Effect of water temperature on gonadal development in half-smooth tongue-sole (Cynoglossus semilaevis Günther)

Although females grow 4-6 times faster and reach larger adult sizes than males in half-smooth tongue-sole,Cynoglossus semilaevis,male ratio is higher than female study culture conditions.Thus,it is necessary for us to make a detailed understanding of gonadal development,which provides a theoretical basis for sex control.What's more,water temperature is considered a very important modulator of reproductive activity in fish.Therefore,the principal purpose of the present work is to analyze the effects of different temperatures(19,21,23,25 and 27 ℃)on gonadal development in the half-smooth tongue-sole,which were reared for 67 days from 39 to 106 days post fertilization(pfd).And the temporal dynamics of germ cell growth and gonad development were examined during the experiment using light microscopy method.We found that the histological differentiation occurred firstly on pfd46 in the half-smooth tongue-sole reared at 19 ℃,as the gonad with the increasing primordial germ cells(PGCs)will develop into ovary.And the gonad without cavity will develop into testis in fish held at 19 ℃ on pfd82.At the same time,compared with fish kept at other temperatures,half-smooth tongue-soles maintained at 27 ℃ demonstrated increased oogonium proliferation in females and the spermatocyst size in males.And the ovaries of the fish reared at 27 ℃ were in stage Ⅱ on pfd129.Higher water temperatures triggered rapid germ cell differentiation and seminal vesicle growth,and relatively,lower water temperatures delayed,hence,not until pfd142,the ovaries of juvenile feeding at 23 ℃ and 25 ℃ were in stageⅡ.In addition,under higher temperature treatment,there were more oocytes in the ovarian lamella;in males,late-stage testis germ cells were predominated at this time,Especially in the juveniles rearing at 25 ℃,spermatozoa were distributed to almost all seminal lobules,even seminal vesicles and sperm ducts were filled with high density spermatozoa.All of these results suggest that higher water temperature favors gonadal development.