Changes in serum concentrations and pituitary content of the two prolactins and growth hormone during the reproductive cycle in female tilapia, Oreochromis mossambicus, compared with changes during fasting

Patterns of change in serum concentrations and pituitary content of GH and two tilapia prolactins (PRL177 and PRL188) were examined during the reprodu ctive cycle of female tilapia, Oreochromis mossambicus, adapted to fresh wa ter and to seawater. Changes in these hormones during fasting were examined to elucidate whether changes observed during brooding could be attributed to a reduction in feeding during brooding. Serum concentrations of GH incre ased prior to pituitary content during the brooding phase of the reproducti ve cycle. In contrast, pituitary content of GH increased prior to serum con centrations during fasting. There was no consistent pattern of change in se rum or pituitary PRL levels during the reproductive cycle, among experiment s. Serum concentrations of PRL177 were elevated in all fasted fish, whereas PRL188 was elevated during fasting in males but not females. The increases in the serum concentration of PRLs and GH, and in the pituitary content of GH in response to fasting support the notion that these hormones are invol ved in the regulation of the use of metabolic substrates in tilapia. We con clude that reduced food intake during brooding may contribute to changes in serum and pituitary levels of the PRLs and GH observed during the reproduc tive cycle. Nevertheless, differences between changes in serum and pituitar y GH during brooding and fasting suggest GH has actions in reproduction, an d changes in GH during brooding are not only in response to fasting. (C) 19 99 Elsevier Science Inc. All rights reserved.