissues of L. crocea at 1, 3, 7, and 14 days post-infection with N. seriolae. In total, 421, 1052, 3215, and 2459 upregulated genes, along with 1853, 1777, 3718, and 3134 downregulated genes were identified, respectively. KEGG enrichment analysis revealed that differentially expressed genes were predominantly associated with immune and metabolic pathways. Notably, pathways involved in Toll-like receptor signaling, ECM–receptor interaction, cytokine–cytokine receptor interaction, and focal adhesion were significantly enriched, highlighting an immune response to N. seriolae infection in L. crocea. In addition, significant enrichment of the citrate cycle (TCA cycle) and oxidative phosphorylation pathways in metabolic processes suggests an upregulated ATP synthesis to meet the heightened energy demand associated with the immune response to infection. These findings contribute to a deeper understanding of the immune defense mechanisms in the head kidney of L. crocea against N. seriolae infection and elucidate aspects of N. seriolae pathogenicity. Full article

Background/Objectives: The interleukin 17 (IL-17) family, known for its proinflammatory properties, is important in immune responses against bacterial and fungal infections. To exert its immune function, the IL-17 family typically binds to IL-17 receptor (IL-17R) to facilitate signal transduction. Methods: This study identified, cloned and analyzed seven IL-17 and nine IL-17R family members in snakeheads. Results: A duplication event occurred in snakehead IL-17s and IL-17Rs, but bioinformatics analyses indicated that these genes were conserved in both protein domains and evolutionary processes. Tissue distribution analysis revealed that IL-17s/IL-17Rs were widely distributed in the detected tissues, with relatively high expression levels in immune tissues. Upon Nocardia seriolae stimulation, most members were expressed, particularly IL-17C2, IL-17D, IL-17N, IL-17RA1, IL-17RA2, IL-17RC1, and IL-17RE1, which were significantly upregulated in gill and intestine. Conclusions: These results suggested that IL-17s and IL-17Rs played a crucial role in mucosal immunity against bacterial infection, providing insights into immunoprophylactic strategies for bacterial diseases in aquaculture. Full article

The typical clinical signs of Nocardia seriolae infection include white nodules, ranging from 0.1 to 10 mm in diameter, distributed across various internal organs. However, the structural composition of nodules of different sizes remains unexplored. In this study, natural cases of largemouth bass (Micropterus salmoides) were collected, and pathogenic bacteria were isolated and confirmed through a re-infection experiment. The isolated bacteria were identified as N. seriolae through 16S rRNA and gyrB gene sequencing. Healthy largemouth bass were infected with the isolate using an immersion infection and observed continuously over 56 days. Samples were successfully obtained from the incubation, prodromal, symptomatic, and convalescent phases, allowing for gross, histological, and ultrastructural observations of nodular lesion progression. Results demonstrated two types of nodular lesions: necrotic foci and granulomas. Macroscopically visible nodules larger than 1 mm, observed primarily in the liver, spleen, kidney, and muscle tissues of moribund fish, exhibited coagulative necrosis and were identified as the principal cause of mortality. Conversely, granulomas, with diameters less than 1 mm, were consistently present in the spleen, kidney, and liver during the symptomatic and convalescent phases. Full article

Fish possess lipases from embryonic development to adulthood. Lipase activity methods vary and significantly differ in terms of the concentration of the substrate used, bile salt, Ca²⁺, temperature, pH, and type of lipase units, which limits comparative studies. The three most-used substrates are p-nitrophenyl (p-NP), β-naphthyl (β-N) derivates, and emulsified natural oils. These were selected to be redesigned in this study to measure lipase activity under temperature, pH, ion, and bile salt conditions closer to fish physiology, using the appropriate molar absorption coefficient to calculate the lipase units. Cynoscion parvipinnis (CP), Seriola rivoliana (SR), Centropomus viridis (CV), Elop affinis (EA), and Canthidermis maculate (CM) pyloric caeca-intestine extracts were studied. Sodium taurocholate showed the highest activity for intestinal lipases, and the fatty acid length in the substrates changed the lipase hydrolysis rate. The highest lipase activity was obtained with p-NP butyrate and p-NP caprylate in four fish species. Lipase activity was highly activated with Ca²⁺ (4–7 mM). The β-N absorption spectrum indicates a plateau between 534 and 554 nm for fish lipases. Salmon oil was identified as the most digestible lipid in the four fish species using the in vitro digestibility assay. The lipase zymogram showed an apparent size of 46.3 kDa for CP, 40.2 kDa for SR, 46.2 kDa for CM, 106.6 kDa for EA, and 58.3, 84.6, and 162.1 kDa for CV. Full article

