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The tilapia, Oreochromis mossambicus, shows a short ovarian cycle of 24-26 days in nonmouthbrooding condition. In this study, the stripped female O. mossambicus were exposed to repeated mild acute stressors such as handling, chasing, frequent netting and low water levels daily for a period of 26 days. The follicular dynamics did not show significant difference during previtellogenic phase (day 12), whereas the mean number of stage IV (vitellogenic) follicles remained significantly lower compared with controls at the end of vitellogenic phase (day 18). The stage V (vitellogenic, preovulatory) follicles were completely absent in contrast to their presence in controls prior to spawning (day 23). The control fish spawned spontaneously after 24 days and entered mouthbrooding phase, whereas those exposed to stressors did not spawn. Furthermore, the serum levels of estradiol (E(2)) remained significantly lower concomitant with a significant increase in the serum cortisol concentration during vitellogenic and prespawning phase compared with those of the controls. The LH cells in the PPD of the pituitary gland showed weak immunoreactivity through vitellogenic and prespawning phase in fish exposed to stressors indicating the diminished secretory activity in contrast to the intensely stained ir-material in controls. The study reveals the disruptive effects of aquacultural stressors on the spawning cycle through suppression of LH and E(2) secretion along the pituitary-ovary axis. The results suggest that the ovarian stress response depends on the phase of the cycle and that the interruption of the spawning cycle is due to inhibition of recruitment of preovulatory follicles in O. mossambicus.

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Stressors (handling, chasing, and noise) applied randomly five times per day for one month to lizards during the recrudescence phase of the ovarian cycle caused a significant reduction in mean number of oocytes and primordial follicles when compared to those of controls. Further, vitellogenic follicles were absent in the ovary of lizards subjected to stressors. Administration of bovine FSH during post-breeding regression phase of the ovarian cycle induced ovarian recrudescence as shown by significant increases in the mean number of oogonia, oocytes, and primordial follicles compared to controls, as well as vitellogenic growth of follicles. However, lizards treated with FSH and exposed to stressors did not exhibit ovarian recrudescence. Furthermore, FSH administration during the post-breeding regression phase caused a significant increase in serum levels of estradiol compared to controls, which was accompanied by significant increases in the relative weight of the liver and oviduct, as well as vitellogenic growth of follicles. Despite administration of FSH to lizards subjected to stressors, there was neither any increase in serum levels of estradiol and weight of the liver nor vitellogenic growth of follicles. The results indicate that repeated application of stressors inhibits vitellogenic growth of follicles by suppression of steroidogenic activity in M. carinata. This is the first report revealing that the ovary does not respond to gonadotrophin treatment under stressful conditions in reptiles.

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