In an article published by PLoS ONE, a French team comprising members of two joint research units (Laboratoire Evolution et diversité biologique - EDB, (CNRS/Univ Toulouse3/Ecole nationale formation agronomique and Laboratoire d'écologie fonctionnelle et environnement - ECOLAB (CNRS/Univ Toulouse3/ INP Toulouse/ INRA) report a predation behaviour never seen before: catfish that briefly come out of the water to catch pigeons
Photo: A sheatfish (right) surreptitiously approaches a group of pigeons © Camille Musseau
Some aquatic animals develop bold strategies to capture prey that is outside their ecosystem, i.e. out of the water. This is the case, for example, of some killer whales that are able to strand voluntarily to catch seals or sea lions on the shore.
The article published by PLoS ONE describes for the first time a similar behaviour in freshwater, in gleaned catfish. Wels, the largest freshwater fish in Europe, have been observed gushing onto the shore to catch pigeons and then dragging them into the water to eat them.
From a bridge in Albi, the authors of the study watched over a small island on the Tarn, a river where wels catfish were recently implanted, in 1983. On this island pigeons gather to drink and groom themselves. During 24 observation sessions of three hours each, the researchers recorded 54 pigeon attacks, 15 of which were successful. The fastest attacks lasted less than a second. During these acts of predation, it is not uncommon for the catfish to pull more than half of its body out of the water. According to the researchers, the fish only preys on active birds and neglects immobile pigeons, suggesting that it locates them not with its visual system but through the vibrations of the water they produce when they move.
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Stable carbon and nitrogen isotope analyses of 14 catfish at the observation site and their potential prey indicate that for some of these fish, the pigeon has become the predominant component of the diet. Although the reasons for this novel predation behaviour remain unknown, the study shows a remarkable adaptation of the catfish to its new environment.
Reference : "Freshwater Killer Whales: beaching behavior of an alien fish to hunt land birds, PLoS ONE, Julien Cucherousset, Stéphanie Boulêtreau, Frédéric Azémar, Arthur Compin, Mathieu Guillaume & Frédéric Santoul. (Source: CNRS / Dec 2012)