Effects Of Dietary Lipid And Bile Acid Levels On Growth, Body Composition, Digestibility Physiology And Lipid Metabolism Of Juvenile Turbot(Scophthalmus Maximus)

Bile acids are substances produced a series of steroid cholesterol metabolism. Bileacid could improve lipase activity, promote digestion and absorption of lipids; regulatecholesterol homeostasis; bactericidal anti-inflammatory to improve immunity ofanimals and so on. The objective of this study was to investigate the effects of dietarybile acid on lipid utilization capacity of juvenile turbot(Scophthalmus maximus) in twoexperiments. Firstly, the objective of this study was to investigate the effects of dietarybile acids on growth performance,digestion and aquatic environment of juvenile tubot(Scophthalmus maximus)at different dietary lipid levels. Secondly, the objective of thisstudy was to investigate the effects of dietary bile acids with0%and1.5%on growthperformance, body composition and lipid metabolism of juvenile turbot (Scophthalmusmaximus) at two dietary lipid levels(10%and18%).The details are as follows:Abstract1The objective of this study was to investigate the effects of dietarybile acids on growth performance， digestion and aquatic environment of juveniletubot(Scophthalmus maximus) at different dietary lipid levels. The fish with averageweight of(45.78±0.11)g were fed five isonitrogenous diets with different levels(10%,12%,14%,16%and18%) of lipid and1.5%bile acid for8weeks. The results showedthat the weight gain rate(WGR), special growth ratio(SGR)and protein efficiencyratio(PER)increased and then decreased beyond the level of16%, while the feedconversion ratio(FCR) showed a contrary trend. According to the quadratic regressionmodel based on SGR, the optimal dietary lipid level and protein/energy ratio was17.36%and21.54mg/KJ, respectively. The crude lipid contents of whole fish and livershowed a positive correlation with dietary lipid levels. The apparent digestibility of drymatter, crude protein and crude lipid were significantly increased by diets supplemented with bile acids(P<0.05). Contents of serum lipid were increased with the increase ofdietary lipid levels(P<0.05). The activities of AST and ALT in serum were the highestthan other groups at the18%level(P<0.05). Dietary lipid had an significant effect onlipid metabolic enzymes(P<0.05). Lipoprotein lipase(LPL), hepatic lipase(HL), totallipase(HL) and intestinal lipase(LPS) activities increased with the increasing dietarylipid levels. The contents of nitrite, ammonium salt, nitrate and phosphate in aquaticenvironment were higher than other groups at the16%lipid level(P<0.05). Thecumulative mortality was the lowest than other groups at the16%lipid level, while thevibrio anguillarum infection resistance was maximum. Above of all, bile acidsupplementation could significantly improved tolerance of lipid, reduced the optimalprotein/energy ratio. Lipid levels of diets were increased nutrients digestibility. Lipidlevels of diets accelerated lipid metabolism enzymes activities and vibrio anguillaruminfection resistance. Lipid levels of diets were not affect aquaculture quality.Abstract2The objective of this study was to investigate the effects of dietary bile acids on growth performance, body composition and lipid metabolismof juvenile turbot(Scophthalmus maximus) at two dietary lipid levels. The fishwith initial average weight of (45.48±0.21)g were fed four isonitrogenous diets atlevels of10%and18%supplemented with0%and1.5%bile acids for8weeks,respectively. With dietary increasing lipid levels or bile acids supplementation, growth rate, specific growth rate and protein efficiency were significantly increased(P<0.05); however, feed conversion ratio was reduced(P<0.05). Adding bile acids to diets significantly promoted fish growth, while hepatosomatic index was decreased at the same lipid level(P<0.05). Crude lipid contents of tissues showed anincreasing trend as lipid levels increased, while adding bile acids reduced the accumulation of crude lipid contents in tissues. Moisture and crude protein contentsof whole fish and muscle were mainly affected by diets supplemented with bileacids(P<0.05). Adding bile acids to diets significantly effected lipid metabolismin tissue at two different lipid levels, moreover changed fatty acid composition in muscle and liver. Addition of bile acids significantly reduced PUFA content ofmuscle and liver(P<0.05), and increased SFA and MUFA contents. For fish feddiets with10%and18%lipid levels, addition of bile acids significantly reducedcontents of serum triglyceride, total cholesterol, high-density lipoprotein cholester ol, low-density lipoprotein cholesterol, as well as the activities of ALT and AST(P<0.05).However, the serum biochemical indices showed an opposite trend withthe increasing dietary lipid levels. The activities of superoxide dismutase(SOD) and catalase(CAT) in serum of fish fed diets with two lipid levels and bile acidswere significantly increased(P<0.05). The activities of alkaline phosphatase(ALP),acid phosphatase(ACP), Lysozyme(LZM) and total bile acid(TBA) were affectedby diets supplemented with two lipid levels and bile acids(P<0.05), but total bilirubin(TBIL) activity was not significantly effected(P>0.05). In terms of lipid metabolism enzymes, increasing the dietary lipid levels or bile acids supplementationsignificantly elevated activities of lipoprotein lipase, hepatic lipase, TL and intestinal lipase(P<0.05), moreover statistical interaction of dietary lipid and bile acidswas found on activities of lipid metabolism enzymes(P<0.05). The results indicate that adding bile acids to diets can not only promote growth performance andfeed utilization, but also reduce the accumulation of body fat and thereby protectliver functions of juvenile turbot. bile acids were increased antioxidant, non-specific immune indices of juvenile turbot at two dietary lipid levels，accelerated thePUFA absorption and utilization in juvenile turbot.