Distribution

Throughout the world, in freshwater and seawater.

1. Tropical and subtropical seas; 
2. Bodies of freshwater in Africa; 
3. Freshwater and brackish water in Africa, Asia and Australia; 
4. Bodies of freshwater in South America; 
5. Bodies of freshwater in Asia; 
6. Bodies of freshwater in the Americas (Canada to Guatemala); 
7. Bodies of freshwater in Mexico and Central and South America; 
8. Tropical to subtropical Indo-Pacific, as well as bodies of freshwater in Australia and New Guinea;
9. Bodies of freshwater in Africa and Asia; 
10. Bodies of freshwater in Europe, Asia and Africa.

Fig. 4.32  Genidens genidens.

Biology

Smaller to large fish (Silurus glanis up to more than 3 m). Most species only live in freshwater. Mouth surrounded by barbels. Skin without scales, often underlaid by bony plates. There is a venomous spine in each of the two pectoral fins, as well as one at the front of the anterior dorsal fin. The latter is greatly reduced in clariids and silurids or may be entirely absent. These venomous spines are often serrated and covered by a tissue sheath in which the venom glands are embedded. In some species the spines may even be barbed, and can thus cause gaping wounds.

Catfishes are adapted to various environmental conditions in different types of water. They are found in both clear and muddy water, in cold or warm rivers and lakes, but also in brackish water zones and coral reefs. They are chiefly carnivorous and find their food by digging in the substrate. Marine Catfishes often form large communities that are constantly in motion in their search for food. 

Some species are said to inflict actively defensive stings when cornered.

Risk

Apart from the Freshwater rays of South America, Catfishes are the only freshwater fish that possess a true venom apparatus.

Accidents usually occur in fishermen. In many cases envenoming only manifests itself in transient pain (e.g. Arius sp., Noturus sp., Schilbeodes sp.). With some tropical species the pain can last several days (Netuma sp., Osteogeniosus sp., Pimelodus sp., Plotosus sp., Pterodoras sp., Selenaspis sp. etc.), and some of these species can cause wounds that heal poorly (in particular Plotosus sp.). In rare cases systemic envenoming may occur. Fatalities are said to have occurred due to stings from Plotosus lineatus, Pterodoras granulosus and Pimelodus clarias.

Literature (biological)

Copley 1958, Halstead 1953, 1988, Helfman 2009, McKinstry 1993, Sterba 1987