Relative concentrations of prolactin, gonadotropin and thyrotropin in the pituitary gland and blood serum during different phases of annual reproductive cycle in the freshwater catfish, Clarias batrachus.

Variations in prolactin content of the pituitary gland and blood serum were studied throughout a year in relation to the concentration of gonadotrophin and thyrotrophin hormones during the different phases of annual reproductive cycle in Clarias batrachus. Prolactin content showed a cyclic variation. Increasing trend in its potency kept pace with the rising concentration of gonadotrophin and thyrotrophin both in the pituitary gland and blood. Upward movement in the above hormones started with the onset of gonadal development from the preparatory phase, reached their peaks during spawning period and then began to subside with the approach of postspawning phase.