Ultrastructural and morphometric analysis of gametes in neotropical teleost fishes

Abstract

This study was designed to identify and measure the gametes of neotropical fish using ultrastructural analysis. Number, shape and size of micropyle and ultrastructure of egg membrane and of the micropyle canal; the number and length of the longest and shortest ridge in the micropyle region beyond the structures of the sperm cell have been used as taxonomic tool in ichthyology . Gametes of six breeding pairs of Piaractus mesopotamicus, Brycon orbignyanus, Salminus brasiliensis and Prochilodus lineatus were collected, fixed and subjected to scanning electron microscopy for the observation and measurement of the structures. The results showed many similarities between the gametes of the studied species. An array of grooves and folds was observed in the micropyle in all species but not in the Prochilodus lineatus oocytes. The micropyle was funnel-shaped in all species. The oocytes showed a great variation in the diameters of major and minor micropyle ostium, evidencing different reproductive strategies. The sperm cells showed simple structures with ovoide heads, a cylindrical midpiece with a single flagellum and no acrosome. This study may contribute to a better understanding of fish reproductive biology, conservation genetics and breeding studies.