COMPARATIVE ONTOGENY AND CYTOMORPHOLOGY OF THE NASAL ORGANS IN SOME SPECIES OF CICHLID FISH (CICHLIDAE, TELEOSTEI)

This study compares the ontogenesis, morphology and cytology of olfact ory organs of several species of Cichlidae (Pisces, Teleostei), from A sia, Africa and America, belonging to the subfamilies Tilapinae and Ha plochrominae. Cichlids, in contrast to most other fish families, posse ss only one naris on each side of the nose that serves as both inlet a nd outlet opening. The olfactory rosettes are round, 1.8-4.2 mm diamet er, and situated directly below the nares. Each rosette consists of a central raphe with attached lamellae whose number increases with age, remains constant in adults and differs in the various species. Onset o f organization of the nasal organs from the neuroectoderm begins 14-16 hours after fertilization in bottomspawner cichlids, and 30-53 hours after fertilization in mouthbrooder embryos. A comparative ontogenetic study of embryos and larvae of both ethological types has shown that this difference in timing of morphogenesis also continues in the forma tion of the nasal pits, the development of the nasal epithelium, and t he olfactory nerves. Comparative data are provided for these processes , including LM, TEM and SEM of the stereocilia and kinocilia-bearing c ells, as well as of the microvillar cells. The distribution of these c ell-types on the olfactory lamellae differs in the various species. Th e faster development of the nasal organs observed in larvae of bottoms pawners as compared to mouthbrooders also matches the development of o ther vital organs in these two etho-types and seems to be of high adap tive value, providing the bottomspawners at an earlier stage with sens itive organs in the surrounding hostile habitats.