| Protein is a vital nutritional factor for the growth and development of aquatic animals.Fishmeal has always been an indispensable source of high-quality protein in aquatic feed.The demand for total protein and fishmeal in Chinese mitten crab feed is gradually increasing,while the current research on dietary protein level and fishmeal replacement in Chinese mitten crab has been focused on the juvenile crab,and the fishmeal substitute is mainly a single protein source or plant protein mixture,there is a knowledge gap of protein level and new protein sources in the fattening stage feed.Therefore,this experiment has studied the suitable protein level of feed in the fattening stage of Chinese mitten crab and the application of new plant and animal protein mixtures in the juvenile and fattening stages of Chinese mitten crab.It is expected to provide a basis for the development and optimization of Chinese mitten crab feed.1.Effects of dietary fishmeal replacement with protein mixtures on growth performance,physiological metabolism and proximate composition of juvenile Chinese mitten crab（Eriocheir sinensis）It was investigated the effects of different levels（0%,16.67%,33.33%,50%and66.67%,represented as Diet 1#～5#treatments）of fishmeal replacement by protein mixtures on the survival,growth,physiological metabolism and body composition of juvenile Chinese mitten crab（Eriocheir sinensis）.The results showed that:（1）the final body weight,weight gain rate,specific growth rate and hepatosomatic index firstly increased and then decreased with increasing dietary fish meal replacement level,and the highest values were recorded in Diet 2#treatment（P<0.05）.（2）The highest levels of glutamic-oxalacetic transaminase（GOT）,glutamic-pyruvic transaminase（GPT）and malondialdehyde in hepatopancreas were detected in Diet 4#treatment,while Diet 1#treatment had the highest activity of superoxide dismutase（SOD）in hepatopancreas（P<0.05）.The highest activity of GPT in the serum was detected in Diet 5#treatment,and the highest triglyceride（TG）content and SOD activity were detected in Diet 4#treatment,while the highest malondialdehyde（MDA）content was detected in Diet 2#treatment.（3）The contents of crude protein and crude lipid in the juvenile crab’s body in Diet 1#treatment were significantly higher than those in the other treatments,while the highest total carbohydrate content was detected in Diet 2#treatment.For the amino acids composition of body,the highest cysteine（Cys）content was detected in Diet 4#treatment,and the highest contents of other amino acids and total amino acids（TAA）were detected in Diet 2#（P<0.05）.In conclusion,excessive dietary fishmeal replacement（33%-67%）reduced the growth performance and nutrients accumulation in the body of juvenile crab’s and had a negative effect on physiological metabolism.The appropriate dietary fishmeal replacement level is suggested to be about 16.67%.2.Effects of dietary fishmeal replacement with protein mixtures on growth performance,physiological metabolism and proximate composition of male and female sub-adult Chinese mitten crab（Eriocheir sinensis）It was investigated the effects of different levels（0%,16.67%,33.33%,50%and66.67%,represented as Diet 1#～5#treatments）of fishmeal replacement by protein mixtures on the growth performance,physiological metabolism and proximate body composition of sub-adult Chinese mitten crab（Eriocheir sinensis）cultured in earthen pond.The results showed that:（1）there was no significant difference in the survival and growth of crabs in all treatments.（2）The hepatosomatic index and total lipid content of males increased,while the crude protein content decreased with fishmeal replacement.However,the gonadosomatic index,meat yield,total edible yield and their respective nutritional compositions were minimally affected in both males and females.（3）The serum GOT and GPT activity of male and female crabs in Diet 5#treatment were significantly highest,while the hepatopancreas MDA content of males fed Diet 4 was highest.（4）The economic analysis demonstrated that the highest production value and partial gross returns were apparent in Diet 4#treatment.This study suggests the optimal level of fishmeal replacement was 33%and 50%for male and female crabs,respectively.3.Effects of dietary protein level on growth performance,gonadal develpoment,physiological metabolism and proximate composition of male and female sub-adult Chinese mitten crab（Eriocheir sinensis）This study assessed the effects of dietary different protein levels(278,323,351,390 and 420 g kg-1,represented as Diet 1#～5#treatments)on the growth,gonadal develpoment,physiological metabolism and proximate composition of sub-adult Chinese mitten crab（Eriocheir sinensis）cultured in earthen pond.The results show that:（1）The performance of all crabs in ponds showed bell-shaped trend,and a regression analysis provided an estimate of～384 g kg-1 dietary protein for maximal growth for female animals.Whereas,～420 g kg-1dietary protein for male crabs.（2）The GSI of female crabs at 128d and HSI at 95d showed a trend of first rise and then decrease with the increase of dietary protein level,and the highest values were recorded in Diet 2#treatment,while there was no significant difference in GSI of male crabs.（3）The hepatopancreas total lipid and gonad carbohydrate content of male crabs decreased with protein level increasing,while the hepatopancreas ash content increased significantly.The hepatopancreas crude protein and ash content of female crabs decreased first and then increased,while the lipid content showed an opposite trend and the highest value was recorded in Dite 2#treatment.（4）The serum GOT and GPT activity of male crabs showed a downward trend with dietary protein level increasing,and the highest value was detected in Diet 2#,while the serum GOT and GPT activity of females decreased first and then increased and the lowest value was found in Diet 4#.The hepatopancreas TG content of female and male crab was highest in Diet 2#and Diet 3#,respectively.（5）The serum T-AOC activity and MDA content male crab decreased with the increase of dietary protein level,while the serum T-AOC,GR activity and hepatopancreas MDA content female crab decreased first and then increased,and the lowest values were all recorded in the Diet 3#treatment.These results suggested that suitable protein levels improve overall growth and reduce hepatopancreas lipid deposition and hepatic damage,as well as oxidative stress in the body.It is concluded that the optimal dietary protein levels in the diets for female and male sub-adult crabs reared in earthen ponds are 384and 420 g kg-1,respectively. |
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