It is of great significance for the aquaculture industry to determine how rearing salinity impacts fish flesh quality. In the present study, largemouth bass was cultured in different salinities (0%, 0.3%, 0.9%) for 10 weeks, and the effect on flesh texture, flavor compounds, taste, and fatty acid composition was evaluated. We show that rearing salinity not only increased flesh water-holding capacity, but also enhanced muscle hardness, chewiness, gumminess, and adhesiveness, which was consistent with the finding in the shear value test. Morphology analysis further revealed that the effect of salinity on flesh texture was probably related to changes in myofibril diameter and density. As for the taste of the flesh, water salinity improved the contents of both sweet and umami amino acids, and reduced the contents of bitter amino acid. Meanwhile, the content of IMP, the dominant flavor nucleotide in largemouth bass muscle, was significantly higher in the 0.9% group. Interestingly, electronic-tongue analysis demonstrated that the positive effect of salinity on flavor compounds enhanced the umami taste and taste richness of flesh. Moreover, rearing salinity improved the contents of C20: 5n-3 (EPA) and C22: 6n-3 (DHA) in back muscle. Therefore, rearing largemouth bass in adequate salinity may be a practical approach to improving flesh quality.

The fatty acid compositions of the fish muscle and liver are substantially affected by rearing environment. However, the mechanisms underlying this effect have not been thoroughly described. In this study, we investigated the effects of different culture patterns, i.e., marine cage culture and freshwater pond culture, on long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis in an aquaculturally important fish, the Japanese sea bass (Lateolabrax japonicus). Fish were obtained from two commercial farms in the Guangdong province, one of which raises Japanese sea bass in freshwater, while the other cultures sea bass in marine cages. Fish were fed the same commercial diet. We found that omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) levels in the livers and muscles of the marine cage cultured fish were significantly higher than those in the livers and muscles of the freshwater pond cultured fish. Quantitative real-time PCRs indicated that fatty acid desaturase 2 (FADS2) transcript abundance was significantly lower in the livers of the marine cage reared fish as compared to the freshwater pond reared fish, but that fatty acid elongase 5 (Elovl5) transcript abundance was significantly higher. Consistent with this, two of the 28 CpG loci in the FADS2 promoter region were heavily methylated in the marine cage cultured fish, but were only slightly methylated in freshwater pond cultured fish (n = 5 per group). Although the Elovl5 promoter was less methylated in the marine cage reared fish as compared to the freshwater pond reared fish, this difference was not significant. Thus, our results might indicate that Elovl5, not FADS2, plays an important role in the enhancing LC-PUFA synthesis in marine cage cultures.

This study aimed to evaluate the effects of solid-state fermented commercial pelleted feed with Lactobacillus plantarum on growth performance, digestive physiology, antioxidant, and immune capacity, as well as morphology and microbiota in intestinal of Tachysurus fulvidraco. A total of 420 fish (49.96 ± 7.10 g) were randomly allocated to twelve 300 L buckets for a 60 d farming trial. The diets of three treatments were established: the untreated commercial diet (UCD), the commercial diet mixed with fermented liquid (MFLD), and the solid-state fermented commercial diet (SSFD). The results indicated that SSFD treatment had a significant positive effect on the growth performance of T. fulvidraco, with an increase of 15.69% to 16.57% (p < 0.05) compared with UCD and MFLD treatments. MFLD and SSFD treatments also showed higher total anti-oxygen capacity, catalase, and glutathione peroxidase activities in the intestine significantly compared with UCD treatment (p < 0.05). Furthermore, the activities of alkaline phosphatase and lysozyme activities both in the liver and intestine were significantly higher in MFLD and SSFD treatments than in UCD treatment (p < 0.05). The villus height in the midintestine was also greater in MFLD and SSFD treatments compared with UCD treatment (p < 0.05). Regarding the intestinal microbiota, the dominant bacteria in UCD treatment was Cetobacterium, with the highest abundance in whole intestinal segments. However, in MFLD and SSFD treatments, the abundance of Cetobacterium in the foreintestine significantly decreased (p < 0.05). In conclusion, this study elucidates that solid-state fermentation feed may not only improve the digestive capacity, antioxidant ability, immune function, and intestinal morphology of T. fulvidraco to enhance growth performance but also influence intestinal microbial composition. These findings provide beneficial proof for developing fermented feed of T. fulvidraco.