Morphogenesis of Olfactory Organ of Bushymouth Catfish Ancistrus dolichopterus (Teleostei: Loricariidae) before Switching to Exogenous Feeding.

Olfaction plays an important role in a fish's life. Its value may differ at different developmental stages, depending on the feeding style of the species. The goal of the present study was to investigate the olfactory organ of a species that feeds mainly on algae- the bushymouth catfish, Ancistrus dolichopterus-at developmental stages from olfactory placode to the definitive olfactory chamber. For this study, we used light and electron (scanning) microscopy. The topography of the olfactory placode of A. dolichopterus is typical for teleostei. Formation of olfactory pit takes place at the same time as rostral elevation formation. Rostral elevation participates in the formation of the nasal bridge and anterior tubular nostril. It was found out that the anlage of olfactory rosette in A. dolichopterus arises earlier than in most teleostei. However, the number of lamellae does not increase until switching to exogenous feeding. We suppose that the early development of olfactory organ is necessary for intraspecific communication, not just for finding food.

Light Microscopy of Development of the Olfactory Organ of European Weatherfish Misgurnus fossilis (Тeleostei: Cobitidae).

We studied the formation of the olfactory organ of European weatherfish Misgurnus fossilis (Linnaeus, 1758) from the formation of its placodes to the formation of lamellae using light microscopy. The aim of the present investigation was to determine which morphogenetic features of the olfactory organ ate associated with the demersal lifestyle. The olfactory organ of European weatherfish goes through such developmental stages as olfactory placode, olfactory pit, and olfactory chamber with lamellae. Formation of the olfactory pit occurs in prolarvae, but a considerable increase in size takes place during the switch to exogenous feeding. In late larva, lamellae are formed in the aboral part olfactory chamber as an outward fold at its bottom. At the same time, incurrent and excurrent nostrils start being formed as the result of approximation of lateral and medial margins in the rostal part above the olfactory cavity. In contrast to other fishes, the peculiarity of morphogenesis of olfactory organ of M. fossilis is its late formation followed by intensive postembryonic development.