Histology, physiology, and glucose and lipid metabolism of Lateolabrax maculatus under low temperature stress

Spotted sea bass (Lateolabrax maculatus) is a popular and important commercial fish throughout the world, but it is unknown whether introducing domesticated fish to locations that experience cold weather might alter physiological performance. In this study, we evaluated the behavior, fatty acid content, histological analysis of liver and gills, liver enzymatic activity in carbohydrate and lipid metabolism, and gene expression in liver related to carbohydrate and lipid metabolism of spotted sea bass acclimatized at 22 °C (control), 16 °C, 10 °C, 8 °C, and 4 °C for 24 h, and 8 °C for 4 days. When L. maculatus was exposed to acute cold stress for 24 h, the gill showed curling, lamellar disorganization, lamellar epithelium hyperplasia, and formed aneurysms inside of the secondary lamellae. Long term stress over four days resulted in severe lamellar epithelium hyperplasia and curling. Continued extreme cold exposure (4 °C) in L. maculatus caused liver HK, PK levels and LDH activities to achieve a peak value at 0 h, and decreased over time. These indicated that glucose metabolism might play critical roles in the initial time of stress. Results of carbohydrate and lipid metabolism showed that lipids appear to play roles in prolonged cold stress. The constitutive transcriptional levels of six genes related to glucose (G6Pase) and lipid metabolism (PPAR-α, PPAR-γ) and mTOR signal pathway (eif4ebp1, eif4ebp2, mlst8) genes increased significantly in most groups during cold stress.