Seasonal Changes in Thyroid and Sex Steroids in Female Catfish, Clarias batrachus (Linnaeus) and Effects of Gnrh during Post-Spawning Period

Mature female catfish, Clarias batrachus were sampled monthly for one year to characterize changes occurring in the plasma concentration of sex steroid and thyroid hormones. Oocyte development was initiated during the month of February, continued until the time of spawning in May. Plasma estradiol and testosterone showed significant increase in February-March in association with the vitellogenesis; estradiol then remained elevated in pre-spawning animals, whereas testosterone returned to the levels that found in February.