ABSTRACT
Involvement of pineal and its major hormone, melatonin, in the process of erythropoiesis in a freshwater catfish, Clarias batrachus has been investigated. The study was conducted during four phases, namely preparatory phase, spawning phase, postspawning phase and late postspawning phase of its annual reproductive cycle. During each phase a fish received either melatonin injections or subjected to pinealectomy. In addition, each fish in all the groups, received either iopanoic acid or cyproterone acetate or vehicle in the morning or late afternoon. Results clearly indicate that melatonin stimulates the rate of erythropoiesis in Clarias batrachus. It appears that the extent of stimulation depends upon the phase of the annual reproductive cycle. However, in general, the pineal- or melatonin-induced modulation of blood variables is gonad dependent and thyroid seems to play a time of the day dependent subtle role.