Abstract
A feeding experiment was conducted to determine the substitutional effects of dietary methionine (Met), choline (Ch), betaine (Bet) and soy beau lecithen (Lec) on lipid accumulation in liver of grass carp, Ctenopharyngodon idellus (C. et V.), weighing about 15g, which were fed separatedly 11 diets containing different levels of these four substances. The dietary levels of these sunbstances were (%): (1) 1.1Met 0.08Ch, (2) 1.1Met 0.33Ch, (3) 1.3Met 0.23Ch, (4) 1.5Met 0.13Ch,(5) 1.3Met 0.13Ch, (6) 1.3Met 0.13Ch 0.08Bet (7) 1.3Met 0.13Ch 0.1Bet (8)1.3Met 0.13Ch 0.12Bet (9) 1.3Met 0.13Ch 4.0Lec, (10) 1.3Met 0.13Ch 6.0Lec and (11) 1.3Met 0.13Ch 8.0Lec. After a 52-day feeding period, the diet supplemented with 1.1% methionine and 0.08% choline resulted in the lowest growth rate and the highest liver lipid content and the addition of different levels of choline, betaine or soy beau lecithin to the diets increased the relative growth rate by 17- 73% and decreased the liver lipid content by 26-74%. Some significant differences in the liver lipid content were observed among the groups of fish fed different diets, showing a coordinated action and a substitional relationship among these four substances. When analyzing the lipid content of serum and liver as well as the serum lipoprotein components, it was found that the lipid content in serum increased with the decrease of that in liver, the coefficient of correlation (r) being - 0.7804, and the same was true for the level of serum pre-β plus β-lipoproteins (r = - 0.6897). So, it may be deduced that the decreased accumulation of lipids in grass carp liver by dietary methionine, choline, betaine and soy beau lecithin was accomplished, to some extent,by increasing the biosynthesis of serum lipoproteins responsible for the transport of lipids from liver to extra-hepatic tissues.
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