In its natural habitat, Oligocottus maculosus displayed a locomotor activity that is dependent primarily upon such factors as turbulence, temperature, and light. Under laboratory conditions this species exhibits a tidal rhythm of locomotor activity. The rhythm appears to be entrained directly by the tide and is not directly related to the daily field activity of O. maculosus. It is concluded that it represents the coupling of an avoidance or escape response to a biological clock.