Integration of transcriptomics and metabolomics reveals the effects of sea currents on overwintering of large yellow croaker Larimichthys crocea in cage culture

Large yellow croaker cultured in cages often face overwintering challenges, which have led to significant economic losses in aquaculture. In natural sea areas, apart from low temperatures, sea current is an important factor affecting the overwintering of large yellow croaker. Therefore, we have set up cages with different mesh sizes to investigate the impact of sea currents on the overwintering of large yellow croaker. Three cages with different mesh sizes (0.5 cm, 1.0 cm, and 2.0 cm) were constructed, and 500 fish were placed in each cage. The group with the 0.5-cm mesh served as the control, while the other two groups were experimental (T1 and T2). Water temperature was monitored daily, and water flow rate was measured at the highest tide point of each month (The first and fifteenth days of the lunar calendar). The experiment lasted for 78 days, during which the body weights and lengths of the fish were measured. Muscle samples were taken for body composition analysis, and liver tissues from control and T2 were collected for transcriptome and metabolome analyses. The water temperature ranged from 8.5 to 12.5 degrees C during the experimental period. The average sea current velocities in the three groups were 0.049 m/s, 0.167 m/s, and 0.286 m/s, respectively. The survival rates of fish in the control, T1 and T2 groups were 85.25%, 80.66%, and 70.32%, respectively. The weight and condition factor decreased significantly in all groups, with the T2 group experiencing the greatest decline. The lipid and protein contents of the fish in the T2 group were significantly lower than those in the control and T1 groups. Transcriptome analysis showed that the insulin and FoxO pathways were related to the regulation of glycolysis/gluconeogenesis. The PPAR signaling pathway was related to the regulation of lipid metabolism. Metabolome analysis revealed 663 significantly different metabolites in the two groups, of which 10 were significantly downregulated and 51 were significantly upregulated. The combined analysis of transcriptome and metabolome showed that both metabolites and genes involved in the ABC transporter pathway were significantly differentially expressed. The results of the study indicated that fish in high flow rate cages require more fat and protein to provide energy. The insulin and PPAR pathways played important roles in regulating glucose and lipid metabolism. The ABC transporter pathway may play important roles in the transport of small molecule substances and participate in energy metabolism during low-temperature activity in large yellow croaker.