Asterophysus

Background

The gulper catfish is a strict carnivore that feeds mostly on other fish, swallowing them whole. Its ability to engulf exceptionally large prey is made possible by specialized features including a loosely connected dentary symphysis, slight mobility of the premaxillae, and a highly flexible midpoint connection at the ventral side of the pectoral girdle. Potential prey fish apparently do not recognize it as dangerous, partly due to its slow, unobtrusive approach.

A commonly observed attack involves the catfish quickly turning sideways and biting the head of the targeted fish; if the first attempt fails, it does not pursue, but the prey often still does not perceive the threat, allowing the same approach to be reused. Once the prey is engulfed head-first, fine backwards-pointing teeth prevent escape, and the prey's struggles push it further into the greatly extendable stomach, where it ends up folded. The fully extended stomach may impair swimming.

Another observed ambush technique involves hiding in crevices between rocks and darting out to catch passing prey, such as freshwater angelfish. The species has also been observed swallowing large amounts of water and later expelling it with remains of earlier prey. In aquariums, it feeds during both day and night, but it is suspected to be nocturnal or crepuscular in the wild, giving it an advantage when hunting along river banks for sleeping prey.