Brazilian ichthyologists have described a new species of tetra that is thought to mimic another tetra species in order to avoid predation.
The new tetra, described in a recent issue of the Journal of Fish Biology, has been named Moenkhausia pirauba, and is hypothesised to mimic the colour pattern of Jupiaba apenima according to authors Angel Zanata, José Birindelli and Cristiano Moreira.
Moenkhausia pirauba, from the Xingu and the Tapajós river drainages, is distinguished from congeners except M. moisae in having more scales in the lateral series (43–47 vs. 23–41). It differs from M. moisae in its colour pattern and the scales along the mid-dorsal line between the tip of the supraoccipital process and the origin of the dorsal fin forming a regular series (vs. predorsal line of scales irregular, not forming a median series).
The new species was collected in clear-water creeks and small tributaries of larger rivers, usually in shaded pools between rapids with well-preserved riparian vegetation. Stomach contents consisted of adults of terrestrial insects, aquatic insect larvae, fish remains and plant fragments.
The species name is formed from the Tupi words pira (fish) and aúba (false), in allusion to its apparent mimicry with Jupiaba.
The colour patterns of M. pirauba and J. apenima are nearly identical to each other. Because J. apenima have strong spine-like pelvic bones that may serve as an antipredator mechanism (by making the fish harder to swallow), the authors hypothesise that the Moenkhausia tetra mimics the colour pattern of the Jupiaba tetra to fool predators. This form of mimicry where a palatable species mimics an unpalatable one is known as Batesian mimicry.
Additional evidence for the hypothesis of Batesian mimicry among these species is the fact that they have been observed in mixed shoals.
For more information, see the paper: Zanata, AM, JLO Birindelli and CR Moreira (2009) New species of Moenkhausia Eigenmann (Characiformes: Characidae) from Rio Xingu and Rio Tapajós basins, Brazil, with comments on a putative case of polymorphic Batesian mimicry. Journal of Fish Biology 75, pp. 2615–2628.