Facts About Catfish Eating Habits

The nearly 2,900 living catfish species comprise one of the most species-rich vertebrate orders in the world -- the order Siluriformes. Worldwide, approximately one out of every four freshwater fish and one out of every 20 vertebrates is a catfish of some type. Catfish vary greatly in terms of size; the giant European wels (Silurus glanis) may exceed 15 feet in length, while some small forms -- known as banjo catfishes (Aspredinidae) -- mature at less than an inch in length.

Most catfish species have small eyes and primarily find food by using their barbells, sense of smell and sense of taste. Most species are omnivorous and consume a wide variety of foods -- typical catfish eat things like other fish, invertebrates, aquatic plants and fish eggs. However, some catfish, such as some species in the family Loricariidae, specialize on strange foods, such as wood and algae. Other catfish are parasitic and feed on the blood of other fish. Scientists have documented giant catfish, such as the European wels, consuming rodents, frogs and aquatic birds in addition to their typical prey species.

A 2001 study by Kirsten Pohlmann and colleagues from the University of Konstanz and the Boston University Marine Program, researched the prey-trailing behavior of European wels. Publishing their results in the “Proceedings of National Academy of Sciences of the United States of America,” the team found that -- in addition to using smell, taste and feel -- catfish trailed their prey by following the wake left by them. Because the prey fish did not exhibit any predator avoidance strategies before being eaten, the researchers concluded that the catfish remain undetected by their prey when hunting in such a manner.

The diet of catfish often changes as they age. Young channel catfish (Ictalurus punctatus) primarily feed on aquatic insects such as dragonfly larvae, water beetles and fly larvae. By the time they're adults, channel catfish consume small fish, seeds, aquatic plants, algae, crawfish and snails. In many bodies of water, once channel catfish exceed 18 inches in total length, fish serve as the most important component of their diet. Blue catfish (Ictalurus furcatus) exhibit a similar ontogenetic dietary shift; around 10 to 15 inches in length, they switch from invertebrate-based to fish-based diets.