Effects of Constant and Diel Cyclic Temperatures on The Liver and Intestinal Phospholipid Fatty Acid Composition in Rainbow Trout Oncorhynchus Mykiss During Seawater Acclimation
Abstract Background: Rainbow trout is an important economic fish in aquaculture and a model species in environmental physiology. Despite of earlier research on the seawater adaptability of rainbow trout at different temperature regimes, the influence on liver and intestine in this species is still unknown. Two trials were conducted to investigate the effects of constant and diel cyclic temperatures on phospholipid fatty acid (PLFA) composition in the liver and intestine of rainbow trout during seawater acclimation.Results: At the end of the growth trial 1, fish at 9 and 12.5°C showed significantly higher ratios of unsaturated to saturated (U/S) and unsaturation index (UI) than those at 16°C in liver and intestine phospholipids. After day 1 of seawater acclimation, the U/S, UI, and average chain length (ACL) of liver and intestine phospholipids in fish at 16°C significantly increased. Two weeks after seawater acclimation, liver and intestinal PLFA composition adapted to salinity change. In trial 2, significantly higher U/S, UI, and ACL were found in intestinal phospholipids at 13±2°C. On the first day after seawater acclimation, UI and ACL in liver phospholipids significantly increased in 13°C, while fish in 13±2°C showed significantly decreased U/S, UI, and ACL in the intestine. At the end of the growth trial 2, liver PLFA compositions were stable, whereas intestinal PLFA in 13 and 13±1°C showed significantly decreased U/S, UI, and ACL. A two-way analysis of variance and principal component analysis revealed significant effects of different constant temperatures, seawater acclimation, and their interaction on the liver and intestinal phospholipids, a significant effect of diel cyclic temperature on intestinal phospholipids, and the effects of seawater acclimation and its interaction with diel cyclic temperature on liver phospholipids.Conclusion: Temperatures of 9 and 12.5°C could elevate membrane fluidity and thickness in the liver and intestine of rainbow trout in freshwater, whereas no significant effects were found with diel temperature variations. After seawater acclimation, constant and diel cyclic temperatures significantly influenced the liver and intestine's membrane fluidity and thickness. Compared with constant temperature, diel temperature variation (13±2°C) can enhance the adaptability of rainbow trout during seawater acclimation.