DOPAMINE REDUCES INTENSITY OF SEROTONIN-INDUCED SPAWNING IN THE ZEBRA MUSSEL DREISSENA-POLYMORPHA (PALLAS)

The effect of dopamine (DA) on serotonin (5-HT)-induced spawning in the zebra mussel Dreissena polymorpha (Pallas) was tested. Administration of 1 mM DA with either 0.3 mM or 0.5 mM 5-HT significantly delayed spawning and reduced its intensity in both males and females compared with 5-HT controls. In dose-response experiments, a minimal DA concentration of 0.3 mM was necessary to delay spawning and reduce male spawning intensity to levels below that of the 5-HT control. Mussels treated with 5-HT-DA or DA alone opened their valves initially, but after 1 hour most valves were closed and both inhalent and exhalent siphons appeared extended, squeezed, and narrow, with reduced aperture openings. Possible mechanisms for the observed reduction in spawning intensity are discussed.