EFFECTS OF DIETARY PROTEIN AND WHEAT STARCH ON GROWTH AND LIVER STRUCTURE OF GRASS CARP, CTENOPHARYNGODON IDELLA

To study effects of dietary carbohydrates and proteins on the growth of grass carp, we formulated a factorial design of 2×4 diets with medium-size (460 g) and large-size (1970 g) grass carp (Ctenopharyngodon idella). Two die-tary starch levels of 25% and 35% and four protein levels of 22%, 24%, 26% and 28% were fed with medium-size grass carp for 56d with same quantity of food. Two dietary starch levels of 30% and 40% and four protein levels of 18%, 20%, 22% and 24% were fed large-size grass carp. The results showed that the growth performance of the medium-size grass carp increased significantly with increased protein level with the highest effect in the 28% protein group (P<0.05), and the growth performance of 35% wheat starch group was significantly higher than that of the 25% group (P<0.05). The growth performance of large-size grass carp increased significantly with the increased protein level with the peak level at 20% (P>0.05). The growth performance of the 40% wheat starch group was significantly higher than that of the 30% group (P<0.05). No significant negative effects on liver tissues were observed by adding 35% or 40% wheat starch in both groups of grass carp. These results revealed that grass carp can effectively utilize starch to save feed protein when the wheat starch level of the feed was below 35% and 40%, respectively.