Clarias

Clarias, a genus of air-breathing catfish belonging to the family Clariidae, derives its name from the Greek word "chlaros" meaning lively—a fitting moniker given that these fish can survive out of water for extended periods. The taxonomy of Clarias is paraphyletic, indicating that species from the genus Heterobranchus are intermixed within the Clarias group. These catfish are distributed across the Old World, with a significant presence in Africa.

One of the most notable species is the walking catfish, which has become a troublesome invasive pest in some regions where it was unintentionally introduced. Clarias catfish are easily recognizable by their eel-like bodies, elongated dorsal and anal fins, flat bony heads, broad mouths equipped with whisker-like barbels, and a specialized breathing organ formed from modified gill arches.

Currently, there are 61 recognized species within the Clarias genus, encompassing both extant and fossil species from Africa and Asia. Some species, such as Clarias batrachus, have been introduced to various parts of the world and have caused significant ecological disruptions. These invasive species can severely affect local ecosystems by preying on native fish, birds, and amphibians. For instance, in Florida, these catfish have invaded aquaculture farms, substantially reducing local fish populations. They have also been introduced to regions such as the United States, Indonesia, China, and Cuba, where they have caused similar environmental challenges.