| Production and research experiments have shown that the male and the female of Siniperca chuatsi have different growth at the different stages.Therefore,mono-sex culture may have potential application prospect.In this paper,the development of gonad of Siniperca chuatsi from 0 to 60 days old was studied by histological section.AFLP molecular markers were used to screen the fragments of sex difference between male and female fish to search for sex-specific markers,the growth characteristics of the male and the female fish at the age of 0.5-4.0 months after hatching were compared,the serum levels of testosterone(T)and estradiol(E2)were measured by enzyme-linked immunosorbent assay(ELISA),and the expression differences of GH / IGF growth axis related genes in brain,liver and muscle tissues were quantitatively analyzed by real-time fluorescence,which provide basic data for the development of the gonadal development,sex molecular identification and the mechanism of growth difference between males and females of Siniperca chuatsi.The main results were as follows:(1)Gonadal development at early stageAt the age of 15 days,primordial gonads were observed,and gonads did not differentiate.At the age of 20 days,primordial germ cells began to proliferate.At the age of 25 days,the primordial germ cells proliferated in large numbers.At the age of 30 days,the gonads(testis)were leptonema,and the primitive germ cells began to differentiate into spermatogonium.Spermatogenic nuclei were larger and stained deeper.At the age of 35 days,the testis formed a saclike structure with several spermatogonia.At the age of 40 days,spermatogonia distributed in clusters and the seminiferous lobules formed.At the age of 45 days,spermatogonia began to differentiate into primary spermatocytes.At the age of 50 days,there were a lot of primary spermatocytes in the testis.At the age of 55 days,multiple seminiferous lobules were formed in the testis,containing clusters of primary spermatocytes.At the age of 60 days,there were a few secondary spermatocytes in the testis,and a lobular cavity was formed in the seminiferous lobule.Before 40 days of age,ovary had not yet differentiated.At the age of 40 days,the primordial germ cells differentiated into oocytes.At the age of 50 days,oocytes distributed around the edge of gonad,the volume of ovarian increased,the lacunae wrapped to form the ovarian cavity,and some of the oocytes differentiated into primary oocytes.At the age of 55 days,primary oocytes were irregularly distributed in the ovary.At the age of 60 days,the volume of ovarian increased further,the number of primary oocytes increased,the nucleolus was distributed along the nuclear membrane,and there was a layer of follicular cells on the outside.The results showed that the differentiation and development of the testis was earlier than that of the ovaries of Siniperca chuatsi.(2)Screening of sex related molecular markers in female and male fishFive sex-different loci were selected from four primer combinations E5M8,E1M8,E6M7 and E7M3 through the AFLP molecular markers technique of the males and the females of Siniperca chuatsi.Among them,the amplification ratio of E5M8-480 locus in males was 91.67%,the proportions of E1M8-440 and E5M8-370 locus in females were 91.67% and 83.33% respectively,and E6M7-280 and E7M3-380 locus were female-specific bands.After blast comparison,no sex determination gene sequences were found.It is necessary to increase the screening of specific marker sites for the gender of Siniperca chuatsi in future.Meanwhile,the occurrence of these sex difference bands may also indicate that the gender formation of Siniperca chuatsi is not caused by simple differences in gene locus,and its genetic determining mechanism may be more complex.(3)Differences of growth characteristics,sex steroid hormone content and gene expression level of GH/IGF growth axis between the male and the femaleUnder the same aquaculture conditions,the average body weight of the males and the females of Siniperca chuatsi at the 4.0 month age was 396.52 ±74.81 g and 442.17± 54.02 g,respectively.The growth rate of females was 10.32% faster than males.The ratio of head length to head height of the males was significantly higher than the females.The ratio of length to height of females was remarkably significantly higher than males and the ratio of body weight to body length was significantly higher than that males.Logistic growth equation of the weight and total length of the female and the male could be expressed as W(?)=6.67.57/(1+e^(4.19-1.24*t)),W(?)=582.71/(1+e^(4.07-1.27*t));L(?)=31.47/(1+e^1.95-1.08*t)),L(?)=26.20/(1+e^(2.56-1.5*t)).The inflection point for the weight growth of was 3.37 month in the female and 3.20 month in the male,the corresponding weight was 333.79 g and 291.36 g respectively,and the inflection point of total length growth was 1.80 month in the female and 1.70 month in the male.At the age of 3.0 month,the weight of the female was significantly higher than that of the male(P<0.05),the E2 content of the female was significantly higher than that of the male,the T content of the male was significantly higher than that of the female(P<0.05);the expression levels of GH,IGF ?,IGF ? in brain,IGF ? in liver and GH in muscle of the female were significantly higher than that of the male(P<0.05).At the age of 4.0 month,the weight of the female was remarkably significantly higher than that of the male(P<0.01),the content of E2 in the female was remarkably significantly higher than that in the male(P<0.01),the content of T in the male was significantly higher than that in the female(P<0.05),the content of E2 in the male decreased;and the expression levels of GH,IGF ? and IGF ? in brain and liver,GH and IGF ? in muscle of the female were remarkably significantly higher than that in the male(P<0.01).The results showed that the growth of the female was faster than that of the male Siniperca chuatsi in the later stage,and the growth difference might be caused by the relative level of E2 and T,which further regulating the expression level of GH/IGF growth axis genes. |
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