Increased plasma 17-hydroxyprogesterone and milt production in response to gonadotropin-releasing hormone agonist in captive male starry flounder, Platichthys stellatus

S.H. Moon, H.K. Lim, J.Y. Kwon, J.K. Lee, Y.J. Chang-2003
Aquaculture, 218(1-4): 703-716

Abstract:

In captivity, reproduction of male fish is often dysfunctional, resulting in abnormally viscous milt. Treatment with exogenous gonadotropin or gonadotropin-releasing hormone agonist (GnRHa) has been found useful in overcoming this reproductive failure in some fish species. In this study, captive male starry flounder (Platichthys stellatus) were treated with GnRHa at three different dosages (50, 100 or 200 g kg^-1 fish body weight) by implantation with cholesterol pellets during their natural spawning season. The GnRHa treatment increased the levels of plasma testosterone (T) at the early spawning season and plasma 17-hydroxyprogesterone (17P4) throughout the spawning season. Both milt volume and sperm count were increased in a dose-dependent manner by GnRHa treatment, but the increase of milt volume was twice as rapid as the increase of sperm count. The treatment decreased sperm concentration. The increased milt volume was strongly correlated with the level of plasma 17P4 (r=0.690), but not with T (r=0.250). The level of 17P4 was also associated with sperm motility. The sperm obtained both from control and GnRHa-treated groups was used to fertilize starry flounder eggs, and the resultant embryos were grown until metamorphosis. No negative effects of the GnRHa treatment on fertilization, hatching and larval growth were found. The results suggest that GnRHa treatment can render captive male flounders to recover their ability to hydrate milt.

(Department of Aquaculture, Pukyong National University, Pusan 608-737, South Korea, e-mail of Y.J. Chang: yjchang@pknu.ac.kr)

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