THE SPERMATOGENETIC PROCESS IN BARBUS-LONGICEPS, CAPOETA-DAMASCINA AND THEIR NATURAL STERILE HYBRID (TELEOSTEI, CYPRINIDAE)

Testicular ultrastructure was studied in Barbus longiceps, Cupoeta dam ascina and their natural hybrid. The testes of these teleosts belong t o the unrestricted or lobular type. Germ cell morphology is similar in the parental males, In the hybrid, spermatogenesis does not extend be yond the pachytene of the first meiotic division. probably due to the unsuccessful pairing of the homologous chromosomes. Hybrid testes are occupied mainly by degenerating primary spermatocytes, at the leptoten e and pachytene stages. In both parents and the hybrid, Sertoli and Le ydig cells are characterized by the presence of granular endoplasmic r eticulum and of mitochondria with tubular cristae. Due to the arrest o f spermatogenesis, the male germ cell protective barrier is absent in the hybrid. Germ cell nuclear size was measured by a computerized anal ysis system, using light-microscopy images. In the parents and the hyb rid, germ cells attain a uniform inter-individual nuclear size when th ey reach the first meiotic prophase. The nuclear size of primary sperm atocytes is similar among the three groups of fish,possibly reflecting their close genetic relationship. (C) 1996 The Fisheries Society of t he British Isles