A chamaeleon characin: The plant-clinging and colour-changing Ammocryptocharax elegans (Characidiinae: Crenuchidae)

Abstract

Most of the South American darters (Characidiinae) are drab-coloured, bottom-dwelling characins that lie in wait camouflaged against a predominately sandy or rocky substrate. In a striking contrast, Ammocryptocharax elegans differs from most characidiines by its ability to adopt a bright green colour while on submerged live plants. Moreover, it uses its narrow and curved-tip pectoral fins, as well as the pelvic fins, to cling to the leaves' margins and fine roots. Besides the "sit-and-wait" tactic recorded for species of Characidium, this darter often moves over the tridimensional substrate and scans it visually twisting the head slightly and moving the eyes sideways. While in a site with strong waterflow it moves in a hopping-like fashion over the substrate. On the other hand, it takes advantage of the slower current area created downstream of an obstacle (plant tufts, root tangles), where it hovers undulating its dorsal fin. While hovering, it moves upwards, downwards, and forwards, scanning the substrate for prey. Its diet is composed of minute aquatic immature insects. In predominantly green surroundings the Chamaeleon South American darter usually shows green attire, whereas on a darker root tangle or a dead leaf it has a drab, grayish or brownish pattern. © 2006 by Verlag Dr. Friedrich Pfeil.