Effect Of Dietary Carbohydrate Levels On The Growth Performance, Body Compositions And Carbohydrate Metabolic Enzymes Activities In Juvenile Yellow Cheek Carp (Elopichthys Bambusa)

The present study was conducted to investigate the effect of dietary carbohydrate levels on the growth performance, body compositions and carbohydrate metabolic enzymes avtivities in juvenile yellow cheek carp(Elopichthys bambusa). These basic data were expected to evaluate the carbohydrate utilization ability and provide useful references for nutrient requirement for yellow cheek carp.Total 306 juvenile yellow cheek carp with initial weight 7.72±0.87g were allotted into 6 groups randomly. Six isonitrogenous (45% crude protein) and isolipidic (8% crude lipid) diets were formulated to contain grade carbohydrate levels (0%,5%,10%,15%, 20% and 25% respectively). White fish meal and casein were used as protein sources, fish oil as lipid source and a-starch as carbohydrate source. Each diet was considered to be one treatment and each treatment had three replicates. Animals were fed at ad libitum ration level twice daily (7:00 and 16:00 hours) for 8 weeks. The results were as follows:1. Effect of dietary carbohydrate levels on the growth performance and relative weight of carcass in juvenile yellow cheek carpThe weight gain(WG), specific growth rate(SGR) and protein efficiency ratio(PER) showed an increasing trend with the dietary carbohydrate level not more than 20%, and a decreasing trend at a higher level(P<0.05). Fish fed diet with 20% carbohydrate level exhibited significantly higher WG, SGR and PER than other groups(P<0.05). No significant difference in feed efficiency(FE) was observed among dietary treatments(P>0.05). Feeding rate(FR) increased as the dietary carbohydrate level increasing,20% and 25% carbohydrate groups exhibited significantly higher FR than other four groups(P<0.05). Dietary carbohydrate levels significantly affected the relative weight of carcass. Higher viscerosomatic index(VSI), hepatosomatic index(HSI) and intraperitoneal fat ratio(IPF) were observed in fish fed diet with 20% and 25% carbohydrate diet(P<0.05). 2. Effect of dietary carbohydrate levels on body compositions (wet weight basis) of juvenile yellow cheek carpAs dietary carbohydrate level increased, crude lipid accumulation in liver and whole body showed an increasing trend (P<0.05), but a minor effect on crude lipid content in muscle(P>0.05). The whole body proximate analysis showed that dry matter content was increased with dietary carbohydrate levels increasing, and significantly higher level was observed in 20% and 25% groups(P<0.05). Fish fed 5%,10% and 15% carbohydrate level diet had markedly more ash content compared with other groups(P<0.05). Dry matter and crude protein content in muscle were enhanced with increasing level of dietary carbohydrate,20% and 25% groups had higher content than 0% and 5% groups(P<0.05). Liver glycogen accumulation was positively correlated with dietary carbohydrate content when the dietary carbohydrate level did not exceed 20%, but decreased at a higher level(P<0.05).3. Effect of dietary carbohydrate levels on plasma biochemical indices and carbohydrate metabolic enzymes of juvenile yellow cheek carpGlucose concentration in plasma was depressed with decreasing dietary carbohydrate content, fish fed 0% and 5% carbohydrate level diet had more glucose content compared with other groups(P<0.05). Triglyceride and cholesterol concentration were no remarkable difference among dietary treatments(P>0.05). HK and PK activities were significantly induced by dietary carbohydrate levels, and showed an increasing trend with dietary carbohydrate contents increasing(P<0.05).15%,20% and 25% carbohydtate groups had higher HK activities than other groups(P<0.05). However, PK was depressed when dietary carbohydrate level exceed 10%(P<0.05). There was no negative correlation between dietary carbohydrate levels and FBPase activity. However, with carbohydrate levels increased, FBPase activity was surprisingly promoted(P<0.05). G6PDH activity was remarkedly increased when fish fed high carbohydrate content diet (20%,25%). 4. Effect of dietary carbohydrate levels on digestive enzyme activity of juvenile yellow cheek carpIntestinal digestive enzymes(protease, amylase, lipase) activities were positively related with dietary carbohydrate concentration when its incorporation was not more than 15%, and exhibited a decreasing trend at a higher level(P<0.05). Fish fed 10% and 15% carbohydrate groups showed higher protease, amylase and lipase activity than other groups, with 0% and 25% groups lowest digestive enzyme activities observed(P<0.05).In conclusion, yellow cheek carp can partly utilize carbohydrate such as starch as energy source, and its suitable supplementation should be 15%-20%. Excessive dietary carbohydrate would enhance relative weight of carcass, which was related to unhealthy growth. When encountering high carbohydrate nutrition condition, yellow cheek carp was lack of effective gluconeogenesis regulation, but it correspondingly accelerated glycolytic activities and increased synthesis of glycogen and lipid so as to moderate the hyperglycemia ater feeding and maintain plasma glucose and glycogen concentration to be a low limit. After 8-week acclimatization, dietary carbohydrate content could induce protease, amylase and lipase activities in gut, but their activities were repressed by high dietary carbohydrate level. The adjustment of intestinal digestive enzymes reflected an adaptive response for different dietary carbohydrate content in yellow cheek carp.