Dietary conjugated linoleic acid (CLA) and lecithin affects levels of serum cholesterol, triglyceride, lipoprotein and hypoxic stress resistance in rainbow trout (Oncorhynchus mykiss)

Considering the role of conjugated linoleic acid (CLA) and soybean lecithin (SBL) in fat digestion, absorption and metabolism as well as stress resistance in aquatic organisms, the current study was a 74-day attempt to investigate the synergistic effects of these two compounds on stress resistance and blood lipoprotein levels of rainbow trout (Oncorhynchus mykiss) weighing 120±5 g. Nine isonitrogenous and isocaloric experimental diets containing 1, 2 and 3% CLA and 2, 3 and 4% soybean lecithin on the basis of the basal control diet (free from CLA and lecithin) were formulated. The fish were exposed to three ascending periods of hypoxic stress (7.5, 15 and 30 min) at the end of culture period. The dissolved oxygen was decreased to 1.96 ppm by injecting nitrogen gas. Significantly higher levels of cortisol and glucose were detected in fish fed on diets having higher levels of SBL (2%) and CLA (3%) at higher stress time improving the resistance to hypoxia stress (P≤0.05). Moreover, levels of triglyceride (TRG), cholesterol (COL), low density lipoprotein (LDL), very low-density lipoprotein (VLDL) and high density lipoprotein (HDL) also increased significantly compared to the control group (P≤0.05). This study reveals that using 2% SBL and 3% CLA in rainbow trout feed can promote resistance to hypoxic stress.