Study On Muscle Growth And Digestive Performance Of Micropterus Salmoides During Early Development

In this study,histochemical,enzymatic and molecular biological methods were used to analyze the growth law and digestive performance of Micropterus salmoides during the early stage of postembryonic development,the differences in muscle nutrients and growth gene expression of Micropterus salmoides juveniles at different growth rates,and the reasons for the growth differences of Micropterus salmoides juveniles at different growth rates were explored from the aspects of digestive factors.The specific research results are as follows:1.Study on early development and growth characteristics of Micropterus salmoidesTo investigate the growth characteristics of Micropterus salmoides juveniles.The total length,body weight and main indexes of head organs of Micropterus salmoides from 3 to 27 days after membrane emergence were measured.The results show that,The relationship between full length and body weight of Micropterus salmoides was power function:L=0.00028W^4.939,R²=0.806.According to the fitting degree analysis,the curve fitting between the full length of the early development stage and the age of Micropterus salmoides conformed to the linear equation,and the relationship was y=0.332x+4.657,R²=0.997.The curve fitting of body weight and age conformed to power function,the relationship equation was y=0.002x^1.629,R²=0.990.In the head organs,head length,head height and kiss length were positive allometric growth,and eye diameter was negative allometric growth.Studies have shown that the growth pattern of Micropterus salmoides is allometric growth.Head organs also showed allometric growth characteristics relative to full length.2.Study on main digestive enzymes of Micropterus salmoides during early developmentExploring the characteristics of changes in lipase,trypsin and alpha-amylase activities in juvenile Micropterus salmoides.The results showed that lipase activity began to decrease when larvae entered the mixed nutrition period,and increased until the fluctuation of exogenous nutrition period（P>0.05）;trypsin activity increased significantly during the transition to the mixed and exogenous nutrition stages of the juvenile fish,and reached a maximum value when entering the mixed nutrition stage（P<0.05）;the activity ofα-amylase reached the maximum in the endogenous nutrition period,and decreased significantly in the mixed nutrition period,and then increased in the exogenous nutrition period（P<0.05）.Studies have shown that the high protein and fat requirements of Micropterus salmoides in their developmental stages reduces the need for sugars.3.Differential analysis of muscle nutrient composition and expression of related genes in juvenile Micropterus salmoides at different growth ratesThe differences in general nutritional components,amino acid and fatty acid,and gene expression related to muscle growth of Micropterus salmoides at different growth rates were explored.The results of the nutrient analysis showed that the moisture and crude protein of the slow-growing group were significantly higher than those of the fast-growing and medium-growing group（P<0.05）,the crude fat of the fast-growing group was significantly higher than that of the medium-growing and slow-growing groups（P<0.05）,and there was no significant change in the ash content of the fish in each group（P>0.05）.A total of 16 amino acids were detected in the muscle tissues of Micropterus salmoides,with the slow-growth group containing significantly more essential amino acids than the fast-growth and medium-growth group（P<0.05）;Fatty acid content in muscle of Micropterus salmoides at different growth rates was significantly different.Saturated fatty acid and monounsaturated fatty acid content in fast-growing group were significantly highest（P<0.05）,and polyunsaturated fatty acid content in slow-growing group was significantly highest（P<0.05）.The results of muscle growth-related gene expression showed that the expression of IGF-1 in the muscle of Micropterus salmoides in the medium-speed growth group was the highest（P<0.05）;the expression of Myo D and Myo G in Micropterus salmoides muscle of rapid growth group was the highest（P<0.05）;the expression of Myf5 was significantly highest in the slow-growing group（P<0.05）,while the expression of Myf6 was not significantly different between the groups（P>0.05）.The study showed that there were significant differences in the quality and growth of Micropterus salmoides muscle at different growth rates.The nutritional value of Micropterus salmoides muscle in the fast-growing group was not as high as that of the slow-growing group,but muscle growth gene expression was relatively high and muscle growth was faster.Therefore,to optimise the breeding of Micropterus salmoides,protein and fat supplementation should be increased during the feeding period to ensure high growth rates and good muscle quality.4.Histological observations on the intestinal tract of Micropterus salmoides at different growth rates and analysis of intestinal floraThe reason of growth rate differentiation of juvenile Micropterus salmoides was discussed from digestive factors.The results showed that:in terms of intestinal histology,the intestinal villus height and intestinal muscular thickness of the foregut,midgut and hindgut in the fast-growing group were higher than those in the slow-growing group（P<0.01）;in terms of digestive enzyme activity,the intestinal lipase activity of young fish in the fast-growing group was higher than that in the slow-growing group,with significant difference（P<0.05）;in terms of intestinal flora,the relative abundance of Actinobacteria and Halomonas in the intestine of young fish in the fast-growing group was higher than that in the slow-growing group at the phylum level.At the genus level,the relative abundance of Halomonas and Bifidobacterium communities in the fast-growing group was significantly higher than that in the slow-growing group.