Studies On The Sex Reversal Regulation Of Monopterus Albus (Zuiew)

The rice field eel(Monopterus albus) can be found in China,India,Malaysia and Indonesia,and has been popularly cage cultured in central and southern China.The total output of China has reached 180,000 tons.It was a popular and highly appreciated fish on the Chinese market,and it has been selected as a target species for Chinese aquaculture due to its rapid growth,good survival rate and easy adaptation to cage culture conditions.However,Chinese rice field eel aquaculture was still at an elementary stage.Farming activities still rely on the capture of wild juveniles.With the increased fishing,the wild juvenile resources declined sharply.The achievement of controlled reproduction techniques of this species remains an essential prerequisite for domestication and development of farming activities for rice field eel.However,it has a special phenomenon of sex reversal:It was a hermaphroditical fish,early stages of development of life were females.After spawning,it became intersex,then entered male stage.The mainly spawning period was from May to June.When body length reached 35-45cm,it began to change its sex.Because of sex reversal,individuals of female were smaller. Absolutely fecundity was lower.Large-scale artificial breeding has not solved,therefore, the study of sex reversal played a very important role in solving the artificial breeding of the fish.The present study aimed to find the way of the manual control technology of sex reversal in M.albus,by using nutrition,exogenous hormone and environmental factors. The study could bring new breakthrough in breeding and promote the sustainable development of aquaculture industry. 1.The studies on the relations of body length,weight,age and sex ratio and fecundity in M.albusDuring 12 months,samples were collected in Diao-cha lake,Hubei province.The total number was 258.The number of females was 152(accounted for 58.91%),intersexes 44 (17.05%),males 62(24.04%).Total body length was 9.4-76.8 cm.Body length of female was 9.4-60.5 cm,average 39.6 cm.Those below 20cm were all females.Intersexual body length was 27.1-63.3 cm, average 44.5 cm.Body length of male was 29.4-76.8 cm,average 51.63 cm.Those 70 cm above were all males.The results show that 25 cm was the starting point of body length of sex reversal in M.albus.Total body weight was 0.48-753.60 g.The average weight of females was 58.46 g. Those below 23.70g were all females.Intersexual body weight was 25.40 g-206.30g, average 76.45 g.The weight of males was 29.65-753.60g,average 144.38 g.Those 250 g above were all males.The results show that 25 g was the starting point of body weight of sex reversal in M.albus.The number of females below 2 years accounted for 92.17%of the total females. Intersexual individuals were 2-5 years,and 3-4 years were the peak period.Males were 2-7 years.The number of males,2 years,only accounted for 2.00%of the total males. Those above 6 years were all males.The results show that 2 years was the starting point of the age of sex reversal in M.albus.The number of impregnated eggs was 41-1267.Those 20-30 cm had the highest impregnated rate.2.Effects of different protein level diets on sex reversal of M.albusThe study was conducted to investigate the effect of different protein levels(25%, 35%,45%and 55%) on sex reversal of M.albus.The study indicated that the gonadal development of M.albus was closely related with the protein levels in diets.In a short period(one month),the GSI of different groups was not significantly different.In the end of June next year,the GSI was significantly different.They were 1.45±1.05%,3.00±2.36%,7.71±1.67%,2.35±0.81%,respectively.GSI was closely related with the protein levels in diets.Within the appropriate context,the absolute intensity was increased with the protein levels in diets.The ratios of sex reversal individuals in different groups were different.25%protein levels groups,38.65±1.34%changed its sex to male,and 17.61±1.47%to intersex. 