| Macrobrachium nipponense is an important freshwater economic shrimp in China.It is popular among farmers because of its fast growth,strong reproductive power,strong disease resistance,and high market value.The growth rate of males M.nipponense is significantly faster than that of females.The average size of males in the same harvest period is about 2-2.5 times that of females.The whole male or single male culture can help increase production and economic benefits of M.nipponense,but there is no research on the sex differentiation of exogenous steroid sex hormones in M.nipponense.Therefore,this study took M.nipponense as the object,and studied the effects of exogenous steroid sex hormones on the growth performance,sex ratio and gonadal development of M.nipponense by adding a certain dose of steroid sex hormones to the feed.The results of the study were as follows:1.Effect of 17β-estradiol on the growth performance and gonadal development of the juvenile male shrimp,M.nipponense.In this experiment,17β-estradiol was used to feed juvenile male shrimp.Set five gradients: 0mg/kg,100mg/kg,250mg/kg,500mg/kg,1000mg/kg.The breeding cycle is 30 days.The research results show that:(1)The weight gain rate is E1000>E500>E250>E100>Control,and the specific growth rate is E1000>E500>E250>E100>Control.The weight gain rate is consistent with the specific growth rate trend.The difference between the control group,E100 and E250 gradient groups was not significant,and the difference in weight gain rate between E500 and E1000 was not significant(P>0.05).E500 and E1000 were 66.91% and 86.41% higher than the control group respectively(P<0.05).The survival rate of E500 was significantly higher than that of control group(P<0.05),but there were no significant differences among control group,E100,E250 and E1000.(2)In terms of gonadal development,histological section results showed that on day 0,the main cell types in the testes of each group were a large number of spermatogonia and a small number of spermatocytes;on day 15,spermatocytes and sperms appeared in the control group.The number of control group was significantly greater than that of the experimental group.E100 and E250 had a large number of spermatocytes and a small amount of sperm,while E500 and E1000 did not show sperm;on the 30 th day,the testis of the control group was full of sperm,while E100 and E250 still had a large number of spermatocytes and a few sperms.E500 and E1000 did not show sperm.In terms of gene expression,with the increase of hormone concentration,the relative expression of Mn SG showed a downward trend.The relative expression of the control group was significantly different from that of the experimental group(P<0.05),but there was no significant difference between the experimental groups.In terms of hormone levels,as the concentration of estradiol was increased,the testosterone content in the testis showed a gradual decrease,and the testosterone content in each experimental group was significantly lower than that in control group(P<0.05).2.Effect of 17α-methyltestosterone on the growth performance and gonadal development of juvenile female shrimp,M.nipponense.In this experiment,17α-methyltestosterone mixture was used to feed juvenile female shrimp.Set five gradients: 0mg/kg,100mg/kg,250mg/kg,500mg/kg,1000mg/kg.The breeding cycle is 30 days.The research results show that the weight gain rate is MT1000>MT500>MT250>MT100>Control.The specific growth rate is MT1000>MT500>MT250>MT100>Control.The weight gain rate was consistent with the specific growth rate trend.MT100 and MT250 were not significantly different from the control group.There was no significant difference among MT100,MT250 and control group,while MT500 and MT1000 were significantly higher than the control group(P<0.05).The survival rate of MT100 was significantly higher than that of the control group(P<0.05),but there was no significant difference among control group,MT250,MT500 and MT1000.(2)In terms of ovarian development,on days 6-9 of the experiment,the number of phases Ⅰ and Ⅱ in the control group was significantly less than that in the experimental group,and the number of individuals in phase Ⅲ and IV was more than that in the experimental group.On the 12 th day,the ovarian development period of the experimental group was mainly staying in phases Ⅲ and Ⅳ.At the same time,the number of phases Ⅲ-Ⅴ in the control group decreased,and the number of phases Ⅰ-Ⅱ gradually increased.In terms of gene expression,the expression of Vg gene in the experimental group was significantly lower than that in the control group(P<0.05).There was no significant difference between the experiment groups(P>0.05). In terms of hormone levels,the change of methyltestosterone on the estradiol content in the ovary showed a trend of first increasing and then decreasing.The hormone levels reached the maximum value of 1012.437pg/g at a treatment concentration of 250mg/kg.3.Effect of exogenous steroid sex hormones on sex differentiation of juvenile shrimp,M.nipponense.This experiment is mainly divided into three groups: control group(0mg/kg),17β-estradiol group(1000mg/kg)and 17α-methyltestosterone group(1000mg/kg).Juvenile M.nipponense with undifferentiated gonads were fed for 30 days.The results of the study showed that the female-male ratios of the control group,methyltestosterone group(1000mg/kg),and estradiol group(1000mg/kg)were 1:1.25,1:1.53,2.1:1.The female ratio of the estradiol group was significantly higher than that of control group and methyltestosterone group(P<0.05).The maleization rate of the methyltestosterone group was not significantly different from that of the control group(P>0.05).In summary,both 17β-estradiol and 17α-methyltestosterone can promote the growth of M.nipponense,and affect the survival rate of M.nipponense within the concentration range of 0-1000mg/kg;17β-estradiol can increase the female ratio of M.nipponense and inhibit the development of the testis of male shrimp;17α-methyltestosterone cannot significantly increase the male ratio of M.nipponense,but it can inhibit the ovarian development of female shrimp. |
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