本试验在以酪蛋白和明胶为蛋白源的纯化日粮（镁含量76.9 mg/kg）中添加不同水平的镁（0、150、300、600、1 200和2 400 mg/kg），研究了镁对草鱼生长和脂肪代谢的影响。选取540尾体重为（10.68±0.14）g的草鱼，随机分入6个处理，每个处理3个重复，每个重复30尾鱼。进行为期10周的生长试验。结果表明：1）日粮中添加适量镁显著提高草鱼的特定生长率、增重率和饲料效率（P<0.05），当饲料镁含量为692.0 mg/kg时，以上3项指标均达到最大值；2）日粮中添加适量镁能增加草鱼体脂沉积率、血脂水平、肝胰脏脂肪酶和苹果酸脱氢酶活性（P<0.05），降低肝胰脏脂蛋白酯酶活性（P<0.05），但对肠道脂肪酶活性没有显著影响（P>0.05）。由此可知，日粮中适当添加镁能显著促进草鱼生长，添加量为600 mg/kg（日粮镁含量692.0 mg/kg）时效果最好；镁能够增强草鱼肝胰脏的脂肪合成能力，降低其脂肪转运能力；镁使肝脂蛋白酯酶活性降低，导致高血脂。

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) (P<0.05), 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 (P<0.05). However, the lipase activity in intestine showed no significant differences among the groups (P<0.05). 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.［Chinese Journal of Animal Nutrition, 2010，22（1）:93-99］