| Popis: |
Rearing density is a critical factor for both the productivity and welfare of farmed fish. The present study examined juvenile black sea bream (Acanthopagrus schlegelii) at low (LD), standard (control, CR), moderately high (MD), and high (HD) densities over a 60-day period. The effects of density on physiological aspects of growth, survival, stress response (cortisol), osmosis and ion balance (Na+–K+–ATPase and Ca2+–Mg2+–ATPase), energy metabolism (glucose, lactic acid, and lactic dehydrogenase), digestive enzyme activity (lipase, trypsin, and amylase), antioxidant ability (superoxide dismutase and malondialdehyde), and non-specific immunity (lysozyme) were investigated to evaluate potential physiological improvements in this commercially and ecologically important species under different densities. Both transcriptomic and metabolomics approaches were applied to assess metabolic and transcriptional changes among groups to determine the underlying mechanisms of physiological performance. The results showed that juveniles reared under low density had not only significantly improved growth and survival rate but also significantly reduced energy expense and lower activities of digestive and antioxidant enzymes compared with fish reared under high density. Significantly reduced cortisol and malondialdehyde contents in the LD group indicated less stressful conditions in those fish. Transcriptomic analysis showed that differentially expressed genes (DEGs) were involved in pancreatic secretion, protein digestion and absorption, and protein processing in the endoplasmic reticulum pathway. Metabolomics revealed that significantly different metabolites (SDM) were involved in the biosynthesis of amino acids, ABC transporters, 2-oxocarboxylic acid metabolism, and protein digestion and absorption. A combined analysis of transcriptome and metabolome showed that fish in the LD group exhibited reductions in energy expenditure, osmotic regulation, and antioxidant ability, while fish in the HD group showed higher energy expenditure, digestive ability, and immune regulation. These findings have important implications for the improvement of fish growth and welfare as well as in mechanistic studies of rearing density. |
