Optimum feeding frequency of juvenile largemouth bass (Micropterus salmoides) reared in in-pond raceway recirculating culture system

Abstract

This study was conducted to determine the effects of feeding frequency on the growth, serum biochemical parameters, antioxidant status and hepatic growth hormone (GH), insulin-like growth factor I (IGF-I), lipoprotein lipase (LPL) and hepatic lipase (HL) gene expression levels of juvenile largemouth bass (Micropterus salmoides) reared in an in-pond raceway recirculating culture system (IPRS). Fish (initial body weight 5.0 ± 0.4g) were hand-fed with a commercial diet under one of three different feeding frequency treatments (2, 3 or 4 meals/day) for 120days. The results indicated that no significant differences were observed in the final body weight, weight gain and specific growth rate of fish fed different feeding frequencies on 30days and 60days (P > 0.05). Fish fed 2 times/day had higher growth than that fed 4 times/day on 90days but had higher growth than those fed 3 and 4 times/day on 120days. No significant differences were found in serum alanine aminotransferase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP) activities, total protein (TP), lysozyme and triglyceride (TG) content, hepatic total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-PX) activities and malondialdehyde (MDA) content among fish fed different feeding frequency (P > 0.05). Serum glucose (Glu) content and catalase (CAT) activity decreased, while total cholesterol (TC) content increased with increasing feeding frequency. Fish fed 2 times/day had higher hepatic total superoxide dismutase (T-SOD) than that fed 4 times/day on 60days, 90days and 120days (P < 0.05). Fish fed 2 times/day had higher IGF-1 gene mRNA expression on 30days, 60days and 120days (P < 0.05), while no significant difference on 90days. No significant difference was found in GH gene mRNA expression on 30days and 60days, while fish fed 4 times/day had lower values than that fed 2 times/day on 90days and 120days (P < 0.05). Fish fed 2 times/day had significantly higher LPL mRNA expression level than that fed 4 times/day on 60days and 90days and had significantly higher HL mRNA expression level on 60days, 90days and 120days (P < 0.05). Based on growth, physiology, hepatic gene expression levels, labour costs and intensity, the optimal feeding frequency of largemouth bass (average body weight 5.0 ± 0.4g) reared in IPRS is 2 times/day. These data are very necessary for the optimizing of culture conditions and feeding management strategy in IPRS culture operations.