35%protein levels groups,24.15±6.55%changed its sex to male,and 11.20±1.45%to intersex.45%protein levels groups,7.61±1.43%changed its sex to male,5.21±1.25% to intersex,and 87.18±1.21%maintain female.55%protein level groups,14.21±5.52%changed its sex to male,about 7.18±0.96%to intersex,and the ratio of female in the groups was less than that of 45%groups.The study indicated that 45%protein level in diets could be favorable for gonadal development of female M.albus.In the studies on section of serum estradiol(E₂),E₂ of 45%protein level groups was the highest.E₂ of 35%and 45%groups were significantly higher than that of 25%,55% groups in April,May and June,and reached their peak value in June.The study indicated that it high section of serum E₂ could be maintained with the suitable protein levels in diets.It could delay the sex reversal of M.albus in some degree.3.Effects of different lipid level diets on sex reversal of M.albusThe experiment was conducted to investigate the effect of different lipid levels(5%, 10%and 15%) on sex reversal of M.albus.The study indicated that the ratio of sex reversal of M.albus was increased with fat level in the same protein level diets.5%fat level in diets could be favorable for gonadal development of female M.albus and increase the absolute intensity.4.Effects of different concentrations of exogenous testosterone propionate (TP) diets on sex reversal of M.albusThe study aimed to investigate the effect of different dose of TP(0 mg / kg,10mg / kg and 30 mg / kg) on sex reversal of M.albus.18.51%individuals in 30 mg / kg groups changed its sex to male,higher than that of 0 mg / kg and 10mg / kg groups,but the total ratio of male and intersual was no significant difference.The study indicated that different dose of TP has no significantly effects on sex reversal of the fish. 5.Effects of different concentrations of exogenous estradiol valerate diets on sex reversal of M.albusFishes were treated with different concentrations of estradiol valerate in diets,0mg/kg, 10mg/kg and 50mg/kg,for 12 months.Lower concentrations(10mg/kg) of estrsdiol valerate in diets could inhibit the sex reversal of the rice-field eel in some degree.Higher concentration of estradiol valerate in diets could reduce the secretion of T while the concentration of serum E₂ kept higher levels.The sex steroid hormonal profiles and experimental data lead to the conclusion that treatment of diets of estradiol valerate (50mg/kg) could delay the process of sex reversal in rice-field eel.6.Effects of different concentrations of exogenous Compound norethindrone diets on sex reversal of M.albusThe study aimed to investigate the effect of different dose of compound norethindrone (0 piece/kg,10 pieces/kg and 30 pieces/kg) on sex reversal of M.albus.The study indicated that treatment of diets of compound norethindrone could delay the process of sex reversal in rice-field eel.It has no significantly effects on body-length and body-weight of the fish.7.Effects of Eco-environmental stress(no habitat nest) on the sex reversal of M.albusThe E₂ levels without habitat nest groups were declined sharply in the first month.It reached peak value(618.18±30.05pg/ml) in April of the next year and significantly higher than that of controls.This study showed that environmental stress-no nest habitat could significantly affect the secretion of serum E₂ of M.albus.T levels without habitat nest groups reached its peak value(6.75±0.85 ng/ml) in May of the next year while controls reached its peak value(5.25±0.31 ng/ml) in June of the next year.The study indicated that no habitat nest could significantly affect the T secretion.Besides,the study showed that environmental stress-no habitat nest can significantly affect the growth of body-length,weight and the sex reversal of M.albus.After 12 months,38.85±0.85%individuals of the group without habitat nest changed their sex to male,47.14±3.50%maintained female.24.6±1.37%of the controls changed their sex to male,61.18±2.31%maintained female.It was confirmed that the starting time of sex reversal in the fish was at stageâ…£through more than 1,000 biopsy of gonadal tissue.The original spermatogonia hidden in female gonads gradually began to develop a small testis capsule and spread in the gap among oocytes.Then oocytes from the stageâ…£gradually developed intoâ…¤.Oocytes degenerated after spawning.Spermatogenic cells developed into primary spermatocytes and reproductive capsule could be seen with oocytes ofâ…¡,â…¢stages.With the development of male reproductive cells,oocytes degradated and started the male developmental stage.The phenomenon that eggs with yolk(â…£stage) and mature sperm cells co-existence in gonads was first found in fish.