Occurrence and significance of ovarian and follicular regression in cachara Pseudoplatystoma fasciatum (Linnaeus, 1766): a histology approach

Abstract

The processes of ovarian regression and follicular atresia which reproduction was not induced by hormone in confined cachara, Pseudoplatystoma fasciatum, were investigated. The macro and microscopic characteristics (oocytes diameter and histology) of the ovaries were described every 20 days, in four stages: initial regression (Rg I = first 20 days), intermediate regression (Rg II = from 21st to 40th day), final regression (Rg III = from 41st to 80th day) and the recovering stage, called resting II (R II = from 81st to 150th day). The experiment was conducted from late January (summer - longer days) to May (autumn - shorter days). In the beginning, A0 samples showed oocyte diameters ranging from 437.5 to 1,187.5mm, suggesting that oocytes were in perinucleolar, at final maturation and atretic phases. After 150 days, the diameters reached the lowest values and a ruptured zona radiata, as well as the nearly complete reabsorption of the yolk could be visualized. At the same time, a sharp decrease in the mean values of the gonadosomatic index (GSI), water temperature, photophase and rainfall was observed. The gradual involution of this long process was dynamic and complex, affecting the spawning success (fertilization, eclosion and larvae survival rates) and, consequently, the whole productive system.