Influence of season, gonadotropins, and gonadal hormones on the thyroid activity of freshwater perch, Anabas testudineus (Bloch)

Abstract

Perch thyroid activity fluctuated in different phases of the reproductive cycle, being highest at spawning and lowest at postspawning. Treatment of intact perch with salmon gonadotropin (SG-G100) or ovine luteinizing hormone (LH) (1 μg/100 g body weight) for 15 days markedly enhanced thyroid activity. The extent of stimulation was greater with SG-G 100 than with LH. Follicle-stimulating hormone (FSH) had no effect. Ovarian steroids, 17β-estradiol and estrone (100 ng/100 g body weight), also significantly augmented thyroid activity. There was a striking reduction of thyroid activity as a result of ovariectomy, a decrease that could not be improved by SG-G100; however, estrone or 17β-estradiol supplementation resulted in a significant increase of thyroid activity in comparison with ovariectomized controls. These findings suggest that gonadotropin mediated its stimulatory effect on perch thyroid activity via the release of ovarian steroids.