Some South American fishes are taking the adage "you are what you eat" literally, according to a paper published in the most recent issue of the journal Neotropical Ichthyology.
Eduardo Bessa and coauthors have discovered that juvenile Dourado (Salminus brasiliensis), a predatory characin, are taking advantage of their similarity in colour pattern to the herbivorous Piraputanga (Brycon hilarii) and schooling with them in order to disguise themselves from their prey.
The two fish species share a dark streak running through the caudal peduncle and fin, as well as reddish fins.
The authors conducted more than 50 hours of underwater observations in clear headwater streams of the Paraguay River drainage in western Brazil.
During the observation sessions, they quantified the number of Dourados and Piraputangas in the mixed species schools, and measured the number of rushes against a prey by the Dourados in 12 sessions of observation lasting 15 minutes each time. The observations involved at least five different individuals and consisted of six instances of Dourados feeding among the Piraputangas and six instances apart from them.
The authors observed Dourados of up to 30cm/12" in length schooling amongst the Piraputangas, moving to the edges of the schools to attack tetras, and returning to the school in more than 90% of the instances observed.
The Dourados not only stayed longer among the Piraputangas compared to feeding alone, but also rushed more often against their prey when they were among the Piraputangas.
The more abundant Piraputangas do not threaten the tetras and probably serve as a source of camouflage for the juvenile Dourado, allowing aggressive mimicry to occur.
This form of aggressive mimicry was only evident in juvenile Dourados, as the large adult fishes stayed apart from the Piraputangas (who also actively avoided the large adult Dourados as the Pirapuntangas were very likely to be eaten).
For more information, see the paper: Bessa, E, LN Carvalho, J Sabino and P Tomazzelli, 2011. Juveniles of the piscivorous dourado Salminus brasiliensis mimic the piraputanga Brycon hilarii as an alternative predation tactic. Neotropical Ichthyology 9, pp. 351–354.
Why not take out a subscription to Practical Fishkeeping magazine? Check out our latest subscription offer.