Effects Of Temperature On Early Growth And Sex Differentiation In Little Yellow Croaker

Fish is a kind of temperature-changing animal whose body temperature will change with the temperature of the cultured water.Therefore,water temperature has a close influence on the growth,development,reproduction,activity and foraging of fish.Fish is also a kind of low vertebrate,genetic and environmental factors will work together to influence its sex and differentiation.In this study,5 temperature treatments(16,22,28,34℃,nwt(natural water temperature))were designed for evaluating the different temperature effects on early growth stage of 10 days after hatching(10 dah)of little yellow croaker.By comparing the growth index,gonad differentiation rule,sex steroid hormone level and expression of genes related to sex determination in each group,then ascertain the effects of temperature on early growth and sex differentiation of little yellow croaker.The results shown that:1.The little yellow croaker cultured under low temperature 16 has a poor growth and ℃low survival rate of 16%.32.4±0.5 ℃was the initial lethal temperature and 34 ℃was lethal temperature for little yellow croaker.22 ℃group in the early heating stage showed growth advantage over the nwt group,but the total length and body weight had no significant difference(P>0.05)compared with the ntw group after 90 dah.28±0.5 is the suitable growth ℃temperature for little yellow croaker,after 90 dah,the average total weight and length had significant difference with the nwt group(P<0.05).The growth rate of little yellow croaker was relative fast during the last twenty days.2.The ovary develops earlier than the testis of little yellow croaker in each group,and the ovary develops about 40 days earlier than the testis in nwt group.The gonadal differentiation rate of the little yellow croaker in the high temperature group(28℃,28℃↑)was 10-15 days faster than that in the nwt group and 40 days faster than that in the 16℃ group.Ovary development of little yellow croaker is continuous,but the testis exists the hermaphroditic ovarian stage in 60-80 dah.The sex ratio of females to males in the 22℃ and nwt groups was approximately 1:1,and the proportion of females in the 28℃ and 16℃ groups was greater than that in the other groups,continued high temperatures can increase the female rate.The E2(estrogen)content was higher than the 11-KT(androgen)of little yellow croaker in 90 dah,but the temperature had no significant effect on the 11-KT content.High temperature could significantly increase the E2 content in females but couldn’t significantly affect the E2 content in males.3.There are two aromatase genes named cyp19a1 a and cyp19a1 b exit in little yellow croaker and have highly homology with large yellow croaker.cyp19a1 a expressed significantly higher than that in the testis of little yellow croaker in 90dah(P<0.05).cyp19a1 b expressed in the brain significantly higher than that in the gonads(P<0.05).The sf-1 of the little yellow croaker is highly homologous to zebrafish,and it is highly expressed in the testis in 90 dah,but the expression is higher in the 240 dah little yellow croaker brain.The expression levels of cyp19a1 a in the ovary of the 28℃ and 28℃ groups were significantly higher than that in the nwt group and the 16℃ group,but there was no significant difference between the temperature groups in the testis and brain(except for the 16℃group).The expression levels of cyp19a1 b in ovary,testis and brain were not significantly different in each temperature group,but the expression levels of sf-1 in the ovary,testis and brain of the 28℃ group were significantly higher than those in the other temperature groups.In summary,in the appropriate temperature range,high temperature has a significant role in promoting the early growth of little yellow croaker,and can speed up the rate of gonadal differentiation and cause a high proportion of females of little yellow croaker.This study can provide a theoretical basis for the rapid artificial breeding and understand the gonad development in the early stage of little yellow croaker,and discuss the mechanism of sexual differentiation of little yellow croakerat the same time.