Optimal Dietary Protein To Energy Ratio And Utilization Of Plant Protein Sources Of Juvenile Chinese Mitten Crab Eriocheir Sinensis

Chinese mitten crab (Eriocheir sinensis) is an unique aquatic famous species for aquaculture and occupies an important position in Chinese freshwater fisheries. With the continuous expansion of crab farms and artificial feeds, the increasing demand for fish meal by aquaculture industry makes fish meal an increasingly expensive and limiting commodity. Therefore, it is important and urgent to explore the suitable methods to replace fish meal for sustaining aquaculture development. Studies have shown that the optimum protein to energy ratio (P/E) would promote the growth performance and the protein conversion efficiency, eventually reduce the farming cost of aquatic animals. In addition, since vegetable protein sources have lots of advantages, such as wide variety of sources, stable production, low-cost, use of vegetable protein sources (soybean meal, cottonseed meal, etc.) in diet to replace fish meal is an effective way to reduce the amount of fish meal.This study explored the optimal protein to energy ratio and the protein sparing effects of dietary lipid. Tthe effects of four commonly used plant proteins (soybean meal, fermented soybean meal, cottonseed meal and rapeseed meal) with or without methionine and lysine supplementation on growth performance, body composition, amino acids retention rate and antioxidant enzyme activities of E.sinensis were evaluated The results obtained in this study provide a theoretical basis for sparing fishmeal and the development of artificial feed for E. sinensis. The main results and conclusions were summarized as follows: 1 Effects of dietary protein to energy ratios on growth performance, body composition and digestive enzyme activities in Chinese mitten-handed crab, Eriocheir sinensisNine practical diets containing three protein levels (30,35 and 40%) and each with three lipid levels (2,7 and 12%) were fed to four replicates of 30 crabs(3.39±0.10 g) for 10 weeks. Results showed the survival rate ranged from 79.17% to 89.16% with no significant differences among all experimental groups (P>0.05).Weight gain rate, specific growth rate, feed conversion ratio and protein efficiency were significantly affected by the dietary protein and lipid levels(P<0.05),but not by the interaction of both(P>0.05).Weight gain increased significantly with the increasing protein level at each lipid level,and also increased with the increasing lipid level from 2 to 12% at the 30 and 35% protein level. However, the diet containing 40% protein and 12% lipid levels significantly decreased the growth performance and protein efficiency of the crabs. For the whole body composition, there were no significant differences in the whole crab moisture and ash (P>0.05). The whole crab protein content was significantly increased with the increased protein and lipid levels (P<0.05), and the whole crab and hepatopancreas lipid contents also increased as dietary lipid increased, but not dietary protein. The digestive enzymes (total protease, lipase and amylase) activities were significantly influenced by the different dietary P/E ratios. The total protease activity increased significantly with the increase of dietary protein at each lipid level. The lipase activity was statistically comparable among different dietary lipid levels at each protein level. The amylase activity was generally higher at higher dietary lipid levels, but only crabs fed the 30% dietary protein depicted significant differences in amylase activity among the three dietary lipid levels. Taken together, the crab fed the diet containing 35% protein and 12% lipid levels with P/E 15.77 mg KJ-1 revealed optimal growth, feed utilization efficiency and digestive enzymes activities. Moreover, our study indicated that the higher dietary lipid level at a relatively lower dietary protein level could provide protein-sparing effect in Eriocheir sinensis.2 Effects of four commonly used plant protein sources on growth performance, body composition, amino acids retention rate and antioxidant enzyme activities of juvenile Chinese mitten crab, Eriochier sinensisThis study investigated partial replacement of fishmeal (FM) by four commonly used plant protein sources in juvenile Chinese mitten crab. The basic diet contained 50% fishmeal and four test diets were prepared in which 50% of fishmeal was replacement by 30.50% fermented soybean meal (FSBM),32.50%soybean meal (SBM),28% cottonseed meal (CSM) and 39% rapeseed meal (RSM). Each diet was fed to four replicates of juvenile E. sinensis (0.249±0.003g) for 8 weeks. The results showed that no significant differences