An experiment was conducted to determine the effect of dietary wheat starch on grass carp (Ctenopharyngodon idella) in terms of growth performance, feed efficiency and digestibility. Five isoproteic (23.5%) and isolipidic (5.7%) diets with five supplemented levels of wheat starch (D20, D26, D33, D40 and D47 with 20, 26, 33, 40 and 47%, respectively) were fed to triplicate groups of grass carp (mean initial wet weight 6.9 ± 0.1 g) for 8 weeks. Results showed that weight gain (WG, %), feed efficiency (FE, %) and protein efficiency ratio (PER) in D20, D26 and D33 treatments were significantly higher than those in D40 and D47 treatments (P \ 0.05). Digestibility of carbohydrate and protein was significantly higher in D20, D26 and D33. No significant differences were found in serum glucose and triglyceride contents between treatments. Serum lipase activity of fish fed D40 and D47 was significantly higher than that of fish fed other diets. Wholebody, muscle and liver lipid contents increased with dietary starch level as did mesenteric fat index, hepatosomatic index and viscerosomatic index. In conclusion, when dietary protein level was 23%, the level of dietary wheat starch should maximum be 33% to support normal growth of grass carp. Fish growth was hampered by higher wheat starch ([33%) despite fish ate increasing levels of dietary digestible energy. Furthermore, excess digestible carbohydrate was to some extent converted to lipid that was deposited in various tissues. Most importantly, grass carp could endure high levels of cellulose without any negative effect on growth and digestibilities of dietary protein and carbohydrate.

Problem statement: The utilization of crystalline amino acids was detected for growth performance and body composition of juvenile grass carp (Ctenopharyngodon idella). Approach: L-Lysine sulphate and Methionine Hydroxy Analog-Ca (MHA-Ca) were selected for determination. Two diets were formulated with or without amino acids supplementation. Each diet was assigned to 10 tanks in a completely randomized design for 8 weeks. Results: The results demonstrated that the final weight, Weight Gain (WG) and Protein Retention (PR) of the fish fed diet with supplemental lysine and methionine were significantly higher, while the Feed Conversion Ratio (FCR) were significantly lower in comparison with the reference group. The Condition Factor (CF) of the fish fed diet with lysine and methionine supplementation were significantly higher than the reference group (p<0.05). However, the Viscera Somatic Index (VSI), Hepato Somatic Index (HSI) and Intra Peritoneal Fat Ratio (IPFR) of the tested group were markedly lower (p<0.05). Whole body moisture and muscle protein content of the tested fish significantly increased, while the lipid level of whole body significantly decreased (p<0.05) with the supplementation of lysine and methionine. Conclusion: Results of the present investigation demonstrate significant improvement of growth and feed utilization of grass carp can be achieved by L-Lysine sulphate and MHA-Ca supplementation. WG and PR of the tested group improved 11.4% and 8.3% respectively, while FCR decreased 9.6% in comparison with the reference group (p<0.05)