Effects of dietary soybean lecithin on growth performances, body composition, serum biochemical parameters, digestive and metabolic abilities in largemouth bass Micropterus salmoides

Abstract

We conducted an 8-week feeding trial to explore the effects of dietary soybean lecithin (SBL) on growth performance and metabolic abilities in juvenile largemouth bass Micropterus salmoides. The addition of 4 % SBL to the feed significantly increases the specific growth rate (SGR), carcass ratio (CR) and crude protein in the fish body and muscle compared with control groups (0 %) (P < 0.05). However, 4 % SBL significant declines contents of total glucose, total bile acids and blood urea nitrogen and activities of ALT and AST in the serum compared with controls (P < 0.05). And 4 % SBL markedly increased contents of serum hormones involved in metabolism and food intake including adiponectin, agouti-related peptide, apelin and insulin (P < 0.05), while decreased cholecystokinin contents compared with controls (P < 0.05). Lipase and amylase activities in the liver and intestine were both significantly increased in 4 % and 8 % SBL groups (P < 0.05). 4 % and 8 % SBL could heighten the enzyme’s activities and genes’ mRNA levels involved in glycolysis (GCK, PFK, PK, MDH) and glycogen synthase (GS) compared with controls (P < 0.05). Meanwhile, contents of AC-CoA and glycogen in the fish liver were also significantly increased in 4 % and 8 % SBL groups compared with controls (P < 0.05). However, the activities and mRNA levels of G6P and PEPCK were not influenced in the liver of tested fish fed with 4 % SBL compared with controls (P > 0.05). In addition, 4 % SBL elevated activities and mRNA levels of FAS in the fish liver compared with controls (P < 0.05). Similarly, 4 % SBL increased the transcriptional levels of genes involved in triglycerides (TG) synthesis (GK, GPAT3 and DGAT2) and lipid transport (FATP1, CD36, APOB100 and FABP10) in the fish liver compared with controls (P < 0.05). Moreover, the mRNA expression levels of up-stream regulatory elements involved in metabolic signal processing (AKT1, mTOR, SREBP1 and PPARγ) were also markedly heightened in fish fed 4 % SBL compared with controls (P < 0.05). Together with these results, it indicated 4 % dietary SBL could increase growth and digestive abilities, improve serum biochemical indicators and hormones, promote glycolysis and glycogen synthesis, and facilitate lipid synthesis and transport in juvenile largemouth bass Micropterus salmoides.