Preliminary Studies On Gonadal Development And Serum Factors Related Of Cultured Chinese Sturgeon

Chinese sturgeon(Acipenser sinensis Gray) is one of the protected animals in China. It is an anadromous fish that spends most time of its life in the seas,and spawns in the rivers,mainly in the Yangtze River.Dramatic decline in the Yangtze River population was attributed to the dam construction,overfishing and water pollution.Thus,we need immediately develop conservation measures for the species.The stock enhancement of fish has been conducted since 1983.The cultured individuals have not been sexually,or close-cycle captive breeding has not been completed yet.The studies on the physiology and endocrinology of Chinese sturgeon are very important,which are important to the artificial propagation.â… investigated the gonads of cultured Chinese sturgeon.The plasma levels of the estradiol(E₂) and testosterone(T) in Chinese sturgeon during the development were measured by Radioimmunoassay(RIA).The plasma VTG was measured by an indirect method,measuring the alkali-labile phosphorus content of the lipid-free protein fraction.Andâ… had conducted a study on the 1 year-old sturgeons, which were cultured in different temperatures.The results are as follows:1.The oldest cultured Chinese sturgeons were 11 year-old(total length:177～225cm, body weight:45.5～84kg),which were born in 1997 by artificial propagation.Most of them were in the gonadal development stageâ…¡.The maximal oocyte diameter of the oldest female was about 500μm,however,most were from 100 to 400μm.There were one or two follicle velums around the oocytes.Most of the males were in the gonadal development stageâ…¡,some were in the stageâ…¢.Also one 10 years old male was found in the early stageâ…£,which had many blood vessels in the testis and all kinds of spermatocytes.2.â… measured the concentration of sex steroids in the serum of cultured Chinese sturgeon(from 1 to 11 years old ) and the matured wild ones by RIA.In the cultured fish,the E₂ level is ruleless,the high ages are lower.The level of females are higher than the males in the cultured fish at the same ages,however,the males are higher than the females in the wild ones,but there are no significant differences(P＞0.05).In the wild fish for artificial spawning fish,the E₂ levels are higher in prespawning than in postspawning period,with no significant differences(P＞0.05).In addition,the results also show that it is little in the overian succus of the spawning fish.Generally,the T level ascends with the ages.It declines from 1 year to 3 years (0.04±0.02 ng/ml),then ascends slowly.It was 1.32±0.81 ng/ml at 10 years,but they were lower than 1.0 ng/ml at other ages.The T level of the wild fish is high,which is extremely higher than cultured ones.It was 2.87±8.70ng/ml at the gonadal development stageâ…¢of wild fish,and 10.96±22.60 ng/ml at the matured.It is suggested that the T level ascends quickly after the development stageâ…¢,but changes a little before stageâ…¢.There are extremely significant differences(P＜0.01) between the cultured and the wild.That in the males is higher than that in the females in the cultured fish at same ages,however,reversed in the wild ones.In the artificial spawning fish,the T levels are higher in prespawning than in postspawning period,with no significant differences(P＞0.05).In addition,the results also show that it is higher in the overian succus than postspawning period of the spawning fish.3.The results show that the levels of plasma VTG are low at the early ages from 1 to 5 years,and then increase.It waves from 7 to 11years.The matured wild sturgeons had the highest levels of 52.0±4.5mg/L.From the gonadal development stageâ…¡to stageâ…¥,the VTG levels of females increase quickly especially during stageâ…¡to stageâ…¢,the highest level is at stageâ…¤,and descend at stageâ…¥.However,it increases slowly in males during stageâ…¡to stageâ…£.At stageâ…£,the level was 28.7±12.2mg/L in males.In the artificial spawning fish,the VTG levels are higher in prespawning than in postspawning period.It was 62.5±8.7mg/L in prespawning.In addition,the results also show that it is higher in the overian succus of the spawning stock than in the other ages.The levels of E₂,T and VTG are consistent in spawning fish.It is suggested that the cultured Chinese sturgeon in fresh water were likely to be matured.4.One year sturgeon which cultured at different temperatures was studied.The results show that the growth rates are different in early stages.The maximal specifical growth rate(SGR) of larva occurred at 19.24℃,the maximal SGR of fingerlings is at 21.17℃,and the juvenile is at 30.51℃.The correlation model of average total length of 1 year fish is 25℃(72.4cm)＞22℃(71.8cm)＞19℃(68.6cm),that of the average body weight is 25℃(1.88kg)＞22℃(1.83kg)＞19℃(1.55kg).It suggests that the growth of young Chinese sturgeon is positively correlated with the temperature.It is observed that 1 year fish are in the gonadal development stageâ… ,with the dividing genital cells.We also found the rate of gonadal development is faster in the high temperatures than in the low teams.We examined the sex by the light microscope.The sex ratios of the fingerlings from the eggs captured in the spawning ground below the Gezhouba Dam is 1.Under the experimental conditions,the sex ratios are different in different temperatures.The ratios at 19℃,22℃and 25℃are 2.17,1.31,and 1.18 respectively.It suggests that the sex ratio would be changed by temperature,the change is positive correlation with temperature.There is negative correlation between the E₂ levels and tempertures,19℃＞22℃＞25℃,with no significant differences(P＞0.05).There is positively correlated between the T levels and temperatures,19℃＜22℃＜25℃,with significant differences(P＜0.05) between 19℃and 22℃or 25℃,no significant differences between 22℃and 25℃.As for the VTG,the correlation model is 19℃＞25℃＞22℃,the character of significant differences analysis is consistent with T.It suggests that the levels of T and VTG are influenced greatly by temperature.There are no significant differences between males and females at the same temperature.