Alterations in diurnal pineal hydroxyindole-O-methyltransferase (HIOMT) activity in steelhead trout ( Salmo gairdneri) associated with changes in environmental background color

Abstract

1. 1. The effects of dark versus light background on pineal hydroxyindole- O-methyltransferase (HIOMT) activity was studied in steelhead trout. 2. 2. In an 8l:16D photoregimen a diurnal HIOMT rhythm persisted under both background conditions. However, the relative enzymatic activities during the light and dark portions of the photoperiod were in opposition. 3. 3. It is suggested that the background color plays an important role in the manifestation of the pineal HIOMT response to photoperiod seen in this species.