Effectively treating and preventing outbreaks is crucial for improving the economic benefits of aquaculture. Therefore, utilizing immunostimulants, either alone or in combination, is regarded as a promising strategy. In this study, β-glucan + APS (200 mg/kg + 200 mg/kg), β-glucan (200 mg/kg), APS (200 mg/kg), enrofloxacin (15 mg/kg), and sulfadiazine (15 mg/kg) were added to feed to assess the effects against Nocardia seriolae infection in largemouth bass (Micropterus salmoides) within 14 days. The survival rates did not differ between the enrofloxacin group and the β-glucan + APS group, but both were significantly higher than that of the control group. Additionally, the enrofloxacin group and the β-glucan + APS group exhibited the lowest bacterial loads and tissue damage. Importantly, the β-glucan + APS treatment significantly improved serum enzyme activities (total superoxide dismutase, lysozyme, total protein) and the expression of immune genes (IL-1β, TNF-α, IFN-γ, IgM) compared to the other treatment groups. The enrofloxacin group showed similar efficacy to the β-glucan + APS group in combating N. seriolae infection, but N. seriolae in the enrofloxacin group developed drug resistance. In summary, the combined use of β-glucan and APS is a promising strategy for treating bacterial diseases, thereby contributing to the promotion of sustainable aquaculture development. Full article

To clarify the population genetic structure, intrapopulation diversity, and interpopulation differentiation of yellowtail kingfish (Seriola aureovittata), we sampled 143 individuals from five collections of yellowtail kingfish: farmed (n = 30) and wild (n = 33) collections in China, a wild collection in Japan (n = 20), and farmed (n = 31) and wild (n = 29) collections in Australia. Using 2b-RAD simplified genome sequencing, we obtained an average of 287,594 unique tags per population, with an average sequencing depth of 27.13×. Our final genotype dataset included 48,710 SNPs (Single Nucleotide Polymorphisms). The five collections were all in Hardy–Weinberg equilibrium, and the interpopulation differentiation varied among the sample collections. The genetic differentiation coefficients (Fst) between the Chinese and Japanese yellowtail kingfish collections were low and the gene flow (Nm) values were high. These results suggest continuous gene flow occurs frequently between the collections, indicating that they belong to the same population. In contrast, genetic differentiation was high between the Australian collections and the Chinese and Japanese populations, suggesting different evolutionary origins and belonging to different populations. The farmed and wild Australian collections fell into distinct clades in a neighbor-joining phylogeny tree, suggesting farmed fish have begun to differentiate from the wild collection. A similar level of genetic diversity between the wild collections in China and Japan suggests that they originated from the same spawning ground. This, therefore, reminds us that in future aquaculture processes attention is needed regarding implementing targeted breeding strategies. In addition, our data will contribute to Chinese yellowtail kingfish genetic breeding and the sustainable use of Chinese yellowtail kingfish germplasms. Full article

The fillets and roes of 29 species of dry-salted fishes consumed in Eurasian countries were analyzed for fatty acids (FAs), tocols, and squalene, looking for derived health benefits. FAs were analyzed by GC-FID, and tocols and squalene were analyzed by HPLC-DAD. With some exceptions, docosahexaenoic (DHA, 22:6n-3), eicosapentaenoic (EPA, 20:5n-3), and arachidonic (ARA, 20:4n-6) acids were the prominent polyunsaturated fatty acids (PUFAs). The fillets of Scardinius erythrophthalmus reached the highest amounts of total FAs, ARA, and DHA (23.1, 1.82, and 2.49 mg/100 g). The fillets of Seriola quinqueradiata showed the highest percentages of DHA (34.4% of total FAs). Nutritional quality indices for fish lipids were favorable in all samples, especially the n-6/n-3 PUFA ratio, which was below 1 in most cases. α-Tocopherol was found in all fillets and roes, especially in Cyprinidae and Pleuronectidae species, and the highest value was found in the roes of Abramis brama (5.43 mg/100 g). Most samples contained tocotrienols at trace levels. The fillets of Clupeonella cultriventris contained the highest amounts of squalene (1.83 mg/100 g). Overall, dry-salted fish stand out due to their high concentrations of ARA, EPA, and DHA, as well as for α-tocopherol concentrations in roes. Full article

