Experimental Studies on the Reproduction of the Thin-Lipped Mullet, Liza ramada

Abstract

Like females of many commercially important fishes, Liza ramada fail to complete ovarian development and do not undergo final maturation (FOM), ovulation or spawning when reared in captivity. The aim of the present work was to investigate the histological and physiological changes during the reproductive cycle of Liza ramada reared in freshwater fish ponds and during induction of spawning in saline water. In the present study, the levels of total thyroxine (T4), triiodothyronine (T3) and cortisol in the plasma of Liza ramada in a complete reproductive cycle were measured in correlation with the seasonal histological changes in gonads. During the reproductive cycle of females, serum triiodothyronine (T3), thyroxine (T4) and cortisol decreased during ovarian early-vitellogenesis and increased during mid-vitellogenesis to reach a peak for both T4 and cortisol. Then, these hormones declined to low levels during late-vitellogenesis. At the prespawning stage, all mentioned hormones re-increased to high levels and finally declined during induction of spawning. There was a decrease in serum levels of thyroid and cortisol hormones coincided with an increase in testicular activity of the fish. T3 and T4 increased duringtestis ripening to reach a peak during spawning, while cortisol reached a peak during ripe stage and decreased to low levels during spawning. In conclusion, the seasonal changes in thyroid hormones and cortisol concomitant with gonadal maturation and spawning of Liza ramada support role for these hormones in reproduction and stress response of this fish.