Effects Of Steroid Hormones On Growth Difference And Growth-related Genes Between The Female And Male Nile Tilapia Oreochromis Niloticus

Tilapia has the characteristics of fast growth,high feeding habits and strong adaptability.Tilapia is one of the most important fresh-water aquaculture species in the world.By taking corresponding measures,Cultivation of unisexual fingerlings is important for improving the economic benefits of aquaculture.There are significant differences in growth between male and female tilapia,males grow faster than females and males are larger than females.This phenomenon appears before sexual maturity and becomes more significant after maturity partly due to the effects of sex steroids.Energy is preferentially distributed in reproduction after maturity.Estrogen that has the pleiotropic effects is a kind of steroid hormones which produced by endocrine system,which closely relates to the growth and reproduction of animals.This paper uses the Nile tilapia as the experimental object.First of all immature female and male Nile tilapia growth pattern are used as the research background,then the effects of in vitro sex steroid injection on the growth axis related genes,myogenic factors,and the regulation of the expression of feeding genes were studied.Finally,the mechanism of regulating the growth of male and female was discussed from the perspective of sex steroid receptor.This paper will describe the research from the following aspects:（1）Studies were conducted to reveal the growth differences between female and male Nile tilapia（Oreochromis niloticus）by identifying the gender with molecular marker,acid red dyeing method and histological section,meanwhile,the content of serum steroid hormones,testosterone（T）and estradiol（E₂）,were also investigated.Results showed that the total length,body weight in the female and male began to show significant differences（P < 0.05）at 3 and 2.5 months age,respectively.Simultaneously,the Logistic growth equation can be expressed as Lt（♀）=16.443/(1+e^{2.821-1.363*t}),Lt（♂）=18.248/(1+e^2.72-1.295*t),Wt（♀）=107.704/(1+e^{5.157-1.464*t},Wt（♂）=134.796/(1+e^{5.080-1.417*t}.The inflection point for the body weight growth was 3.523 month in the female and 3.585 month in the male,the corresponding weight was Wt（♀）=52.352 g,Wt（♂）=67.398 g.The growth rate of total length and body weight in the male was throughout larger than that in the female.Furthermore,the male showed longer period and heavier increment than the female in the fast-growing period.After 2.5 and 3 months age,the content of E₂ and T between the male and female was significantly different（P<0.05）,respectively.Results suggested that the relative content of E₂ and T may result in the growth difference between the male and female.（2）Nile tilapia exhibits strong sexual growth dimorphism.The potential role of sex steroid hormones in sexual growth dimorphism is not fully understood.We investigated the effects of estradiol（E₂）and testosterone（T）on growth rate,plasma sex hormones,and expression of GH-IGF axis genes and muscle-regulatory factor（MRF）genes in female and male Nile tilapia.The results revealed that serum concentrations of E₂ and T were significantly higher after correlative injection（P<0.05）.Compared to male fish,female fish had lower growth rates.E₂ increased growth performance in females with no significant effects on males,whereas T significantly increased growth performance in males with no significant effects on females.In females,E₂ significantly increased expression of ghr1,ghr2,igf1,and igf2,while T decreased igf2 and increased ghr1 and ghr2 expression.In males,T increased expression of igf1,igf2,ghr1,and ghr2,and E₂ decreased expression of igf1,ghr1,and ghr2.Additionally,E₂ and T enhanced the expression of MRF genes（myod1,myod2,myog,and myf5）in female and male fish,respectively.The results suggest that sex steroid hormones play a role in sexual growth dimorphism by regulating the expression of GH-IGF axis and MRF genes.（3）The efficacy of exogenous sex steroid hormones estradiol（E₂）and testosterone（T）was evaluated on digestive enzyme activity and expression of food intake related genes ghrelin,leptin,orexin,NPY,CCK in female and male Nile Tilapia for 6h,12 h and 24 h.In the present study,after injection treatment of 24 h,E₂ increased the activity of intestinal amylase in female and T increased the activity of the activity of intestinal amylase in male（P<0.05）.The injection of E₂ increased expression of ghrelin,NPY significantly and decreased expression of leptin in female.In contrast,T increased expression of ghrelin,、NPY significantly and ased expression of leptin in male.The results revealed that sex steroid hormones affected food intake（4）Sex steroid hormones recepter in gonad,liver,intestine,kidney was measured by the measure of Western-blot,immunohistochemistry,q PCR.Results show that the expression of ER protein in male was significantly different from female fish,ER protein expression was significantly different between in testis and ovary.ER protein expression was the highest in the gonad and there was no significant difference between male and female in intestine and head kidney.AR protein expression was significantly different in testis and ovary.Similarly AR protein expression was the highest in the gonad,and the expression of AR protein was significantly different between male and female fish in head kidney.The immunoreactivity of ER and AR were detected in gonad,intestine and head kidney of male and female fish.ER positive cells were detected in the liver of female fish,and the positive cells were mainly distributed in the vicinity of the central vein.The positive reaction of AR was stronger than ER in male fish intestine,and the positive cells were mainly distributed in the intestinal villi and intestinal submucosa.The positive reaction of ER was stronger than AR in female fish head kidney,and the positive cells were mainly distributed in the renal tubules.Positive cells in ovarian were distributed around the follicle,and the positive cells in testis were distributed around seminiferous tubule.Real-time PCR showed that the expression of ER and AR m RNA were detected in four kinds of tissues,and extremely high in gonad.The expression of ER and AR in head kidney and intestine were higher than liver in male fish.The expression of ER m RNA of liver and gonad in female fish was higher than in male.And the expression of ER of intestine and head kidney in female fish was not different from male fish.The expression of AR of gonad and intestine in male fish was higher than in female fish.We can come to the conclusion that ER had different physiological effects on male and female fish.Similarly,AR had different physiological effects on male and female fish.