The Effect Of High Levels Of Dietary Starch On Growth, Metabolism And Body Composition For Gibel Carp(Carassius Auratus Gibelio)

The present study is to investigate the effect of high levels of dietary starch on growth,metabolism and body composition for omnivorous gibel carp(Carassius auratus gibelio),which is an important aquaculture specie in China.An oral administration trial and an 8-week growth trial were carried out,and growth performance,feed efficiency, blood biochemistry,liver characteristic,body composition as well as gluconeogenetic and lipogenic enzymes in fish livers were determined.First,fishes(average weight:178±10g) were fasted for 4 weeks and then oral-administrated with three different dosages of soluble starch(Ⅰ:111.4mg starch per 100g body weight,Ⅱ:222.8mg starch per 100g body weight,Ⅲ:334.2mg starch per 100g body weight),which was to investigate the digestion and glucose tolerance of gibel carp,and to provide a reference for the contents of dietary starch in the growth trial. Blood samples were collected to determine the plasma glucose and the plasma triglyceride contents before(Oh) and 1h,2h,4h,6h,8h,10h,12h,16h and 24h after being orally administered.Second,an 8-week growth trial was carried out in a recirculation system to investigate the effect of high dietary starch levels on growth performance,blood chemistry,glucose metabolism and body composition of gibel carp.Five isoenergetic and isonitrogenous experimental diets were compounded with different starch levels,which were 24%,28%,32%,36%and 40%,respectively.Corn starch andα-starch were chosen as the carbohydrate sources in the diets and the carbohydrate contents were established according to the the results of the oral-administration trial.Triplicate groups of fish (average body weight:8.5g/fish) were assigned to each of the five groups of experimental diets.The results are shown as follows:The plasma glucose contents of three groups increased significantly(P＜0.05) at 1h and peaked at 6h in groupⅠ(20.38mmol/L),at 4h in groupⅡ(21.43mmol/L) and groupⅢ(22.47mmol/L) after starch oral administration,respectively,then decreased significantly(P＜0.05),but were higher than that at Oh.Also,the plasma glucose increased significantly(P＜0.05) with the starch level oral administrated.The plasma triglyceride of three groups increased significantly(P＜0.05) and peaked at 1h(1.91mmol/L,2.07mmol/L,1.92mmol/L) after starch oral administration,then decreased to the level lower than initial(P＜0.05).The growth trial results showed that no significant difference of liver hexokinase activities,plasma triglyceride contents,body crude protein,ash and Ca,P contents was observed between different treatments.The growth performance,body crude lipid and plasma glucose concentrations showed a decreasing trend with the dietary starch increasing from 24%to 40%.The Pyruvate kinase activities and liver lipid content showed an increasing tend with the dietary starch increasing from 24%to 32%,then a decreasing tend with the dietary starch increasing from 32%to 40%.In conclusion,higher dietary starch levels(32-40%) significantly(P＜0.05) decreased the growth of gibel carp.In summary,the following conclusions could be reached:(1) The plasma glucose contents of fish oral-administrated with 334.2mg starch per 100g body weight decreased slowly and showed consistently high glucose levels for two hours after the peak time.This suggests that gibel carp had poor glucose tolerance and could not to resynthesize glycogen under this oral-administration dosage.(2) The lower content of dietary starch in the growth trial was compounded to 22%, which was according to the reference of the oral-administrated with 334.2mg starch per 100g body weight dosage.And the gibel carp still showed high FR,SGR,FE and PRE in the growth trial,which suggests that acclimation and rational formulation dietary can improve the capacity of dietary starch utilization.(3) Dietary starch level had no significant effect on body composition but body lipid content in the present study,which increased first and then decreased as dietary starch level increased to 32%which suggests that the lipogenesis could be activated only in a limited range by the dietary carbohydrate level,and a large portion of the absorbed glucose were readily excreted instead of involved in lipogenesis if exceed this range.(4) The PK activities in the present study were affected significantly but HK not affected by the increasing dietary starch,confirming that HK is not the effective index under nutritional regulation in gibel carp.(5) Overloading starch(≥32%) to the gibel carp diet(gross energy is about 19.7kJ/g) would inhibit fish growth by depressing feed intake and feed efficiency as well as PK activities.So,for normal growth of gibel carp,the starch level in the diet should be less than 32%.