| In recent decades,the scale of Chinese mitten crab aquaculture industry expands unceasingly,brought the increase of demand for compound feed.Fish meal is widely used in animal feed for its high nutritional value and good amino acid composition.But the uneven quality and high price of fish meal make it needs to be replaced urgently.Soybean meal is rich in protein,after fermentation,the antinutritional factor were removed,and the nutrition composition and palatability were improved.Therefore,fermented soybean meal is considered to be suitable to replace fish meal.The experiment chooses two different kinds of fermented soybean meal to replace part of fish meal,respectively,to study the effects of different feeds on growth performance,whole-body composition,amino acid composition of muscle,antioxidant capacity,immunity ability and protein metabolism of Chinese mitten crab,in order to explore the optimum substitution ratio of fermented soybean meal for fish meal.The study includes the following three parts:Experiment 1 Effects of fermented soybean meal on growth performance,whole-body composition,amino acid composition of muscle of Chinese mitten crab（Eriocheir sinensis）The aim of this experiment was to explore the effects of different feeds on growth performance,whole-body composition,amino acid composition of muscle of Chinese mitten crab.Seven isonitrogenous and isolipidic experimental diets were formulated.The control diet named CON contains 30%fish meal.Other diets were prepared by replacing fish meal with two different fermented soybean meal with 5%,10%,and 15%,respectively.Accordingly,they were named as A5,A10,A15,B5,B10 and B15.A total of 168 crabs were randomly distributed into 21 cement pools at a density of 8 crabs per pool（3 replicates）.The experimental period lasted for 10 weeks,until which time almost all the crabs had shelled twice.During the feeding trial,the crabs were feed twice a day（7:00 and 19:00）.The feeding amount in the morning accounted for 1/3,and the feeding amount in the evening accounted for 2/3.In addition,the number of ecdyses of crabs was recorded daily.After the breeding cycle,one male crab and one female crab per pool were randomly selected and frozen at-20℃ for determination of the whole-body composition.After that,three crabs were sampled in per pool.Hepatopancreas of the crabs were collected completely and weighed in a sterile environment.Afterwards,the sample were stored at80℃ for deep analysis.At last,pectoral muscles of the crabs were collected and stored at20℃.The results showed that,using fermented soybean meal A to replace fish meal,with the replacement ratio increase,the final weight,weight gain rate and specific growth rate showed a firstly upward and then downward trend.In addition,when replacing 10%fish meal,the final weight,weight gain rate and specific growth rate of Chinese mitten crab were significantly increased compared with the control group.After the fish meal was replaced with fermented soybean meal B,the final weight,weight gain rate and specific growth rate of crabs increased as the substitution ratio increased,but the difference was not significant（P>0.05）.No significant difference was observed in moulting rate and hepatosomatic index in all dietary treatments（P>0.05）.The content of crude protein and crude lipid in the crabs of groups added fermented soybean meal were higher than those in the control group.The contents of various amino acids in each group varied slightly,and the differences were not significant（P>0.05）.In summary,using fermented soybean meal to replace appropriate amount of fish meal could promote the growth of Chniese mitten crab and increase the deposition of protein and lipid.Experiment 2 Effects of fermented soybean meal on serum antioxidant capabilities and non-specific immunity of Chinese mitten crab（Eriocheir sinensis）The aim of this experiment was to study the effects of using fermented soybean meal to replace fish meal on antioxidant capabilities and non-specific immunity of Chinese mitten crab.The feed and culture experiments used in the experiment were the same as experiment 1.Blood samples were collected at the end of culture to determine the antioxidant and immune indexes.The results showed that using two kinds of fermented soybean meal to replace fish meal had little effect on lipid peroxide,catalase and total antioxidant capacity in serum of Chinese mitten crab.Only lipid peroxide in B15 group was significantly lower than that in control group（P<0.05）,while the antioxidant indexes in other groups were not significantly different from that in control group（P>0.05）.There was no significant difference in the activity of acid phosphatase in serum among all the groups（P>0.05）.Except for A15 group,there was no significant difference in total protein content,albumin content and globulin content between all the groups（P>0.05）.In addition,there was no significant difference in A/G among all the groups（P>0.05）.From the above results,it can be concluded that using fermented soybean meal to replace appropriate amount of fish meal have no negative impact on the antioxidant capabilities and non-specific immunity of crabs.Experiment 3 Effects of fermented soybean meal on protein metabolic enzyme activity and related gene expression of Chinese mitten crab（Eriocheir sinensis）The aim of this experiment was to study the effects of using fermented soybean meal to replace fish meal on protein metabolic enzyme activity and related gene expression of Chinese mitten crab.The feed and culture experiments used in the experiment were the same as experiment 1.Hepatopancreaswas collected after culture,and the activities of protein metabolization-related enzyme and the expression of related genes were determined.The results showed that after the fish meal was replaced with fermented soybean meal A,the activities of trypsin,pepsin,Na+,K+-ATPase,glutamic oxalacetic transaminase and glutamic-pyruvic transaminase rose first and fell later along with the increasing of the replacement ratio of fish meal.The activities of trypsin in A5,the pepsin and Na+,K+ATPase in A10,the GPT in A10 and A15 were significantly higher than CON.Besides,after the fish meal was replaced with fermented soybean meal B,the activities of enzymes were found to be elevated.The activities of trypsin and pepsin in both B10 and B15 were significantly higher than CON.The activity of Na+,K+-ATPase in B10,was significantly higher than CON,and the glutamic-pyruvic transaminasein B15 was significantly higher,too.After the fish meal was replaced with fermented soybean meal,the expression of protein kinase B（Akt）,ribosomal protein S6 kinase 1（S6K1）and oligopeptide transporter 1（PepTl）in hepatopancreas gradually decreased with the increase of substitution,and they were all higher than the control group.The expression of 4E-binding protein 1（4EBP1）in each treatment group gradually increased with the increase of fish meal replacement ratio,and was lower than that in the control group.From the above results,we can see that using fermented soybean meal to replace fish meal can activate TOR pathway in Chinese mitten crab and promote the metabolism and absorption of protein. |
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