In this study, we investigated the effect of dietary curcumin on non-specific immune responses and antioxidative ability in Seriola dumerili under ammonia stress and post-recovery. Three diets were prepared to contain 0, 75, and 150 mg/kg of curcumin. A total of 225 greater amberjack (initial weight: 100.90 ± 0.03 g) were distributed into nine cylindrical tanks, constituting an experimental design with three treatments and three replicates. After 56 days of feeding, plasma, intestinal, and hepatic enzyme activities were evaluated. Then, an acute ammonia challenge experiment was conducted. Ten fish per tank were subjected to acute ammonia stress (total ammonia-N: 1000 mg/L) for eight minutes followed by six minutes of recovery. The results indicated that dietary curcumin significantly promoted intestinal and hepatic alkaline phosphatase (ALP) and acid phosphatase (ACP) levels as well as hepatic antioxidative enzymes such as superoxide dismutase (SOD), total antioxidant capacity (T-AOC), reduced glutathione (GSH), and glutathione peroxidase (GSH-Px) of greater amberjack. In addition, curcumin addition improved the activities of antioxidant enzymes, such as SOD, T-AOC, GSH, GSH-Px, and catalase (CAT), and reduced malondialdehyde (MDA) content in liver, spleen, head kidney, and brain tissues after post-recovery. The indexes related to immunity and antioxidant enzymes in the liver, gill, and spleen rose again to some extent, but they showed the worst recovery ability in the head kidney and brain tissue samples. These results indicate that dietary curcumin supplementation could increase non-specific immune responses, antioxidant ability, and enhance resistance to high ammonia stress in juvenile S. dumerili. Full article

This study investigated the effects of added eugenol on water quality and the metabolism and antioxidant capacity of the liver and gills of the greater amberjack (Seriola dumerili) during simulated transport. The juvenile fish (10.34 ± 1.33 g) were transported in sealed plastic bags containing different eugenol concentrations at a density of 24.79 kg/m³ for 8 h. The different eugenol concentrations were divided into five groups: 0 μL/mL (control group), 0.0125 μL/mL, 0.025 μL/mL, 0.0375 μL/mL, and 0.05 μL/mL, with three replicates of each. The results showed that 0.05 μL/mL of eugenol could significantly increase dissolved oxygen, but 0.025 μL/mL–0.0375 μL/mL resulted in a significant decrease in dissolved oxygen and significant increases in NH₄⁺-N and NO₂⁻-N. It was found that 0.05 μL/mL of eugenol caused significant up-regulation of the relative expression of CPT-1 in the liver, significant down-regulation of the relative expression of FAS and PK in the liver and gills, a significant increase in glycogen concentration, and a significant decrease in glucose concentration. This suggests that 0.05 μL/mL of eugenol could reduce the metabolic capacity of fish. In addition, 0.05 μL/mL of eugenol caused significant up-regulation of the relative expression of CAT and a significant decrease of MDA concentration in the liver. Meanwhile, the gills showed significant up-regulation of CAT relative expression, significant down-regulation of Keap1 relative expression, and a significant increase in GSH activity, resulting in a significant increase in MDA concentration when the concentration of eugenol reached or exceeded 0.025 μL/mL. This suggests that 0.05 μL/mL eugenol could improve the antioxidant capacity of fish and lipid peroxidation levels in the gills. In conclusion, the addition of 0.05 μL/mL eugenol could improve water quality, and the metabolic and antioxidant capacities of liver and gills, but it could also increase lipid peroxidation levels in the gills under transport conditions. Full article

