The Changes of Pituitary and Serum GTH Levels in the Reproductive Cycle in the Southern Catfish (Silurus meridionalis Chen)

The serum and pituitary samples of the Southern catfish(Silurus meridionalis Chen) GTH were measured using the radioimmunoassay for gonadotropin of African catfish(cfGTH), Clarias gariepinus, and the cfGTH standards were labeled using the same protocol for labeling common carp GTH, to investigate the endocrine regulation mechanism of gonadal development and maturation.Seasonal changes of serum GTH levels were consistent with seasonal changes of gonadsomatic indexes. During the breeding season the serum GTH levels were higher than those in other periods, and they reached the highest values in the spawning season. The pituitary GTH contents increased with the development of gonads, and reached the highest values in the maturation stage, and then decreased in the regressed stage. Significant differences between the male and the female pituitary GTH levels were only found in the late development stage and maturation stage.