Hypoxia is a globally pressing environmental problem in aquatic ecosystems. In the present study, a comprehensive analysis was performed to evaluate the effects of hypoxia on physiological responses (hematology, cortisol, biochemistry, hif gene expression and the HIF pathway) of hybrid sturgeons (Acipenser schrenckii ♂ × Acipenser baerii ♀). A total of 180 hybrid sturgeon adults were exposed to dissolved oxygen (DO) levels of 7.00 ± 0.2 mg/L (control, N), 3.5 ± 0.2 mg/L (moderate hypoxia, MH) or 1.00 ± 0.1 mg/L (severe hypoxia, SH) and were sampled at 1 h, 6 h and 24 h after hypoxia. The results showed that the red blood cell (RBC) counts and the hemoglobin (HGB) concentration were significantly increased 6 h and 24 h after hypoxia in the SH group. The serum cortisol concentrations gradually increased with the decrease in the DO levels. Moreover, several serum biochemical parameters (AST, AKP, HBDB, LDH, GLU, TP and T-Bil) were significantly altered at 24 h in the SH group. The HIFs are transcription activators that function as master regulators in hypoxia. In this study, a complete set of six hif genes were identified and characterized in hybrid sturgeon for the first time. After hypoxia, five out of six sturgeon hif genes were significantly differentially expressed in gills, especially hif-1α and hif-3α, with more than 20-fold changes, suggesting their important roles in adaptation to hypoxia in hybrid sturgeon. A meta-analysis indicated that the HIF pathway, a major pathway for adaptation to hypoxic environments, was activated in the liver of the hybrid sturgeon 24 h after the hypoxia challenge. Our study demonstrated that hypoxia, particularly severe hypoxia (1.00 ± 0.1 mg/L), could cause considerable stress for the hybrid sturgeon. These results shed light on their adaptive mechanisms and potential biomarkers for hypoxia tolerance, aiding in aquaculture and conservation efforts.

To systematically evaluate FB’s effects on tilapia muscle quality, two distinct experimental phases are designed, the crispy texture development phase (0–16 weeks) and the crispy texture retention phase (17–24 weeks), which can determine the minimum faba bean (FB) feeding duration required to achieve optimal textural modification and can assess the persistence of improved textural properties following FB withdrawal, respectively. The results demonstrated that a 60% FB inclusion diet administered for 16 weeks did not adversely affect tilapia growth performance. Significant improvements in textural parameters, including hardness, springiness, chewiness, and shear force, were observed in FB-fed tilapia as early as 8 weeks, with these enhancements being maintained throughout the 16-week feeding period. These superior textural characteristics persisted during the subsequent retention phase following FB withdrawal. Microstructural analysis revealed that the 60% FB diet significantly enhanced muscle-fiber density while reducing fiber diameter in tilapia during the 8–16 week feeding period. These microstructural modifications persisted throughout the texture retention phase, maintaining significant differences compared to the control group. Serological analysis demonstrated the FB group elevated Superoxide dismutase (SOD) activity and reduced malondialdehyde (MDA) levels at 4 weeks, though these differences normalized thereafter. qRT-PCR showed the 60% FB clearly increased the expression of mstn at 8 weeks, while col1a-2 and myog expressions also obviously improved at 12 weeks. In summary, dietary 60% FB improved tilapia muscle crispiness by altering texture and microstructure via gene-expression regulation. The minimum duration was 8 weeks to achieve crispiness in tilapia by the 60% FB diet without adverse effects on growth, immunity, and hepatopancreas function. Furthermore, the crispy texture of tilapia fillets was maintained for at least 2 months following withdrawal of the 60% FB diet after 16 weeks of continuous feeding.

The hybrid sturgeon (HS, Acipenser baerii Brandt ♀ × A. schrenckii Brandt ♂) was compared with its parental varieties (Siberian sturgeon (SS) and Amur sturgeon (AS)) to evaluate muscle quality differences. Three sturgeon species were bred from the same batch, reared under identical conditions until three years of age, and then male fish from each species (AS, 3.2 ± 0.18 kg; SS, 2.5 ± 0.14 kg; HS, 3.5 ± 0.21 kg) were sampled for analysis of muscle nutritional composition, texture, microstructure, and metabolomics. Results showed no significant differences in proximate composition, hydrolyzed amino acids, pH, or water-holding capacity among the three groups. However, HS exhibited higher gumminess and chewiness than both parent species, as well as greater hardness and springiness compared with the SS. Muscle fiber density was higher in HS than in the AS, but no significant difference was observed between HS and SS. Levels of free amino acids (Val, Ile, Ala) were lower in HS than in AS. In terms of fatty acid profiles, HS showed elevated polyunsaturated fatty acids compared with SS, resembling the pattern observed in AS. Muscle color of HS was similar to that of SS, whereas its a* value differed from those of AS. Metabolomics identified differential metabolites (GABA, D-glucosaminic acid, AP4) enriched in pathways such as ABC transporters, protein digestion and absorption, and amino acid metabolism. Overall, HS combines improved texture traits with meat quality attributes resembling SS (muscle color, free amino acids) and AS (polyunsaturated fatty acids). These characteristics suggest that HS possesses a distinctive combination of meat quality traits.

Background: Largemouth bass ranavirus (LMBV) triggers heavy mortality in farmed Largemouth bass (Micropterus salmoides). Oral subunit vaccines are suitable for mass fish immunization yet often yield unsatisfactory immunity. Intestinal microbiota strongly modulates mucosal immune competence. This study assessed whether PLGA/selenium nanoparticle (P/Se) pretreatment enhances protection afforded by a PLGA-based oral subunit vaccine (P/V) against LMBV. Methods: A 2 × 2 factorial design was applied. Fish received 28-day oral P/Se pretreatment followed by three oral doses of P/V. Material characterization, 16S rRNA high-throughput sequencing combined with microbial assembly analysis (diversity, NST, Sloan neutral model), qRT-PCR for immune related genes, serum specific antibody ELISA, LMBV immersion challenge and histopathological examination were conducted. Results: P/Se and P/V microspheres were successfully fabricated with acceptable particle size, and loading efficiency. P/Se pretreatment significantly elevated gut microbial α-diversity and enriched Actinobacteriota, in addition to increasing the relative contribution of stochastic processes to gut community assembly. The combined pretreatment–vaccine group markedly up-regulated intestinal mucosal immune genes (IL-1β, IL-8, IFN-γ, TNF-α, IgT) and systemic IgM. Consistently, higher serum-specific IgM antibody levels, improved survival rate, and alleviated virus-induced pathological injuries in trunk kidney and liver were observed in this combined group. Vaccination alone only conferred limited protection, and pretreatment alone produced no obvious antiviral protection. Conclusions: P/Se sequential intervention remodels intestinal microbiota and enhances the protective potency of oral subunit vaccine. This sequential feeding strategy offers a feasible way to optimize oral-vaccine performance for cultured largemouth bass.