Growth And Gonadal Development Of Male And Female Pseudobagrus Ussuriensis And The Influence Of Its Early Growth And Gonads With Aromatase Inhibitor Treatment

Pseudobagrus ussuriensis is a kind of economic fish in freshwater which distributein Heilongjiang River and the Tai lake, it become a important breeding variety in recentyears because of the high economic value. Pseudobagrus ussuriensis reachs its sexualmaturity in three years, and gets spawning period from the middle of June to early July.Artificial breeding of Pseudobagrus ussuriensis mostly takes artificial ovulation andinsemination in June to reproduce. Aromatase is a key enzyme in the action of androgentransforming into estrogen, and then influence the sex of the animal and thereproductive activities. Our reseach observed the seasonal change of Pseudobagrusussuriensis’s reproductive physiology; studied on the reproductive physiologicalinfluence of aromatase from the angle of the histology; and cloned the sequence ofPseudobagrus ussuriensis brain aromatase gene cyp19b. The main results were shownas follows:1. Through the observation of growth process, previous research found that femaleand male Pseudobagrus ussuriensis had a notable difference in growth speed. Male andfemale has significantly weight difference in4months old and length difference in1year old. In November,3years old male Pseudobagrus ussuriensis’s weight is235.2%of females, in the same time, the length is150.3%of females. Curve fit the weight andlength then got the formula of the female and male fish, which were W=0.1825L^1.9646（R²=0.9445） and W=0.1881L^2.005（R²=0.9618）, both male and female fish are allometry.Pseudobagrus ussuriensis has seasonal fluctuation of growth speed,1year old fishgrow faster in summer and2years old one grow faster before its first sexual maturity.2. The gonad development was observed and compared with seasonal changes ofsex steroids level. Our result showed that the relative fatness kept going down fromDecember（2years old fish） to next October（3years old fish）, the level of17β-estradiol（E₂） and testosterone（T） in female Pseudobagrus ussuriensis both reached the peakvalues in May, which were （1624.23±331.4）pg/ml and （1320.85±279.12）pg/ml; themale’s also reached the highest E₂level[（323.17±147.36）pg/ml] in May, but it had the highest T level[（758.33±100.47）pg/ml] in April. After observating of the gonad, wefound the gonad developed at the third period in December and at the fifth period inJune, which indicated that gonadal development was synchronized with gonad maturityin both male and female fish.3. After the feeding test with different letrozole concentration, the results show:aromatase inhibitor （letrozole） do not promote the growth of Pseudobagrus ussuriensis.It can not improve testosterone （T）’s content when inhibiting estrogen synthesis.Letrozole can inhibit the aromatase expression thus influence the gonadal development.There is considerable influence in survival rate of female fish among three AI groups, itcan lead to irregular arrangement and underdevelopement of oocyte in ovary. Byultrastructural study of oocyte, we can find swollen mitochondria and wrinkle of nuclearmembrane. The influence in survival rate of male fish is considerable in both AI300andT groups. After observing of kidney tissues, some cavitys and partial hyperemia can befound.4. Using the technology of RACE, we cloned Pseudobagrus ussuriensis brainaromatase gene cyp19b cDNA complete cds, the cDNA was2119bp with106bp5’ UTR,510bp3’ UTR and1503bp ORF, which encodes535amino acids. The cds includes theâ… -helix,an aromatase specific conserved region â…¡and the heme-binding region â…¢.This sequence shares87.69%part with Pelteobagrus fulvidraco brain aromatases gene.