Ovarian follicle growth in the catfish Iheringichthys labrosus (Siluriformes: Pimelodidae)

The morphofunctional organisation of the female reproductive system, the oocyte growth and the follicular envelope ultrastructure were studied by the first time in the catfish Iheringichthys labrosus from Upper Paraná River basin, Southeastern Brazil, in order to contribute to the knowledge of the reproductive behaviour strategies of this species. As in other Neotropical freshwater siluriforms, the ovaries are of the cystovarian type, the oocytes develop in an asynchronous pattern and mature oocytes are released in clusters in the ovarian lumen, being transported through the oviduct to the urogenital papilla. During the primary growth, nuclear material is transported to the ooplasm, forming the yolk nucleus, where proliferate membranous organelles. The onset of the zona radiata formation occurs during the late perionucleolar stage with the deposition of the outer layer. At the vitellogenic stage, this envelope reaches 6.35 ± 0.84 μm of thickness, being constituted by three distinct layers crossed by pore-canals containing oocyte and follicular cells processes. Cytochemical analyses evidence neutral glycoproteins in cortical alveoli, yolk globules and zona radiata. Follicular cells with squamous shape during the primary growth acquire synthetic activity at the secondary growth, reaching 37.82 ± 4.72 μm in height at the mature vitellogenic follicles. These cells accumulate sulphated polysaccharides in large electron-lucent vesicles during the vitellogenic stage which are possibly secreted to form a mucous coat at the egg surface. These evidences suggest that I. labrosus may have adhesive eggs as also detected in other Neotropical freshwater Siluriformes.