Influence of cortisol along the pituitary-ovary axis in the cichlid fish Oreochromis mossambicus

Abstract

Cortisol is the principal glucocorticoid released due to various forms of environmental as well as aquacultural stressors in fish. The aim of the present investigation was to determine cortisol-induced alterations along the luteinizing hormone (LH)-secreting cells–ovary axis in the tilapia Oreochromis mossambicus. Administration of cortisol to stripped O. mossambicus for a period of 22 days during the ovarian cycle caused significantly higher number of follicles with chromatin nucleoli (stage I) compared to those of initial controls and controls. Whereas the number of follicles at perinucleolar (stage II) and vitellogenic (stage IV) stages did not differ significantly between controls and cortisol-treated fish, the number of follicles at cortical alveolar stage (stage III) was significantly lower in cortisol-treated fish than in controls. While the stage V follicles (maturation stage) were absent in initial controls, their presence in controls was concomitant with intensely labelled LH-secreting cells in the proximal pars distalis (PPD) region of the pituitary gland during prespawning phase. However, cortisol-treatment resulted in complete absence of stage V follicles associated with weakly immunoreactive LH-content in the PPD region of the pituitary gland during prespawning phase. These results suggest that chronic cortisol- treatment causes suppression of LH-secreting cells activity and blocks progression of vitellogenic follicular development process in O. mossambicus.