The effects of diet protein levels on the growth, body composition and digestive enzyme activities of the Barbodes caldwelli juvenile

Seven isoenergic semi-purified test diets containing graded levels of protein ranging from 20% to 50% were formulated using fish meal and casein as the protein sources. Triplicate groups of Barbudes caldwell juveniles with initial body weight of 1.26± 0.02 g respectively were fed by the test diets for 8 weeks. The results indicated that there was no significant effect of dietary protein levels on the survival rate, relative weight of viscera and relative weight of liver of the juvenile fish (P 0.05). The weight gain and specific growth rate of the fish were increased with dietary protein level increasing from 20% to 35% (P 0.05), but not affected significantly as dietary protein level increased from 35% to 50% (P 0.05). Feed efficiencies were not significantly different when fish fed diets with protein levels from 30% to 50%, but significantly higher than those of the other two treatments when fish fed diets with protein levels of 20% and 25% (P 0.05). The protein efficiency ratio(PER) was negatively correlated to the diet protein level(x) (PER = 3.006-0.03251x, R =0.9366). There was no significant effect of dietary protein levels on carcass moisture, crude protein and ash of the juveniles (P 0.05). While carcass lipid was decreased with the increase of dietary protein level (x) (L =8.2169-0.0458x, R =0.8551). There was no significant variation of hepato-pancreas protease activity among tests (P 0.05). Intestine protease activity and hepato-pancreas amylase activity were increased to some extent, and then decreased with continued increasing dietary protein level. The intestine amylase activity (IAA) of the juvenile was negatively correlated to dietary protein level (x) (IAA = 84.625-0.9147x, R =0.8463). It was estimated that the suitable protein level for the B. caldwell juvenile was 34% of dry diet when the broken-line model was introduced to regress the relationship of weight gain of the juvenile and dietary protein level.