REPRODUCTIVE CYCLE, GAMETOGENESIS AND EMBRYONIC DEVELOPMENT OF NITIA TERETIUSCULA (BIVALIVA: UNIONIDAE), FROM THE RIVER NILE, AT SOHAG GOVERNORATE, EGYPT

The present study dealt with the description of the reproductive and gametogenic cycles and the embryonic development of the freshwater mussel Nitia teretiuscula from the River Nile. Macro and micro-anatomy showed that the present species is dioceous and gonadosomatic indices showed that the species is semiannual and had two gonadal growth periods, a short period of gonadal growth from January to March and a long period from April to August. Visceral indices revealed a reciprocal relationship with the gonadosomatic indices of both the two sexes. The recorded sex ratio of females to males was (1.5: 1). The oogenesis displayed five developmental stages; oogonia, previtellogenic oocytes, vitellogenic oocytes, late vitellogenic oocytes and mature ova. Also, spermatogenesis illustrated five developmental stages: spermatogonia, primary spermatocytes, and secondary spermatocytes, spermatids; which clustered to form sperm morula and finally metamorphosed to spermatozoa. Within the gills of females (marsupia), brooding of embryos was occurred till the formation of glochidia larvae. The unfertilized eggs were released from the gonads with distinct germinal vesicle. The fertilized eggs had two polar bodies and a fertilization cone. Successive cleavages were observed. Spiral cleavage, non-ciliated blastula and D-shaped larvae were recorded.