At least 1,250 species of catfish are venomous, a new study finds.
Most catfish use their venom for defense. Some in North America can inflict a sting that humans notice. Elsewhere in the world, a few catfish species can even kill humans.
The new count of venomous catfish — which may be more than 1,600, the scientists estimate — is much higher than thought.
The results are detailed in the journal BMC Evolutionary Biology.
Catfish venom glands are found alongside sharp, bony spines on the edges of the dorsal and pectoral fins, and these spines can be locked into place when the catfish is threatened. When a spine jabs a potential predator, the membrane surrounding the venom gland cells is torn, releasing venom into the wound.
Catfish venom poisons a victim's nerves and breaks down red blood cells, producing such effects as severe pain, reduced blood flow, muscle spasms and respiratory distress.
The main dangers to humans from North American catfish, however, come not from the initial sting and inflammation, but from secondary bacterial and fungal infections that can be introduced through the puncture wound or when pieces of the spine and other tissue break off in the wound, said University of Michigan graduate student Jeremy Wright, who led the research.
"In such cases, complications associated with these infections and foreign bodies can last several months," Wright said.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.