Seasonal and daily variations in hypothalamic monoamine levels and monoamine oxidase activity in the teleost Channa punctatus (Bloch).

In Channa punctatus, a significant daily variation in hypothalamic 5-HT level and monoamine oxidase (MAO) activity was noticed in preparatory phase (February), but not in prespawning (May) or postspawning (November) phases. Hypothalamic dopamine (DA) and noradrenaline (NA), on the other hand, showed marked daily variation in their levels during all the three seasons with peak values in the photophase. The overall activity of MAO (mean +/- SEM on 24-hr period) increased from November to May through February, whereas the 5-HT content which was high in November decreased during February and May. The NA and DA levels were low in November and February and high in May. The catecholamine (CA) content and MAO activity increased with increasing photoperiod and temperature which is indicative of an enhanced CA metabolism.