The gulper catfish is a strict carnivore that employs a unique feeding strategy. It swallows its prey, which consists mostly of other fish, whole. What's remarkable is that the prey can be exceptionally large, sometimes even larger than the gulper catfish itself. However, it's important to note that these attempts to consume prey larger than its own size can be unsuccessful.
The catfish captures its prey by biting on the head, and the fine, backwards-pointing teeth in its mouth prevent the prey from escaping. Instead, the struggles of the prey cause it to be further engulfed and eventually folded, with both its head and tail pointing towards the predator's head, inside the greatly extendable stomach of the gulper catfish. This unique stomach adaptation allows the catfish to accommodate prey of significant size. However, the fully extended stomach can lead to an abnormal appearance and may impair the catfish's swimming abilities. The gulper catfish may also ingest large amounts of water, which it later expels along with remnants of earlier prey.
Interestingly, potential prey fish are apparently unable to recognize the gulper catfish as a threat. This is likely because fish generally do not perceive other fish of roughly similar size as a major danger. Additionally, the gulper catfish adopts a slow and unobtrusive approach, which further contributes to the prey's lack of awareness. The catfish typically employs a common attack method where it quickly turns to the side and bites the head of the targeted fish. Even if the initial attempt fails, the gulper catfish does not pursue the prey. The prey, unaware of the catfish as a threat, can be caught using the same approach.
In some cases, observers have witnessed another hunting method employed by gulper catfish living in crevices between rocks, such as in the Atabapo River. These catfish dart out to catch passing prey, including angelfish. This behavior demonstrates their adaptability in different habitats.
In aquariums, gulper catfish will feed during both day and night. However, it is suspected that in the wild, they are primarily nocturnal and crepuscular, which gives them an additional advantage when hunting along river banks for prey that is often asleep.
Overall, the gulper catfish's feeding behavior and unique stomach adaptation make it a fascinating predator in aquatic ecosystems.