Effects of magnesium on growth and lipid metabolism of grass carp (Ctenopharyngodon idellus).

This research was conducted to study the effects of dietary magnesium levels on growth and lipid metabolism of grass carp(Ctenopharyngodon idellus).Purified casein-gelatin-based diets(magnesium content 76.9 mg/kg) supplemented with six levels of magnesium(0,150,300,600,1 200 and 2 400 mg/kg,respectively) were fed to juvenile grass carp with an initial body weight of(10.68±0.14) g for 10 weeks.Five hundred and forty juvenile grass carp were randomly divided into six groups which each had three replicates(thirty fish for each replicate).The results showed that: 1) the optimal dietary level of magnesium increased significantly specific growth rate(SGR),weight gain(WG) and feed efficiency(FE)(P0.05),and the highest were observed in fish fed the diet containing 692.0 mg/kg magnesium;2) the optimal dietary level of magnesium significantly increased the body fat,serum lipid level and activities of lipase and malic dehydrogenase(MDH) in hepatopancreas,and decreased the activities of lipoprotein lipase(LPL) in hepatopancreas of grass carp(P0.05).However,the lipase activity in intestine showed no significant differences among the groups(P0.05).Based on these observations above,the optimal dietary level of magnesium increased significantly growth of grass carp,and the dietary supplementation of 600 mg/kg magnesium that per kg of diet contained 692.0 mg magnesium could gain the best effects.Magnesium could enhance the capacity of lipid synthesis,but reduce lipid transport capacity of hepatopancreas of grass carp.Magnesium could reduce the activity of LPL in hepatopancreas of grass carp and cause hyperlipidemia.