Dynamics and cytochemistry of oogenesis in Leporinus striatus Kner (Teleostei, Characiformes, Anostomidae) from the Rio Sapucaí, Minas Gerais State, Brazil

Abstract

Irani Quagio-Grassiotto 4 AB STRACT. Oogenes is in volves a sequense of transformati ons whi ch are undergo ne by female germ cell s. These cells change into oogonias and then into mature oocytes. Sexually matu re fe males were collected monthly, during one year, from the Rio Sapucai, tri butary of the Ri o Grande, which is part of the Furnas Reservo ir system in the state of Minas Gerais. The observed material showed that oogoni as were small spheri cal cells, had a big spherical nucleus, with a single nucleolus, and weakly stained cytoplasm with eos inophili c granules (FG stained), which indi cate their protein content. T he primary oocytes showed a big basophilic nucleus, with a large peripheral nucleo lus, and several smaller nucleoli . They show a redu ced cytopl as mic content. The previtellogenic oocytes presented voluminous cytoplas m and nucle us w ith everal small peri pheral nucleoli . Theoocytes underwent vitell ogenes is with the development of the zo na radiata and the fo llicle cells. The zona radi ata had two layers, the outer and the inner, whi ch showed its protein content when stained with CM and FG techniques. TB pH 2. 5 and pH 4.0 staining showed that oocytes undergoing vitell ogenesis presented weakly stained cy toplasm and peri pheral cytoplas mi c vesicles. The follicle cell s that were squamous became cuboidal. In mature oocytes, the yolk granules that fi lled the cytoplasm became green and blue when stained with FG and CM techniques, indi cating their protein content. The peri vitelline reg ion showed rosy stained ves icl es (TB pH 2.5 and pH 4.0) spread among the weakl y stained peripheral vesicles, whi ch seemed to be the cortical alveoli . The zona radiata cell s, CM and FG stained, still showed two layers like the oocytes from the previous stage, but thicker. KEY WO RDS . Teleostei, Anostomidae, Lep orinus stria/us, oogenesis, cytochemi cal Anostomidae are herbivorous fi shes , of small and medium size, very appreciated as fo od and in game fishing (BRITSKI 1972), and usuall y found in neotropical rivers . Small size species, such as Leporinus striatus Kner, 1859, are al so found in reservoi rs, where they form the bas is of the food chain ( NOM URA 1984).