The Catfish

Nov 20, 2011 Features / Columnists, Interesting Creatures in Guyana

Catfishes (order Siluriformes) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat’s whiskers, catfish range in size and behaviour from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores (species that eat dead material on the bottom), and even to a tiny parasitic species commonly called the candiru, Vandellia cirrhosa.

The Catfish

There are armour-plated types and also naked types, neither having scales. Despite their name, not all catfish have prominent barbels; members of the Siluriformes order are defined by features of the skull and swim bladder. Catfish are of considerable commercial importance; many of the larger species are farmed or fished for food. Many of the smaller species, particularly the genus Corydoras, are important in the aquarium hobby. Extant catfish species live in inland or coastal waters of every continent except Antarctica. Catfish have inhabited all continents at one time or another. Catfish are most diverse in tropical South America, Africa, and Asia. More than half of all catfish species live in the Americas.
They are found in freshwater environments, though most inhabit shallow, running water. Representatives of at least eight families are hypogean (live underground) with three families that are also troglobitic (inhabiting caves).
Most catfish are bottom feeders. In general, they are negatively buoyant, which means that they will usually sink rather than float due to a reduced gas bladder and a heavy, bony head. Catfish have a variety of body shapes, though most have a cylindrical body with a flattened ventrum to allow for benthic feeding. A flattened head allows for digging through the substrate as well as perhaps serving as a hydrofoil. Most have a mouth that can expand to a large size and contains no incisiform teeth; catfish generally feed through suction or gulping rather than biting and cutting prey.
However, some families, notably Loricariidae and Astroblepidae, have a sucker mouth that allows them to fasten themselves to objects in fast-moving water. Catfish also have a maxilla reduced to a support for barbels; this means that they are unable to protrude their mouths as other fish such as carp. Catfish may have up to four pairs of barbels: nasal, maxillary (on each side of mouth), and two pairs of chin barbels, although pairs of barbels may be absent, depending on the species. Catfish also have chemo-receptors across their entire bodies, which mean they “taste” anything they touch and “smell” any chemicals in the water. “In catfish, gustation plays a primary role in the orientation and location of food”. Because their barbels and chemo-reception are more important in detecting food, the eyes on catfish are generally small.
Catfish have no scales; their bodies are often naked. In some species, the mucus-covered skin is used in cutaneous respiration, where the fish breathes through its skin. In some catfish, the skin is covered in bony plates called scutes; some form of body armor appears in various ways within the order.
Catfish have been widely caught and farmed for food for hundreds of years in Africa, Asia, Europe, and North America. Judgments as to the quality and flavour vary, with some food critics considering catfish as being excellent food, others dismiss them as watery and lacking in flavour.
Meanwhile, while the vast majority of catfish are harmless to humans, a few species are known to present some risk. Perhaps the most notorious of these is the Candiru, due to the way it is reputed to parasitize the urethra, though there is only one well-documented case of a candiru attack on a human.
Since 2007, the Goonch catfish has also gained attention following a series of fatal underwater attacks which have been alleged by biologist Jeremy Wade to have been from unusually large goonch.
The Wels catfish has also been reputed to kill humans (especially young children), and while there are no documented cases of fatalities, larger specimens are known to cause serious injuries in rare instances. In addition, other species are reputed to be dangerous to humans as well, but with less definitive evidence. Many catfish species have “stings” (actually non-venomous in most cases) embedded behind their fins; thus precautions must be taken when handling them.