Asterophysus

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Asterophysus batrachus, known as the gulper catfish or ogre catfish, is a carnivorous catfish found in South America. It is listed as Least Concern and is the only described species in its genus Asterophysus.

Where it lives
This fish is native to the Rio Negro and Orinoco basins in Brazil, Colombia, and Venezuela. It prefers slow-moving water with lots of submerged structures and rocky crevices.

Size and appearance
It grows to about 25 cm in standard length (around 9.8 inches) and up to about 28.5 cm total length (11.2 inches). It has a dark body with a pale belly and a short, stocky shape.

Diet and feeding tricks
The gulper catfish is an obligate carnivore that swallows prey whole, often catching other fish. It can eat prey larger than itself thanks to a highly flexible mouth and jaw area that lets its oropharyngeal opening expand greatly. It typically bites prey headfirst; if the prey struggles, it is pulled further into the catfish’s large stomach. The fish may take in water with prey and later expel it along with remains. Other fish often don’t recognize it as a threat because it moves slowly and hides in crevices. In some observations, it hunts by dashing from rocky crevices to grab passing fish, including angelfish.

Behavior and habits
In the wild, it is thought to be nocturnal or crepuscular, which helps it hunt along riverbanks at times when prey are sleeping. In aquariums, it can feed during day or night.

Notes on classification
There is a specimen from Marajó that might belong to an undescribed species, but Asterophysus batrachus is currently the only described species in this genus. Locally, people often don’t eat it because they consider it ugly, but some people keep it in aquariums.