Immunocytochemical studies of the gonadotropic cells in the pituitary gland of male mullet, Mugil cephalus, during the annual reproductive cycle in both natural habitat and captivity

Using antiserum specific for the beta subunit of coho salmon gonadotropic h ormone II (GTH II), an immunocytochemical study of Mugil cephalus (L.) pitu itaries was conducted during the annual reproductive cycle of the male in b oth natural habitat and captivity. The gonadotropic potency of the pituitar y gland in general underwent an obvious increase during testicular developm ent, reaching a peak at the time of reproductive maturity. During the testi cular cycle of M. cephalus, the GTH cells showed an increase in immunoreact ive staining intensity, granulation, hypertrophy and hyperplasia during sex ual maturation. However, degranulation, vacuolization, and weakened immunor eactivity of these cells occurred during spawning. The GTH cells in the pit uitary gland of M. cephalus males reared in captivity appeared with high sy nthetic and secretory activity but the reproductive activity declined, as r eflected in the form of low values of the gonadosomatic index (GSI) and ear lier resorption of the testes.