The regulation of day–night changes in hydroxyindole-<i>O</i>-methyltransferase activity in the pineal gland of steelhead trout (<i>Salmo gairdneri</i>)

Abstract

Elevation in pineal hydroxyindole-O-methyltransferase (HIOMT; EC 2.1.1.4) activity in juvenile steelhead trout was associated with the dark portions of three different photoperiods with a sharp increase in pineal HIOMT activity occurring in the first 4 h of darkness. This pattern of activity could be abolished by bilateral enucleation but not by surgical capping of the pineal region. Surgical exposure of the pineal region in blinded fish did not restore HIOMT responses to changes in lighting.