RHYTHMIC MELATONIN SECRETION IN DIFFERENT TELEOST SPECIES - AN IN-VITRO STUDY

The rhythmic production of melatonin is governed by intrapineal oscill ators in all fish species so far investigated except the rainbow trout . To determine whether the latter represents an exception among fish, we measured in vitro melatonin secretion in pineal organs of nine wild freshwater and six marine teleost species cultured at constant temper ature and under different photic conditions. The results demonstrate t hat pineal organs of all species maintain a rhythmic secretion of mela tonin under light:dark cycles and complete darkness, and strongly sugg est that most fish possess endogenous intrapineal oscillators driving the rhythm of melatonin production, with the exception of the rainbow trout.