Catfish

Catfish belong to the order Siluriformes, a diverse group of ray-finned fish. They are most famous for their barbels, which are whisker-like sensory organs. While not every species has prominent barbels, they are a defining feature for many.

Unlike most other fish, Siluriformes lack scales. Instead, they possess either smooth, mucus-covered skin or protective armor-plated bodies. Scientists classify this order based on specific skull features and the structure of the swimbladder. This group is incredibly varied, ranging from tiny parasites to some of the largest freshwater fish in the world.

Most catfish are benthic feeders, meaning they live and hunt on the bottom. They are often negatively buoyant, which means they tend to sink rather than float. This is caused by a reduced gas bladder and a heavy, bony head.

Many species have a cylindrical body with a flattened ventrum, or underside. This shape helps them stay stable while feeding on the substrate. Some families, such as Loricariidae, have evolved a specialized suckermouth. This allows them to fasten themselves to objects in very fast-moving water.

Instead of biting or cutting prey with teeth, most catfish use suction or gulping to eat.

The skin of a catfish provides different types of protection. Some species rely on cutaneous respiration, where they breathe through their mucus-covered skin. Others have evolved bony plates called scutes for armor. In the genus Sisor, these plates are often supported by vertebral processes. In the subfamily Doumeinae, the armor is formed entirely by expanded vertebral processes.

Other species, like the doradids, possess lateral armor made of thickened ossicles. This variety in skin structure shows how different species have adapted to their specific environments.

Catfish use complex sensory systems to navigate and find food. Their barbels are highly sensitive to chemicals in the water. Many larger species have chemoreceptors across their entire bodies, including their barbels. This allows them to "taste" and "smell" their surroundings to locate prey.

Because these chemical senses are so vital, many catfish have very small eyes. Some species living in underground caves have lost their eyes entirely. They also possess a Weberian apparatus, which is a structure that connects the swimbladder to the ear. This allows for improved hearing and sound production.

Defense is another major aspect of catfish biology. Most catfish possess a strong, hollow, bony spine on their dorsal and pectoral fins. They can lock these spines into place to stick outwards. This makes it difficult for predators to swallow them.

In about half of all catfish species, these spines are venomous. Glandular cells in the skin cover the spines and produce a stinging protein. In the species Plotosus lineatus, a sting from these spines can be fatal to humans. This makes Siluriformes the vertebrate order with the largest number of venomous species.

The size range within Siluriformes is massive. The Mekong giant catfish from Southeast Asia is one of the largest species alive. In contrast, some members of the Trichomycteridae family reach maturity at only 10 millimeters.

Historical records and mythology often describe the wels catfish as having astounding proportions. While many of these stories are unverified, real specimens are quite large. For example, a wels catfish weighing 70 pounds was caught in Spain in 2009. In the Missouri River, a blue catfish weighing 100 pounds was caught in 2010.

Catfish have significant connections to human industry and hobbies. Many large species, such as Pangasius and Clarias, are farmed or fished commercially for food.

Smaller species, like those in the genus Corydoras, are very popular in the aquarium hobby. However, this hobby has also led to the spread of invasive species. For instance, plecos from the genus Pterygoplichthys have become prolific invasives in many areas. This demonstrates how the movement of species can impact entire ecosystems.