Plasma Testosterone Concentration Predicts the Ovulatory Response of Coho Salmon (Oncorhynchus kisutch) to Gonadotropin-Releasing Hormone Analog

Plasma concentrations of testosterone, 17α-hydroxy-20β-dihydroprogesterone (DHP), and estradiol-17β were determined in hatchery populations of adult female coho salmon (Oncorhynchus kisutch) before and after the fish were injected with gonadotropin-releasing hormone analog (GnRHa) to accelerate ovulation. Treatment with GnRHa significantly accelerated maturation over that observed in saline-injected controls; however, a number of females that received GnRHa did not ovulate for as long as 8 wk after treatment. Before treatment, the mean plasma levels of DHP did not differ between early- and late-ovulating females; estradiol differed sometimes, but not always; and testosterone was always higher in the early-ovulating fish. Thus, plasma concentrations of testosterone appear to be useful for predicting the sensitivity of coho salmon to GnRHa treatment for induced ovulation.