Does the bright spot on the back of young archer fishes serve group coherence?

Young archer fishes (Toxotes jaculatrix) and Toxotes chatareus) have a brig ht, yellow-green spot on their back, which disappears when they reach a len gth of about 3 cm. With respect to the function of this spot, two thitherto untested) theories have been brought forward: (a) the spot helps the fishe s to remain together; tb) the spot attracts insects on which the fish feeds . Because living in groups seems incompatible with the typical prey-catchin g behaviour of this species - squirting down insects - we tried to find out whether young archer fishes that are in possession of the spot stay togeth er. Therefore the locations of twenty subjects in a large aquarium were obs erved during several weeks. Gregrariousness, if any, was not prominent. This finding contradicts the th eory that the spot serves to keep the fishes together. The hypothesis that the spot attracts insects is discussed. It is suggested that the presence o f the spot could coincide with the emergence of squirting and that it could attract fireflies.