Abstract
Young archer fishes (Toxotes jaculatrix and Toxotes chatareus) have a bright, yellow-green spot on their back which disappears when they reach a length of about 3 cm. With respect to the function of this spot, two (hitherto untested) theories have been brought forward: (a) the spot helps the fishes to remain together; (b) the spot attracts insects on which the fish feeds. Because living in groups seems incompatible with the typical prey-catching behaviour of this species - squirting down insects - we tried to find out whether young archer fishes that are in possession of the spot stay together. Therefore the locations of twenty subjects in a large aquarium were observed during several weeks. Gregariousness, if any, was not prominent. This finding contradicts the theory that the spot serves to keep the fishes together. The hypothesis that the spot attracts insects is discussed. It is suggested that the presence of the spot could coincide with the emergence of squirting and that it could attract fireflies.
