Involution of post-ovulatory follicles in Pseudoplatystoma fasciatum (Pisces, Teleostei)
Keywords:
fish, Pseudoplatystoma fasciatum, post-ovulatory follicle, spawningAbstract
Great importance is given nowadays to catfish rearing due to the knowledge generated by research so as by the enterprises created by the private sector. The objective of this study was to investigate the degeneration of the remaining post-ovulatory follicles (POF) and the nature of the reproductive behavior of Pseudoplatystoma fasciatum in captivity. Thirteen hours after the injection of the second hormonal dose, 24 females of the species, which had released their oocytes artificially, were sacrificed at different times - 0, 1, 3, 6, 12 and 24 hours, in the final of the reproductive periods: 12 females in January 2001 (1st ovarian maturation) and 12 in January 2002 (2nd ovarian maturation). After that, fragments of ovaries were processed for light microscopy observations. In those periods, the maximum mean values of water temperature (26.0 ± 1.0°C) and GSI are registered, thus showing that the females are ready for hormonal induction. At first (0 to 3 hours), it is observed hypertrophy of cells of the granulosa and theca. After 6 hours, a sharp reduction of the follicles, in comparison with the previous stage, as well as irregular projection of the granulosa and intense vascularization of the theca are verified. The cells of both layers are intermingled, penetrating more and more into the lumen. For the first time, chromo phobic follicular cells, yellow-brown pigments and apical cytoplasmic projections are detected inside the follicles. It is possible to observe that after 24 hours the post-ovulatory tissue is vacuolated, probably containing lysosomes, indicating the end of the degeneration process. In P. fasciatum, the rapidity of the process of POFs involution and degeneration may be attributed to the fact that the species performs total spawning and single, has short spawning period (two months), presents high fecundity, does not protect its offspring, and exhibits an intense proliferation of primary oocytes and countless oogonia.
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