The Sequence of Appearance at Dawn and Disappearance at Dusk of Some Coral Reef Fishes

Abstract

Coral reef fishes were observed from the Hook Island Underwater Observatory and the light intensity and time at which each species appeared at dawn and disappeared at dusk were measured. For the species considered there was a definite sequence of disappearance at dusk (showing family groupings) that more or less reversed itself in the appearance at dawn. Light is probably a factor governing this behavior but whether it is light intensity, rate of change of light intensity, or a change in light quality (wavelength) is not known. It is postulated that the sequential appearance at dawn and disappearance at dusk of the fishes may have evolved to reduce confusion and hence the likelihood of predation at this time.