Juveniles of the Bluespotted Trevally, Caranx bucculentus (Teleostei: Carangidae), schooling with venomous catfishes (Plotosidae): a new case of mimicry.

In 2006, at Lembeh Strait, Indonesia, juvenile trevallies (Carangidae) were first observed schooling with Striped Catfish, but the photographic images were too small to allow positive identification of the trevally species. On 6 April 2011, at a different site in Lembeh Strait, the same behavior was successfully documented with video (archived and available at http://dx.doi.org/10.5281/zenodo.1345288). The juvenile trevallies are the Bluespotted Trevally, Caranx bucculentus, a piscivorous Indo-West Pacific species known from Australia to Japan. This species differs from its congeners most obviously in having the straight part of the lateral line with enlarged scutes that extend anteriorly to below the first dorsal fin, combined with a very short, strongly arched, curved lateral line (Smith-Vaniz 1999). The prominent stripes of the trevally juveniles (Fig. 1) have not been observed previously in the species, clearly indicating alteration of the typical color pattern to more closely match that of the Striped Catfish.
Although the exact nature of the behavioral interaction is unknown, it is almost certainly a case of opportunistic rather than obligate mimicry. By traditional definition, this is a case of Batesian mimicry (Randall & Randall 1960, Moland et al. 2005, Randall 2005b), where a “harmless” species closely resembles a venomous species and thus is usually avoided by potential predators. Participation by the trevallies in the confusing compact catfish balls would also provide protection from predators. The relatively few numbers of trevallies compared to those of swarming catfish school would make it difficult for a predator to learn to distinguish the palatable juvenile trevallies. The trevallies may also be attracted to the catfish schools primarily because the schooling behavior flushes potential prey for both species. In addition to primarily Batesian mimicry, and perhaps some aggressive mimicry for approaching prey, there may also be an advantage in social mimicry, whereby the trevally mingles unobtrusively with the schooling catfish.