Oreochromis leucostictus. The female mouth brooder releases the fully developed young from the mouth. The young follow their mother, often even touching her. Dummies are used to find out to what extent such factors as movement, shape, size and light intensity of the dummy differ in their releasing effect on unexperienced young fishes. The combination of particularly strong individual releasing characteristics have a "supernormal" effect, i. e., in an experiment where choices are offered, the young follow this dummy more readily than their mother waiting to receive them.