The Behaviour of Minnows in Relation to Light Intensity

Abstract

Minnows kept in a tank are active during the day and quiet at night. Their behaviour is reversed if they are given hollow bricks in which they take cover and so avoid bright light. When cover is available they are very active at sunrise and sunset. Minnows have no inherent daily rhythm of locomotory activity. Blind minnows respond to daily variations in light intensity, and are more active at night than during the day. Minnows will not cross a light-dark boundary when the intensity on the light side is greater than 0.17-0.08 m.c A minnow shoal disperses between intensities of 0.024 and 0.0034 m.c. Minnows catch Dapknia better in bright light than in the dark. The change from visual to ‘dark’ feeding takes place between 0.0007 and 0.00007 m.c. Minnows appear to avoid bright light by a comparison of intensities if the light-dark boundary is sharp, but they may also respond to light photokinetically. It should be noted that these results, obtained in the laboratory, may not be true for minnows under natural conditions.