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.

Wnt genes encode a family of secretory glycoproteins that are involved in various stages of organ development through regulation of cell proliferation, differentiation, and growth. Recently, Wnt genes have been shown to play an important role in regeneration processes. However, there have been no previous genome-wide analyses of the Wnt gene family members in crab species. In this study, a total of 13 Wnt family genes were identified from the genome of the swimming crab Portunus trituberculatus and classified into three main groups based on the conserved domain, protein sequence, and motifs. Chromosome location analysis showed that tandem duplication may have resulted in the expansion of the PtWnt gene family. RNA-seq results indicated that most PtWnt genes had a higher Fragments Per Kilobase of transcript sequences per Million base pairs (FPKM) value in the regenerating limb bud muscle than in the normal limb muscle, and the genes were enriched in a number of pathways that had biological functions underlying limb regeneration such as the cell surface receptor signaling pathway, the hippo signaling pathway, receptor binding, and basal cell carcinoma. Moreover, quantitative real-time PCR (RT-qPCR) analysis confirmed that the expression levels of nine PtWnts except for PtWnt1, PtWnt2, and PtWnt6 had a consistently increasing trend during limb regeneration. PtWnt1, PtWnt2, and PtWnt6 exhibited significantly up- or down-regulated expression at different limb regeneration stages. These results provide valuable information for further evolutionary and functional characterization of PtWnt genes and indicate the complexity and specialized mechanism of the Wnt signaling pathway regulating regeneration in crustaceans.

Overwintering is an important part of the life cycle of Scylla paramamosain. Salinity has a significant effect on the growth and metabolism of overwintering S. paramamosain. 4‰ and 25‰ are typical salinities in different regions where S. paramamosain overwinters. In order to find the optimum salinity for overwintering, the metabolites in overwintering S. paramamosain at salinities of 4‰ and 25‰ were analysed and compared using GC–MS technology. In this study, the weight gain rate of S. paramamosain was 5.51% at 4‰ salinity and 10.69% at 25‰ salinity after overwintering. A total of 1254 valid peaks and 373 metabolites were detected, including 160 significantly different metabolites (16 down‐regulated metabolites and 144 up‐regulated metabolites). In the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, 22 pathways were associated with metabolic changes; they have or identified L‐isoleucine, L‐lysine, urea, D‐ribose‐5‐phosphate, glucose‐6‐phosphate, fumaric acid, L‐lactic acid, docosahexaenoic acid and palmitic acid. Compared with the 25‰ salinity group, 4‰ salinity group promoted amino acid metabolism, carbohydrate metabolism, membrane transport and lipid metabolism through these differential metabolites, so that overwintering S. paramamosain needs to participate in more metabolic activities at 4‰ salinity, and hepatopancreas consumes more energy to maintain life activities, which indicated that 4‰ salinity was not conducive to the overwintering of S. paramamosain.

Background: Anxiety refers to the pathological persistence and intensification of emotional responses to danger, affecting health from psychological and physical aspects. Serotonin is an important neurotransmitter involved in the onset of anxiety. Methods and Results: To explore the biological changes in the formation of anxiety in crustaceans under the regulation of serotonin, we applied the open field-like test method for assessing anxiety states of larval Portunus trituberculatus, a highly aggressive crustacean species with a more simple neural structure compared with rodents and mammals. Compared with the control group, serotonin treatment resulted in a significant decrease in the time spent by the larvae in the central zone, suggesting anxiety-like behavior. Clonazepam treatment reversed this result and provided further evidence that the behavior of larval P. trituberculatus displayed anxiety. Moreover, a non-targeted metabolomic analysis found a significant alteration in the metabolites involved in tryptophan metabolism pathways associated with anxiety, including L-kynurenine, N-acetyl serotonin, and serotonin. These metabolites are involved in the serotonin pathway, the kynurenine pathway, and other pathways that affect anxiety through tryptophan metabolism. There were no significant differences in tryptophan metabolism levels between the control and clonazepam treatment groups. Conclusions: Our results demonstrate the possible existence of anxiety-like behavior in the larvae of P. trituberculatus from two perspectives. Being a species with a simpler neural structure than that of mammals, the larvae of P. trituberculatus offer a convenient model for studying the mechanisms of anxiety in crustaceans.