Histological study on the gonadal development of Scatophagus argus

Abstract

The fish spotted scat Scatophagus argus,as a new resource of marine aquaculture,is popularized in South China in recent years.Studies on the gonadal development can provide the theoretical knowledge for the artificial propagation of Scatophagus argus.Generally,after two years of growth,some individuals can reach sexual maturation in the south of China.In this study,histological observation of gonads was performed based on paraffin section technique and HE staining method.The linear alignments of tubular structures are observed in the testis,which indicates that the testis of the Scatophagus argus belongs to the tubular type.The development of testis may be divided into 5 stages,i.e.multiplication of spermatogonial cells,growth of spermatocytes,maturation of spermatocytes,emergence of spermatoblasts,maturation of spermatozoa,etc.The average gonado somatic index of the testis was between 0.2% and 1.5%.The gonado somatic index(GSI)reached the peak at the stageⅤ,and the the peak of hepato somatic index(HSI)was observed at the stage Ⅳ.The oocyte deveolpment was divided into 5 phases and ovary development consisted of 5 stages accordingly.The average gonado somatic index of the testis was between 1.2% and 14.5%.The gonado somatic index(GSI)reached the peak value at the stage Ⅴ and the peak of hepato somatic index(HSI)was found in stage Ⅳ.The yolk nucleus and follicle membrane are observed at phase Ⅱ of oocyte.The number of yolk granules and oil droplets increased rapidly at the phaseⅢ,and subsequently yolk granules fused into pieces at the phase Ⅳ Apart from a large number of oocytes at the phase Ⅴ,there are still many oocytes of phase Ⅱ,Ⅲ and Ⅳ in ovaries at the stage Ⅴ.The similar condition was also found in ovaries after spawning.It indicates that oocyte development in Scatophagus argus is asynchronous.