Effect of egg deprivation on sex steroids, gonadotropin, prolactin, and growth hormone profiles during the reproductive cycle of the mouthbrooding cichlid fish Oreochromis niloticus

Various hormones were analyzed during the course of a reproductive cycle in the cichlid fish Oreochromis niloticus: plasma levels of the gonadal stero ids 17 beta-estradiol (E2), testosterone (T), 17,20 beta-OH progesterone (1 7,20 beta; P), gonadotropin (taGtH), and plasma and pituitary concentration s of prolactin (tiPRL(I) and tiPRL(II)) and growth hormone (tiGH). Two cate gories of fish were sampled and sacrificed on days 1 and 3 postspawning and at 3-day intervals thereafter: typical incubating females (INC), and nonin cubating females (NI), deprived of their eggs just after spawning. Such dep rivation is known to suppress maternal behavior and to accelerate ovarian d evelopment and especially vitellogenesis, thus shortening the mean interspa wning interval. In both groups, variations of the plasma concentrations of E2 and T appeared to depend on ovarian stages, and differences between grou ps appeared to reflect underlying differences in the kinetics of ovarian de velopment. The observation of noticeable levels of 17,20 beta-P in plasma b efore spawning, when high values of taGtH could also be detected in NI fema les, suggests the implication of this progestin in the control of final mat uration events, as in some other teleosts. Moreover, 17,20 beta-P, which wa s still detected a few days after spawning, but at low concentrations and o nly in the plasma of INC females, might play a role at the beginning of the reproductive cycle in incubating females (maternal behavior and/or slowing down of ovarian growth). The pituitary and plasma profiles of both tiPRLs isoforms appeared to depend mainly on the kinetics of ovarian development i n each group of fish, suggesting a role during the beginning of vitellogene sis. However, the variance of plasma tiPRL(II), which was significantly enh anced during maternal behavior in INC females, also suggests an implication of this hormone in the control of that behavior. Concerning tiGH, comparis on of the plasma profiles in INC and NI fish also suggest an influence on t he control of maternal behavior, but a main effect of starvation of INC dur ing mouthbrooding cannot be excluded. (C) 2000 Academic Press.