Suitable Protein Source And Enzyme Hydrolyzed Protein Addition Level In The Seed Feed Of Largemouth Bass

Largemouth bass(Micropterus salmoides),as a freshwater economic fish,is very popular among farmers and consumers because of its short breeding cycle and delicious meat quality.In production,carnivorous fish are changed from live feeding to feed through artificial domestication to ensure controllable breeding.However,juvenile fish digestive ability is weak,early feeding feed will limit its growth rate and bone development,damage economic benefits.Protein source is the main component of aquatic feed and the core factor that determines the digestion of larvae.The protein adapted to cultured fish species is easy to be digested and absorbed by fish for their own growth and development,however,there are few studies on the selection and optimization of protein source of largemouth sea bass seedlings.By exploring the effects of different protein sources on the growth performance,body composition,digestive ability and growth related gene expression level of larvae,this experiment aims to screen the feed protein sources suitable for the digestive ability of larvae and ensure their growth in the domestication stage.At the same time,the suitable protein source was further hydrolyzed in vitro and added to the feed according to different addition levels.The effects of different levels of hydrolyzed protein addition on the growth,bone development,digestive ability,antioxidant ability and growth related gene expression level of larvae during domestication were analyzed,in order to explore the suitable addition level of feed hydrolyzed protein to improve feed digestibility and maximize the growth performance of larvae.The results are as follows:1.Study on the suitable feed protein source of larval bassIn this experiment,three micropartdiet(50% crude protein,14% crude lipid),were prepared with different protein sources(FM,KM,SM),and brine worms(Artemia,AR)were used as the control group,and a commercial microparticle feed(Commercial Diet,CD)was selected as the control group of commercial feed for 28 days in the circulating water system.The results showed that the final weight of larvae in AR group was particularly higher than that in other groups,followed by SM group,which was particularly higher than that in CD group,FM group and KM group.There was no statistical significance among the three groups.The specific growth rate(Day1-8)of AR group was the highest,which was particularly higher than that of other groups.The specific growth rate(Day13-28)of AR group was particularly lower than that of SM group,which was particularly higher than that of CD group,FM group and KM group.The feed conversion rate of larval black bass in SM group was particularly higher than that in CD group,FM group and KM group,and there was no statistical significance among the three groups.The analysis of larval body composition showed that there was no statistical significance in larval body protein content between AR group and SM group,which was particularly higher than CD group,FM group and KM group.The analysis of digestive related enzyme activity showed that the trypsin activity of AR group was particularly higher than that of other groups,followed by SM group,which was particularly higher than that of CD group,FM group and KM group.There was no statistical significance among the three groups.The m RNA expression in AR group was particularly higher than that in other groups,followed by SM group,which was particularly higher than that in CD group,FM group and KM group.There was no statistical significance among the three groups.The feed essential amino acids and essential fatty acids of FM group,KM group and SM group met the optimum requirements of larvae.Based on the above experimental results,SM is more suitable as the main protein source of largemouth bass feed.It improved the trypsin activity and induced the expression of growth-related genes,which achieved better growth and improved the feed conversion rate.Although the final body weight fell behind the AR group,it showed better growth potential.2.The optimum additive amount of hydrolyzed squid protein in feedIn this study,hydrolyzed squid protein was prepared by enzymatic hydrolysis of squid in vitro with protease,and six kinds of microdiets with hydrolyzed squid protein addition levels(0%,2%,4%,8%,16%,32%)were prepared.Artemia(AR)was used as biological bait,and the control group was fed with larvae in circulating water system for28 days.The body weight of each group was particularly lower than that of the other groups(32%,8% and 4%,no statistical significance).The larval specific growth rate(Day13-28)in the 32% group ranked first in the hydrolyzed protein group,higher than in the AR group.Bone development and feed conversion rate among 8%,16% and 32%groups is no different,which was particularly higher than that of AR group,There was no statistical significance in trypsin activity between groups,and there was no statistical significance in chymotrypsin activity and lipase activity between 0% group and 2% group,which was particularly lower than that in 4%,8%,16% and 32% groups.The activities of superoxide dismutase and catalase in larvae increased with the increase of hydrolyzed protein substitution,and reached the peak at 8%.There was no statistical significance between AR group and 0% group and 2% group,which was lowest in other groups;Glutathione activity increased with the increase of hydrolytic protein substitution.There was no statistical significance between AR group and 2%,4% and 8% groups,which was particularly higher than 0% group and particularly lower than 16% and 32% groups.The expression of m RNA in AR group was particularly higher than that in other groups.There was no statistical significance between 0% group and 2% group,which was particularly lower than that in 4%,8%,16% and 32% groups.There was no statistical significance among the four groups.Based on the above experimental results,the replacement amount of 8% hydrolyzed squid protein can maximally induce the digestive related enzyme activity and growth related gene expression of larvae,improve the growth of larvae,participate in the biochemical reaction of the body,induce the antioxidant related enzyme activity of larvae and improve the immune level of the body.In conclusion,the addition of an appropriate amount of hydrolyzed protein in the feed not only promoted the growth of larvae,but also improved the immunity level and reduced the rate of seedling malformation.The results showed that the suitable addition level of hydrolyzed squid protein in the feed was 8%.