Study On The Optimum Dietary P/E For Juvenile Topmouth Culter

The purpose of this research was to search an optimum dietary P/E level for juvenile Topmouth Culter, Culter alburnus, considering about the growth performance, digestive enzyme activities, and serum biochemical indicators. Then we probed into the effects of dietary P/E on body composition and muscle content of juvenile Topmouth Culter to make sure that the optimum dietary P/E we obtained can also be helpful to muscle quality. So we divided the research into two experiments.In experiment 1, nine experimental diets with different dietary P/E ratios (varying from 23.50 to 30.90 g/MJ) were formulated to contain three protein levels (45%,40% and 35%), with each having three lipid levels (5%,8% and 11%) respectively. The diets were fed to triplicate groups of fish in cages (30 fish per cage) for 56 d, and experimental fish were fed to apparent satiation twice a day. After 8 weeks of farming in a lake,10 experimental fish of every cage were captured randomly and collected to be analyzed. The results showed that dietary P/E effected the growth performance of juvenile Topmouth Culter significantly, the weight gain rate (WGR), special growth rate (SGR), hepatosomatic index (HSI) and viserosomatic index (VI) among groups were different significantly (P<0.05). The specific growth rate (SRG) varied as the dietary P/E follow the type of decreasing after increasing with the maximum in group D5 (P/E， 27.79 g/MJ), which showed no significant difference (P>0.05) with group D4, D6, D7 in SRG. The protease activity of both hepatopancreas and intestine decreased after increasing with the increase of dietary P/E, the highest protease activity of intestine showed in group D4, different from SRG having the highest value in group D5. Though the regularity of the variations of lipase activity of intestine as dietary P/E increased was not so obvious, we noticed that the lipase activity in intestine in groups with lowest dietary lipid level (5%) were much lower than that of higher groups (8%,11%). The dietary P/E showed no significant effects (P>0.05) on amylase activity of both intestine and hepatopancreas. The ALT in serum of experimental fish showed the highest activity in Group D9, which was strongly significantly higher than that of other groups. The proteins including TP, ALB, GLO in serum showed significant difference among groups, but the range of the changes was relatively small and the variation through dietary P/E was not obvious. The content of TG and GLU in groups with highest dietary lipid were significantly high than that of other groups.In experiment 2, fish from experiment 1 after farming were analyzed on the body composition and muscle composition and some indexes of flesh quality. The results showed that the dietary P/E have no significant effect (P>0.05) on body water, body ash and body protein contents of juvenile topmouth culter. Body lipid showed the trend of varying from dietary lipid levels, groupD8 and D9 with 11% dietary lipid level. But the content of water, ash, protein and lipid in muscle showed significant difference among groups (P<0.05). Groups with higher dietary protein have a higher protein level of muscle, groups with 45% and 40% dietary protein showed no significant different between each other in protein content in muscle but all were higher than that of 35% groups. The variation of lipid content in muscle from dietary P/E showed similar with that of body lipid. Group D5 had the highest muscle collagen level. The muscle fibers of experimental fish were loosely packed in most groups except in group D8 and D9, which were closely packed due to the high level of lipid among them, having the smaller diameter of muscle fiber.Through the analysis of growth performance and digestive enzymes, conclusion can be concluded that the optimum dietary P/E for juvenile Topmouth Culter should be within the range of 26.32-29.03 g/MJ, and the dietary protein and lipid level be 40%,8% respectively. The analysis of body composition and muscle quality indicated that variation of dietary P/E can result in the change of flesh quality of juvenile Topmouth Culter, and the diet with 45% protein and 8% lipid can not only ensure a good growth but also much good flesh quality.