Dietary Methionine Requirement Of Red Swamp Craysh(Procambarus Clarkii) And Macrobrachium Nipponense

This study was conducted to determine the effects of dietary methionine levels on growth performance, feed utilization, body composition, muscle amino acids composition and digestive enzyme activities of red swamp crayfish (Procambarus clarkii) and Macrobrachium nipponense, aiming to determine the optimal dietary methionine requirement of this species, in order to provide theoretical basis for optimizing the feed formular for Procambarus clarkii and Macrobrachium nipponense, which included two series:Series 1 Dietary methionine requirement of red swamp crayfish (Procambarus clarkii)This experiment was conducted to evaluate the effects of dietary methionine levels on growth performance, feed utilization, body composition, muscle amino acids composition and digestive enzyme activities of red swamp crayfish "(Procambarus clarkii), aiming to determine the optimal dietary methionine requirement of this species. Six isonitrogenous (28.25% crude protein) and isocaloric (16.07 kJ/g gross energy) diets were formulated with the protein sources originated from casein, gelatin, fish meal, wheat glutenand and crystalline amino acid (AA) mixture. The measured methionine levels of the experimental diets were 0.39%,0.53%,0.71%,0.86%,0.98% and 1.13%, respectively. The dietary AA pattern, except for methionine, was applied to the muscle AA pattern of this species. Each diet was fed to four groups of 12 crayfish with an average initial body weight of 9.80±0.15 g in floating net cages (60×60 ×60 cm). Crayfish was fed three times daily for 56 d. The results indicated that weight gain rate, specific growth rate and feed efficiency ratio all increased significantly (P<0.05) as dietary methionine levels increased from 0.39% to 1.13% with their maximum values all being attained at 0.86%, respectively. However, they all decreased with further increasing dietary methionine levels. Survival rate ranged from 83.33% to 91.67%, and showed no significant difference (P>0.05) among all the dietary treatments. The highest whole-body protein content was observed in crayfish fed 0.86% dietary methionine. It was significantly (P<0.05) higher than that of crayfish fed 0.39% dietary methionine, but showed little difference (P>0.05) with that of the other treatments. No significant difference (P>0.05) was found in whole-body moisture, ash and lipid content and liver composition and muscle AA contents among all the treatments. The muscle lipid content of crayfish fed 0.98%dietary methionine was significantly (P<0.05) lower than that of crayfish fed 0.39% dietary methionine, but showed little difference (P>0.05) with that of the other treatments. Intestinal protease activities increased significantly with increasing dietary methionine levels(P<0.05), whereas the opposite was true for lipase and amylase activities. The second-order regression analysis of WGR against dietary methionine levels indicated that the optimal dietary methionine requirement of red swamp crayfish was 0.94% of diet (and 3.36% of diet protein).Series 2 Dietary methionine requirement of Macrobrachium nipponenseThis experiment was conducted to evaluate the effects of dietary methionine levels on growth performance, feed efficiency ratio, body composition, muscle amino acids composition and liver digestive enzyme activities of Macrobrachium nipponense, aiming to determine the optimal dietary methionine requirement of this species. Six isonitrogenous (36.07% crude protein) and isocaloric (18.09 kJ/g gross energy) diets were formulated with the protein sources originated from casein, gelatin, fish meal, wheat glutenand and crystalline amino acid (AA) mixture. The measured methionine levels of the experimental diets were 0.38%,0.47%,0.56%,0.64%,0.75% and 0.88%, respectively. The dietary AA pattern, except for methionine, was applied to the muscle AA pattern of this species. Each diet was fed to four groups of 50 Macrobrachium nipponense with an average initial body weight of 0.30 g in floating net cages (0.6m×0.6m×0.6m). Macrobrachium nipponense was fed three times daily for 56 d. The results indicated that weight gain rate, specific growth rate and feed efficiency ratio all increased significantly (P<0.05) as dietary methionine levels increased from 0.38% to 0.88% with their maximum values all being attained at 0.64%, respectively. However, they all decreased with further increasing dietary methionine levels. The highest whole-body protein content was observed in Macrobrachium nipponense fed 0.64% dietary methionine. It was significantly (P<0.05) higher than that of Macrobrachium nipponense fed 0.38% dietary methionine, but showed little difference (P>0.05) with that of the other treatments. No significant difference (P>0.05) was found in whole-body moisture, ash and lipid content and muscle AA contents among all the treatments. Liver protease activities were significantly(P<0.05) affected by dietary methionine levels, whereas the opposite was true for lipase and amylase activities.The second-order regression analysis of WGR against dietary methionine levels indicated that the optimal dietary methionine requirement of Macrobrachium nipponense was 0.70% of diet (and 1.94% of diet protein).