The atretic structures in the gonads of the rice-field eel (Monopterus albus) during natural sex-reversal

The gonad of the protogynous, hermaphroditic teleost, Monopterus albus were examined histologically at monthly intervals throughout one year. In particular, the epithelium of the maturing follicles of the female and the atretic follicles in the female, intersex and male were studied. Atretic follicles were common in the gonads and were classified as corpora atretica types 1 to 5 according to histological criteria. In addition, other regressive structures were observed in the gonads of some males. The histology and the frequency of occurrence of the atretic structures in the three sexual phases is described and discussed.