Arachidonic acid (ARA, 20:4n-6) fed to Seriola dorsalis juveniles at different levels was evaluated. After a seven-week feeding trial, growth performance, hepatopancreas and muscle fatty acid (FA) composition, expression of lipid-relevant genes, and blood parameters were evaluated. Four isoproteic and isolipidic experimental diets were formulated to contain 44% crude protein and 11% lipids with graded inclusion levels of ARA, 0% (Control), 0.4, 0.9, and 1.4% of the total diet. S. dorsalis juveniles (14.54 ± 0.18 g) were randomly divided into twelve tanks with fifteen animals each. The animals were hand fed three times per day to apparent satiation. Dietary treatments did not significantly affect the growth performance, SGR, FCR, and feed intake of fish. Different levels of ARA in the experimental diets directly influenced liver and muscle FA profiles, with significant changes in ARA and EPA deposition between Control treatment and 1.4%, in both tissues. The expression of arachidonate 5-lipoxygenase (alox5), acyl-CoA dehydrogenase very long chain (acadvl), carnitine O-palmitoyltransferase 1(cpt1a) was significantly affected by dietary treatments, with an expression increasing accordingly to the increasing ARA levels. In contrast, a reduction of fatty acid synthase (fas) and proliferator-activated receptor alpha (ppara) expression was significantly reduced as ARA increased in the diet. In addition, a significant reduction in blood cortisol and glucose was found at a 0.9% ARA level compared to the other treatments. Based on the performance, cortisol levels, the gene expression for eicosanoids synthesis, and lipid metabolic pathways, the present study suggests a maximum ARA inclusion of 0.9% in diets for California yellowtail juveniles, S. dorsalis. Full article

The age and growth of fish populations is a critical issue for stock assessment, population dynamics and fishery management. Spawner biomass, mortality, growth, recruitment and age at maturity can be misconstrued if the age estimator is inaccurate. Age can be estimated by annuli count, but this requires expertise and is expensive. Otolith weight (OW) is a good indicator of how long a fish has lived, because OW increases during an individual’s life. Seriola lalandi is a migratory fish and is an important resource for local fishermen in northern Chile. Aspects of its biology, i.e., age and growth, remain unknown, at least for the population annually arriving in northern Chile. Fish of a known age (n = 105; from 5.5 to 25.7 cm in FL) from yellowtail aquaculture facilities at Universidad de Antofagasta allowed us to estimate the growth rate of OW, and fish obtained from local fishermen (n = 71; from 37.9 to 109 cm in FL) allowed us to estimate the age and growth of S. lalandi from the analysis of OW, without the need for calibration. The following four models were fitted with the known ages and fork lengths: the von Bertalanffy growth function, the Gompertz and logistic models and the seasonalized von Bertalanffy growth function. The latter model showed the best adjustment (according to the Akaike information criterion) with the following parameters: L_∞, 98.58 cm.; K, 0.59; t₀, 0.07; t_s, 0.84; and C, 0.97. Full article

The environmental characteristics of the Taiwan Strait (TS) have been linked to variations in the abundance and distribution of greater amberjack (Seriola dumerili) populations. Greater amberjack is a commercially and ecologically valuable species in ecosystems, and its spatial distribution patterns are pivotal to fisheries management and conservation. However, the relationship between the catch rates of S. dumerili and the environmental changes and their impact on fish communities remains undetermined in the TS. The goal of this study was to determine the spatiotemporal distribution pattern of S. dumerili with environmental characteristics in the TS from south to north (20°N–29°N and 115°E–127°E), applying generalized additive models (GAMs) and spatiotemporal fisheries data from logbooks and voyage data recorders from Taiwanese fishing vessels (2014–2017) as well as satellite-derived remote sensing environmental data. We used the generalized linear model (GLM) and GAM to analyze the effect of environmental factors and catch rates. The predictive performance of the two statistical models was quantitatively assessed by using the root mean square difference. Results reveal that the GAM outperforms the GLM model in terms of the functional relationship of the GAM for generating a reliable predictive tool. The model selection process was based on the significance of model terms, increase in deviance explained, decrease in residual factor, and reduction in Akaike’s information criterion. We then developed a species distribution model based on the best GAMs. The deviance explained indicated that sea surface temperature, linked to high catch rates, was the key factor influencing S. dumerili distributions, whereas mixed layer depth was the least relevant factor. The model predicted a relatively high S. dumerili catch rate in the northwestern region of the TS in summer, with the area extending to the East China Sea. The target species is strongly influenced by biophysical environmental conditions, and potential fishing areas are located throughout the waters of the TS. The findings of this study showed how S. dumerili populations respond to environmental variables and predict species distributions. Data on the habitat preferences and distribution patterns of S. dumerili are essential for understanding the environmental conditions of the TS, which can inform future priorities for conservation planning and management. Full article