Effects of Different Marine-Based Lipid Sources on Growth Performance, Activities of Digestive Enzyme, Antioxidant Responses, and Lipid Metabolism of Large Yellow Croaker (Larimichthys crocea) Larvae

Abstract

The study of lipid nutrition is an important guarantee for the development of high-efficiency artificial microdiet for fish larvae. Existing studies on lipid nutrition of larvae mainly focus on nutrient requirements and metabolism through a single lipid source. However, there are few reports on the effects of different marine-based lipid sources on fish larvae. In this study, a 30-day feeding experiment was conducted to evaluate the effects of different dietary marine-based lipid sources on survival, growth performance, appetite gene expression, activities of digestive enzyme, antioxidant responses, and lipid metabolism of large yellow croaker (Larimichthys crocea) larvae (initial weight $4.71\pm 0.21\text{mg}$ ). Four isonitrogenous (520 g/kg crude protein) and isolipidic (190 g/kg crude lipid) diets were formulated to contain fish oil (FO), krill oil (KO), squid viscera oil (SVO), and Schizochytrium sp. oil (SSO), respectively. Results showed that larvae fed with the SSO diet had significantly higher survival rate (SR) than those fed with dietary FO and SVO ( $P<0.05$ ). However, larvae fed with the SSO diet had significantly lower final body weight (FBW) and specific growth rate (SGR) than those fed with other diets ( $P<0.05$ ). Furthermore, larvae fed with the SSO diet had significantly higher percentage of total n-3 long-chain polyunsaturated fatty acids (LC-PUFA) than those fed with other diets, followed by KO and SVO diets ( $P<0.05$ ). Larvae fed with the SSO diet had significantly lower mRNA expression of orexigenic genes (npy and ghrelin) and significantly higher mRNA expression of anorexigenic gene (cart) than those fed with dietary FO ( $P<0.05$ ). Meanwhile, larvae fed with the SSO diet had significantly higher activity of alkaline phosphatase (AKP) in intestinal segments (IS) and brush border membrane (BBM) than those fed with dietary FO and SVO ( $P<0.05$ ). Larvae fed with the SSO diet had significantly higher activity of total antioxidant capacity (T-AOC) than those fed with dietary FO ( $P<0.05$ ). The TG content and mRNA expression of lipogenesis genes (srebp-1c, fas, and scd1) were markedly lower in larvae fed with SSO, KO, and SVO diets than in those fed with dietary FO ( $P<0.05$ ). Meanwhile, larvae fed with KO and SSO diets had significantly higher mRNA expression of the lipolysis gene (cpt-1) than those fed with other diets ( $P<0.05$ ). In conclusion, results of the present study showed that FO can be completely replaced in large yellow croaker larvae feed with KO and SVO without negative effects. Moreover, the complete replacement of FO by SSO can improve survival, activities of digestive enzyme, antioxidant responses, and lipid metabolism, despite inhibiting the appetite and growth of large yellow croaker larvae.