| Environmental Endocrine Disrupting Chemicals（EDCs）are a class of exogenous chemicals,including estrogen-like substances,organochlorine pesticides,and heavy metals.EDCs affect the normal synthesis and metabolism of biological endocrine hormones,which in turn affects the stability of the biological internal environment,reproductive development,and other normal physiological activities.EDCs are widely found in water,atmosphere,soil,and other environments,with the highest concentration in the water environment.Biphenol A（BPA）is the highest concentration of environmental endocrine disruptor in coastal areas of China.It has estrogen-like effects.Studies have shown that BPA has toxic and lethal effects on fish,and can affect the growth and gonad development of fish.BPA was detected in all water samples from coastal areas of China in winter and summer.The average concentration of BPA was 0.449μg·L-1 in summer and 0.186μg·L-1 in winter.The concentration of BPA in the South China Sea could reach 1.4μg·L-1 in winter.The concentrations of BPA in Zhejiang coastal waters ranged from 0.3 to 1.0μg·L-1 in winter and from 0.02 to 0.4μg·L-1 in summer.As an important economic fish in China,the little yellow croaker is widely distributed in Chinese coastal waters.Previous studies revealed that the a male-specific transient hermaphroditic stage occurs in little yellow croakers during gonadal development,and studies have shown that this stage is mainly influenced by genetic factors,but environmental factors are not excluded.To investigate the acute toxicity of BPA,the semi-lethal and safe concentrations of little yellow croaker,the present study performed the acute toxicity test of juvenile little yellow croakers（25 days after hatching）for 96 hour（h）exposure with different concentrations of BPA in the range of 0～5.0 mg·L-1.The survival rate of little yellow croaker was counted for each group and period.The results showed that BPA was not detected in the cultured water by HPLC-MS（High Performance Liquid Chromatography-Mass Spectrometry）.After 96 h exposure of different concentrations of BPA,the survival rate in the range of 0～2.5 mg·L-1and ethanol control group was above 96.73%.When the concentration of BPA reached 3.0mg·L-1,the survival rate significantly decreased to 81.25%,and when the concentration reached 5.0 mg·L-1,the survival rate decreased to 0%.It was calculated that the semi-lethal concentration and safe concentration of little yellow croaker were 3.94 mg·L-1 and 1.08mg·L-1 respectively after 96 h of BPA exposure.To investigate the effects of BPA on the growth and gonad development of little yellow croaker,four concentrations of 0,0.001,0.050 and 0.5 mg·L-1 and the control group were set up to BPA exposure from 30 days post hatching（dph）for 60 days.After exposure,the fish were continued to be cultured normal until 150 dph.The results showed that the body length and body weight of little yellow croakers were not significantly affected by different concentrations of BPA for 30 dat（dat,days after treatment）,and the gonadal weight of females in 0.5 mg·L-1 exposure group was significantly lower than that in other exposure groups.The gonadal maturation coefficient of female yellow croak in 0.05 and 0.5 mg·L-1exposure groups was significantly lower than that in other exposure groups,and there were no significant differences in male gonadal weight and gonadal maturation coefficient among exposure groups.Histological observation showed that 0.001,0.05 and 0.5 mg·L-1 exposure groups had no significant effect on ovary compared with the control group,0.001 mg·L-1exposure group showed a large number of early oocytes to become ovotestis,0.05 and 0.5mg·L-1 exposure groups showed testicular cortical hyperplasia.The statistical results of the number of germ cells in each group showed that the number of germ cells in testis and ovaries of 0.5 mg·L-1 exposure group was significantly decreased,while there was no significant differences between other groups and control group.At 60 dat,compared with the control group,the body length and body weight decreased with the increasing of exposure concentration,and there was no significant differences in the female,but the growth of males was significantly inhibited.The gonad maturity coefficient of female was significantly lower in 0.05 and 0.5 mg·L-1exposure groups than other groups.The results of histological observation showed that the ovarian oocytes in 0.001,0.05 and 0.5 mg·L-1exposure groups degenerated apoptosis compared with the control group,and the apoptosis was more serious with the increase of exposure concentration.The testis oocytes in 0.001mg·L-1 exposure group were completely degenerated,and there was no significant differences in testis of the control group.The testis in 0.05 and 0.5 mg·L-1 exposure group demonstrated gonadal structure development disorder and the testicular cortical hyperplasia.The number of ovary germ cells in 0.05 and 0.5 mg·L-1exposure groups was significantly lower than that of control group,and the number of testis germ cells in 0.5 mg·L-1 exposure group was significantly lower than that in control group.The inhibition of BPA exposure on the growth of little yellow croaker was still not recovered after 150 days of normal feeding.The gonadal structure development disorder and apoptosis of oocytes in the ovary persist.The number of germ cells in all the ovaries exposure with BPA was lower than that of the control group,while the number of germ cells in the testes was lower only in the 0.05 and0.5 mg·L-1exposure groups.BPA did not cause feminization of little yellow croaker population after long term exposure from 30 dph.The results from this study showed that BPA has toxic effect on little yellow croaker,it’s belong to medium toxicity,long-term exposure can inhibit the growth of little yellow croaker.It leads to the apoptosis of oocytes in the ovary of little yellow croaker.Produce the ovotestis,testicular cortical hyperplasia and gonadal structure development disorder,reduce the number of germ cells in the gonads,And these effects are long-lasting and persist after the exposure is stopped.This study investigated the toxic effects of BPA on the growth and gonadal development of little yellow croaker.Provide data basis for the following study on the effects of BPA on gonadal development.Enriched the research results of BPA toxicity to marine organisms.These results provided the reference for studying the toxic effects of BPA on other organisms,and basic data for sex control theory of little yellow croaker.It has significance to protect the population resources and promote the industrialization of artificial cultivation of little yellow croaker. |
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