Effects Of Different Domestication Time And Different Feed Feed Enzyme Preparations On The Domestication Largemouth Bass Fry

Largemouth bass,an important economic fish,which production is increasing year by year.In order to reduce the cost of breeding and the risk of bring pathogenic organisms.It is necessary to domestication by using feed to replace biological bait gradually.However,in the process of fry domestication,the following problems have been restricted the improvement of yield.First,the unclear domestication time of largemouth larvae causes a low success rate of domestication.Moreover,due to the poor digestibility and the low digestion and utilization rate of micro diets of the larvae,which results in unsatisfactory domestication results.In this study,firstly,we used the factory circulating water system to study the effects of different domestication time on the growth performance,digestive enzyme activity,antioxidant capacity and immune indicators to obtain the suitable domestication time.Then,based on the suitable domestication time and the micro-granule basal feed with the adding of exogenous enzyme preparations,we explored the effects of different enzyme preparations on growth performance,genes expression level,intestinal tissue structure,endogenous digestive enzyme activities and antioxidant ability of largemouth bass larvae.These results provides theoretical basis for the improvement of the domestication strategy of largemouth bass under industrial conditions and the application of micro diets enzyme preparations.1.Explore the suitable time for largemouth bass larvae to begin domesticationIn this study,the larvae of largemouth bass were cultured in in a circulating water system by feeding Artemia before feeding.During the experiment trial,four experimental groups were performed: After feeding with Artemia,domestication began on the 10 days after hatching(DB10);the 13 DAH(DB13);the 16 DAH(DB16)and the 19 DAH(DB19);then the commercial feed and Artemia were used together for 10 days during domestication.After the domestication,only the commercial feed was used for feeding.The experiment lasted for 28 days.These results showed that with the delay of the domestication time,the terminal weight,weight gain rate and specific growth rate of the fish gradually increased,while the deformity rate gradually decreased,and there were significant differences among the groups.However,the survival rate and the domesticating success rate of the DB16 group were highest.The activities of α-amylase,lipase,trypsin and alkaline phosphatase,also increased with the delay of the domestication time.The levels of total antioxidant capacity in the DB16 and DB19 groups were higher than those in the other groups,and the levels of acid phosphatase,alanine aminotransferase and aspartate aminotransferase were normal,indicated that the fish was healthy.The DB16 group had high growth rate,digestive enzyme activity and antioxidant capacity,low deformity rate,and the highest survival rate and acclimation success rate.Therefore,under the condition of factory circulating water,largemouth bass larvae should begin to domesticate on the 16 DAH.2.Effects of exogenous enzyme preparations in micro diet on largemouth bass larvaeBasing on the optimal domestication time,in order to further improve the effect of domestication,we explored the effect of diet on largemouth bass larvae by adding different enzyme preparations.In this study,a kind of largemouth bass larvae diet with krill meal,squid meal and fish meal was prepared.The experimental group was supplemented with 1000U/g of different enzyme preparations,and they were set as:amylase group(Amylase,Amy),lipase group(Lipase,Lip),protease group(Protease,Pro)and the mixture of the three enzymes-Compound enzyme group(Compound enzyme,Com),the feed group without enzyme preparation was used as blank control(Blank control,Bla),using only the Artemia diet as a biological bait group(Biological bait,Bio).Alpha-amylase: 350,000 U/g,lipase: 1,000,000 U/g,and protease: 250,000 U/g,all from Shanghai Mc Lean Biotechnology Co.,Ltd.Largemouth bass larvae began domestication on 8 DAH,after feeding largemouth bass larvae with Artemia for 8 days,they were divided into 6 groups.The experiment started at 10 DAH,and the domestication was lasted for 10 days.The experiment lasted for 28 days and ended on 43 DAH.The results showed that the growth rate of all the groups using the feed was faster than that of the Bio group.However,the final body weight,weight gain rate and specific growth rate of Amy,Pro and Com groups using enzyme preparations were higher than those of Bla group,while those of Lip group were lower than those of Bla group.The survival rate of the Lip group was significantly lower than that of the other feed groups,and the deformity rate was significantly increased,and the remaining groups had no significant difference.The relative m RNA expression levels of growth hormone and insulin-like growth factor 1 and the growth performance of each group kept the same trend.The tissue structure of the foregut of Amy,Pro and Com was more favorable for digestion and absorption than that of the Bla group.The a-amylase and lipase activities of Amy,Pro,and Com were enhanced,and the alkaline phosphatase activity of the Com group was also significantly increased.Enzyme activity with antioxidant activity was enhanced in both Amy and Com groups,but the opposite was true in Lip group;the level of malondialdehyde in Com group was lower,but the opposite in Lip group.The lysozyme activity of the Com group was also improved,and the non-specific immunity was enhanced.The Amy,Pro and Com groups had improved growth performance,improved foregut tissue structure,enhanced endogenous digestive enzyme activity,Amy and Com groups had improved antioxidant capacity,and Com group had enhanced non-specific immunity,while Lip had improved growth performance,digestive enzymes Negative effects in terms of activity,antioxidant and non-specific immunity.Therefore,amylase and protease are suitable additives for the open diet of largemouth bass larvae.To sum up,under the condition of factory circulating water,the optimal domesticate time was the 16 DAH.Moreover,adding amylase and protease into the micro diets would improve the domestication effect.