were found in weight gain, specific growth rate, feed conversion ratio, protein efficiency and protein retention between the three test diets (FSBM, SBM, and CSM) and FM. The weight gain of E. sinensis fed on RSM was also not significantly different from FM, but was significantly lower than those fed on SBM (P<0.05). In addition, feed conversion ratio of E. sinensis fed on RSM was significantly higher than those fed on FM, FSBM and SBM. Protein efficiency and of E. sinensis fed on RSM were significantly lower than those of crabs fed on all other groups (P<0.05). Protein retention of E. sinensis fed on RSM were significantly lower than those of crabs fed on SBM and CSM (P<0.05). There were no significant differences in the whole crab body moisture content, ash content, crude lipid content and total essential amino acids retention of the four plant protein sources groups in comparison with FM. However, the whole crab crude protein content in crabs fed on RSM was significantly lower than that of crabs fed on SBM and CSM (P<0.05). The total essential amino acids retention in crabs fed on RSM was significantly lower than that of crabs fed on FSBM and CSM (P<0.05). Superoxide dismutase and glutathione peroxidase activities in both serum and hepatopancreas of crabs were not significant different for all the four plant protein sources diets in comparison with FM diet. The serum malonaldehyde content of RSM was significantly higher than all other groups (P<0.05). The results indicated that the diets in which FM was partially replaced with FSBM, SBM and CSM did not have any negative effects on growth performance, amino acids retention and antioxidant enzyme activities of juvenile Chinese mitten crab. Thus, fermented soybean meal, soybean meal and cottonseed meal can be used as alternative plant protein sources to partially replace fishmeal in diets for Chinese mitten crab up to 30%. However, rapeseed meal is not a suitable plant protein for partial replacement of fishmeal possibly due to lower protein digestion, many anti-nutritional contents and the higher amount used. In case where rapeseed meal must be used, we suggest that it should be used in combination with other plant protein sources and/or the detoxification process should be done before its use.3 Effects of four commonly used plant protein sources by supplemented with methionine and lysine on growth performance and amino acids retention in juvenile Chinese mitten crab, Eriochier sinensisIn accordance to chapter III of feed formulation and essential amino acids contents in SBM,CSM and RSM groups and the FM control diet, the other three plant protein source diets added methionine and lysine respectively to 0.92% and 2.32% according to the measured value(recorded as SBM+,CSM+and RSM+).Totally seven experiment diets were fed to the juvenile Chinese mitten crabs (0.249±0.003g) to evaluate the effects of methionine and lysine on the plant protein sources diets for eight weeks. The results showed that there was no significantly difference in survival among all treatments (P>0.05). The weight gain rate and specific growth rate for crabs fed diets SBM+ and CSM+ was significantly higher than those of the FM group(P>0.05),while there were no significantly difference between the other groups and FM group. Feed conversion rate for crabs fed diet RSM group was significantly higher than those of the FM and RSM+ groups (P>0.05). There were no significantly difference between the test groups and FM group on protein efficiency and protein retention, but RSM group was significantly lower than SBM and CSM groups while RSM+ group was no significantly different from SBM and CSM groups. The same phenomance was also seen in the whole crab body protein content. As for the methionine and lysine rentention rate, the RSM group was significantly lower than FM and RSM+ group. Superoxide dismutase and glutathione peroxidase activities in serum were not significant different for all test diets in comparison with FM diet,but the serum malonaldehyde content of RSM was significantly higher than FM group(P<0.05). All these results indicated that the crabs’ growth performance can be improved and the amino acids composition of plant protein sources can be optimized by supplemented with methionine and lysine in the plant protein source diets. Especially in the diet with 39% rapeseed, which had negative effects on the growth performance, feed conversion ratio, protein efficiency ratio and protein retention. Although the crabs fed with 32.5% soybean meal and 28% cottonseed meal didn’t have negative effects on the growth performance, the growth performance of E. sinensis can be enhanced after supplemented with methionine and lysine.