A rare catfish has been found to have a very odd way of predating on other fish.
The Gulper driftwood catfish, Asterophysus batrachus, has an enormous mouth and is capable of swallowing prey fishes that are massive in relation to its own size.
New research published by Zuanon and Sazima in the Journal of Ichthyology has shown for the first time exactly how the weird auchenipterid catfish manages to squeeze in such a big mouthful - it opens its mouth and the prey swims in.
By studying the fish, which has been dubbed the Ogre catfish, in an aquarium, Sazima and Zuanon were able to watch how A. batrachus swallowed such large prey and managed to cram them inside its stomach.
Says Sazima: "Asterophysus batrachus uses its cavernous gape in a remarkable way, scooping up large unaware prey headfirst, then taking advantage of the fleeing response to further the prey's advance into its stomach."
The stomach of the catfish is very distensible, so it often becomes extremely mishapen following the ingestion of another fish.
The authors say that the catfish also folds its prey in half once inside the belly in order to fit the entire fish inside.
This technique isn't unique to this species, however. Practical Fishkeeping has previously reported research on a predatory herring called Chirocentrodon bleekerianus, and others have recorded the behaviour among certain characins.
Sazima and Zuanon say that the belly of the fish changes in shape and becomes flacid following a large meal: "A fasting catfish occasionally takes in water, bulging its belly considerably ("belly ballooning").
"After a while, the fish expels the water entirely, along with a little mucus and a few small fragments of food. The wrinkled belly quickly regains its former shape."
For more details see the paper: Zuanon, J and I Sazima (2005) - The ogre catfish: prey scooping by the auchenipterid Asterophysus batrachus. Aqua. Journal of Ichthyology 10: 15-22.