France’s Catfish Hunts down a Pigeon; Only fresh water fish of the Kind in universe

The term 'a fish out of water' describes someone taken from his natural
environment to one he's not comfortable in. But a group catfish in one odd ecological pocket have shown themselves to be rather comfortable with leaping on to dry land.

A study published yesterday investigates the remarkable phenomenon of the catfish that hunt pigeons. Catfish in south-west France have been spotted leaping from a river to snap up the unsuspecting birds, before wriggling back beneath the water to swallow them.

The unusual behaviour - similar to the way some marine mammals beach
themselves to snap up prey from the shore - has never been seen among catfish in their native range. It has led researchers the University of Toulouse to dub them 'freshwater killer whales'.

Between 1m and 1.5m long, European catfish are the largest freshwater fish on the continent and third largest in the world. Most catfish are bottom feeders, consuming aquatic plants, other fish, decaying vegetation, fish eggs and crayfish as well as snails, aquatic bugs and minnows.

However in the Tarn river, where they were introduced in the early Eighties, they seem have adapted their natural behaviour to capture prey in their new environment.  Researchers spent five months watching the catfish from a bridge over a small gravel island over a stretch of the Tarn passing through the city centre of Albi, an ancient town about 50 miles north-east of Toulouse.

Over that period they observed 54 beaching incidents, in which the catfish
managed to snapup a bird 28 per cent of the time, dragging them back into the water to gobble them up.

While the beachings were quick - lasting from less than one second to no more than four seconds - in about 40 per cent of cases the fish lunged so far from the water that more than half their bodies were exposed.

Catfish are named for the long, sensitive whiskers (known as barbels) around their mouths, and the those of the Tarn fish would perk up whenever they were hunting fish. That finding, combined with the fact that the fish only went for those pigeons who were moving, suggested the the catfish used water vibrations to hunt rather than visual cues.

While the study highlights an interesting example of unusual behaviour, the researchers said the ecological causes that have led to the unusual adaptation are still unknown Catfish were only introduced to the Tarn in 1983, and they now flourish there, leading the researchers to speculate that increased numbers of the fish could have led to a decline in marine prey.

The findings were reported yesterday in the open-access journal PLoS ONE.