Physiological studies on transduction of tidal stimuli in the brain of a tropical wrasse

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The aim of the present study was to clarify how tidal stimuli are transduced endogenous signals in order to repeat daily spawning at high tide. To gain insight into these issues, the involvement of monoamines in mediating endogenous day-night and tidal rhythms in the threespot wrasse, Halichoeres trimaculatus, were examined. DA activity increased during the day and decrease during the night for fish held under a natural photoperiod. Intraperitoneal injection of melatonin resulted in a significant reduction in DOPAC/DA. Furthermore, DOPAC/DA was significantly lower in fish held at 3 m compared to 0 m depth, suggesting that hydrostatic pressure influences DA metabolic rate. These results indicate that light and hydrostatic pressure control dopaminergic turnover in the brain of threespot wrasse. Day-night and tidal changes in these two factors therefore may be the main environmental cues the fish uses to synchronize its spawning activity.