Effects of Dietary Lipid Levels on the Lipid Deposition and Metabolism of Subadult Triploid Rainbow Trout (Oncorhynchus mykiss)

Abstract

A growth trial was conducted to evaluate the effects of dietary lipid levels on the lipid deposition and metabolism of subadult triploid rainbow trout. Diets with low (148 g lipid kg-1 diet), moderate (228 g lipid kg-1 diet), and high (294 g lipid kg-1 diet) crude lipid contents were fed to quadruplicated groups of fish ( $233\text{g}\pm 0.2\text{g}$ ) for 80 days, and they were named as LL, ML, and HL, respectively. Results showed that the lowest and highest values of condition factor and hepatosomatic index were shown in the LL group, respectively, while the HL group obtained the highest liver redness value, plasma total cholesterol, high-density lipoprotein-cholesterol, and low-density lipoprotein-cholesterol contents ( $P<0.05$ ). The viscerosomatic index and plasm glucose, nonesterified fatty acids, and triglyceride contents were comparable among groups ( $P>0.05$ ). As for lipid deposition, viscera and muscle were the main lipid storage place for triploid rainbow trout when tissues’ weight is taken into consideration. Overall quantitative PCR showed that the lipid uptake, triglyceride, and fatty acid catabolism were upregulated, but glycolysis was downregulated as dietary lipid increased. The expression of genes involved in lipogenesis, lipoprotein clearance, very low-density lipoprotein assembly, and glycogenesis was not affected by dietary lipid levels ( $P>0.05$ ). In summary, subadult triploid rainbow trout store lipid mainly in viscera and muscle; it could maintain hepatic lipid homeostasis when fed with dietary lipid levels ranging from 150 to 300 g kg-1 by regulating lipid uptake and switching energy supply between glycolysis and fatty acids β-oxidation.