| Vitamin-free casein, gelatin and white fish meal were used as protein sources, fish oil and corn oil(1:1) as lipid sources and corn starch as carbohydrate source, six diets were prepared by supplementing 0, 680, 1361, 2041, 2721 and 4082 mg kg-1 choline chloride, which providing graded levels of choline at 8.1(control group), 602.5, 1 119.0, 1 511.5, 1 970.0 and 4 029.0 mg choline kg-1 diet, respectively. This experiment was consist of six experimental groups with each of three replicates, and each tanks was stocked with 30 fish(juvenile size) or 20 fish(medium size). Fish were hand-fed to apparent satiation twice daily(08:00 and 16:30 h). The feeding trials were conducted in indoor aquarium system(1000L/tank) for 8 or 10-week to investigate the growth and nutritional physiology of choline for grouper(Epinephelus coioides) at two different growth stages. Results are presented as follows:1. Juvenile stage: Survival rate(SR) of juvenile grouper was significantly affected by the levels of dietary choline(P<0.05), which fed the 1 511.5 mg choline kg-1 diet was significantly higher than that of group fed the 1 970.0 mg choline kg-1 diet(P<0.05). Weight gain rate(WGR) and specific growth rate(SGR) were tended to increase firstly and then decrease with dietary choline supplementation(P<0.05), and tendency of firstly decreased and then increased was found in feed conversion rate(FCR)(P<0.05) in the trial, no significant difference of protein efficiency ratio(PER) was found in response to the dietary increasing levels of choline among treatments(P>0.05). On the basis of WGR, the optimum dietary choline requirement of juvenile grouper was estimated using broken-line regression analysis to be 1 562.82 mg choline kg-1 diet. Tendency of firstly decreased and increased was found in juvenile grouper’s hepatosomatic index(HSI) and viscerosomatic index(VSI)(P<0.05), and the minimum values were reached at 1 511.5 mg choline kg-1 group, condition factor(CF) in juvenile phase was decreased gradually and then stable(P<0.05). No significant differences were observed in the whole-body composition of juvenile grouper with increased dietary choline levels(P>0.05). With increasing dietary choline levels, in the juvenile grouper experiment, liver and muscle lipid content were tended to gradually decrease and then stable, liver lipid content of choline added groups significantly lower than that of control(P<0.05), no significant difference was observed among choline added treatments in liver lipid content(P<0.05).Liver choline content in juvenile grouper was increased from 8.1 to 1 119.8 mg choline kg-1 diet, but decreased from 1 119.8 to 1 970.0 mg choline kg-1 diet(P<0.05), and increased again. Based on liver choline concentration, the dietary choline requirement of juvenile grouper was estimated as 1 087.35 mg kg-1 diet. Serum alanine transaminase(ALT), aspartate aminotransferase(AST) and alkaline phosphatase(ALP) were tended to decreased firstly and then increased in juvenile phase by the increment of dietary choline levels(P<0.05), the maximum ALT was reached at the control, minimum AST and ALP were found in 1 511.5 mg choline kg-1 group. Triglyceride(TG) and total cholesterol(TCHO) in serum were significantly increased by 1 511.5 mg choline kg-1 diet group in juvenile grouper(P<0.05), serum high density lipoprotein cholesterol(HDL-C) was tended to increased firstly and then decreased, and a maximum value was appeared in 1 511.5 mg choline kg-1 diet group, which significantly higher than that of control(P<0.05). Enzyme activities of lipid metabolism in juvenile phase were significantly affected by the dietary protein levels. Lipoprotein lipase(LPL) and total lipase(TL) were significantly increased from 602.5 to 1 511.5 mg choline kg-1 diet group(P<0.05), which were highest in 1 511.5 mg choline kg-1 diet group. Hepatic lipase(HL) in the control was evidently lower than other treatments(P<0.05). fatty acid synthase(FAS) activity in 602.5 mg choline kg-1 diet group was significantly lower than other treatments(P<0.05). In juvenile grouper, carnitine acyl-transferase(CACT) activity was gradually decreased with increased dietary choline levels(P>0.05), acetyl-coa carboxylase(ACC) activity were significantly increased in 1 119.8 mg choline kg-1 diet group(P<0.05), and no significant difference were observed among other treatments(P>0.05). In juvenile phase, the expression of liver HL m RNA was significantly lower in 8.1 and 602.5 mg choline kg-1 diet group(P<0.05), but gradually increased with increased dietary choline levels(P<0.05), FAS m RNA expression was significantly higher other treatments in 1 511.5 mg choline kg-1 diet group(P<0.05).2. Medium stage: The tendency of increased and then leveled off was found in the medium stage, SR in the basal diet was significantly lower than fish fed other treatment(P<0.05). WGR, SGR and PER were all tended to increase firstly and then decrease with dietary choline supplementation(P<0.05), and the maximum values were reached at 1 119.0 mg choline kg-1 group, tendency of firstly decreased and increased was observed in feed conversion rate(FCR)(P<0.05). Based on WGR, broken-line regression analysis showed that the optimum dietary choline levels was 986.54 mg choline kg-1 diet. HIS, VSI and CF in medium stage were decreased gradually and then stable with increased dietary choline levels(P>0.05). Moisture and CP in medium phase were not different among treatments(P>0.05), but ether extract(EE) and ash had maximal value in 1 119.0 mg choline kg-1 group and 4 029.0 mg choline kg-1 group, respectively(P<0.05). Decreased firstly and then increased disappeared in lipid content of liver in medium grouper, but an opposite trend was showed in muscle lipid content(P<0.05). Liver choline concentration reached a plateau in 1 511.5 mg choline kg-1 diet and then leveled off(P<0.05). Broken-line regression of liver choline content indicated that choline requirement of medium grouper was 1 579.68 mg kg-1 diet. The maximum AST and ALP was found in control, ALT was tended to decreased firstly and then increased by the increment of dietary choline levels(P<0.05). Serum TG had a maximum value in 1 511.5 mg choline kg-1 diet group, which significantly higher than that of control(P<0.05), TCHO and HDL-C were increased firstly and then decreased with increasing dietary choline levels in medium stage(P<0.05). In the medium grouper experiment, LPL and TL were significantly increased(P<0.05), HL was not affected by the dietary choline levels(P>0.05). FAS activity, in medium grouper, was gradually decreased and then stabilized(P<0.05), maximum CACT activity was found in 1 119.8 mg choline kg-1 diet group(P<0.05), which evidently higher than that of control, ACC activities in liver was no affected by the dietary choline levels(P>0.05). HL and FAS m RNA in medium grouper had maximum expression levels in 1970.0 and 1 119.0 mg choline kg-1 diet group(P<0.05), and tended to gradually increased and increase firstly and then decrease, respectively. |
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