Just your garden-variety poisonous catfish

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Above, Northern Madtom (Noturus stigmosus), a venomous catfish species, collected from the Huron River near Ann Arbor, Michigan. New research suggests there are at least 1,250 and possibly more than 1,600 species of catfish that may be venomous and can inflict a painful sting. 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.

U. MICHIGAN (US)—Venomous catfish are far more common than previously thought, a new study finds.

The good news is that most use their venom as a self-defense mechanism against predatory fish and not in an aggressive way, says Jeremy Wright, a graduate student at the University of Michigan.

Wright’s research, which was published online Dec. 4 in the open access journal BMC Evolutionary Biology, says at least 1,250 and possibly more than 1,600 species of catfish may be venomous and can inflict a painful sting.

In other parts of the world, some catfish have extremely toxic venoms that can be deadly to humans.

Using  histological and toxicological techniques, as well as previous studies of evolutionary relationships among catfish species, Wright cataloged the presence of venom glands and investigated biological effects.

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, Wright explains.

When a spine jabs a potential predator, the membrane surrounding the venom gland cells is torn, releasing venom into the wound.

In his paper, Wright describes how catfish venoms poison nerves and break down red blood cells, producing such effects as severe pain, reduced blood flow, muscle spasms, and respiratory distress.

However, because none of the species he examined produces more than three distinct toxins in its venom, each species probably displays only a subset of the whole repertoire of effects.

The main dangers to humans who tangle with North American catfish 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, Wright says.

“In such cases, complications associated with these infections and foreign bodies can last several months.”

On the evolutionary side, Wright’s analyses point to at least two independent origins of catfish venom glands. In addition, the toxic proteins show strong similarities with, and might be derived from, previously characterized toxins found in catfish skin secretions.

Surprisingly, those toxins in catfish skin secretions have actually been shown to accelerate wound healing in humans.

While it’s possible that the proteins from their venom glands could have similar properties, it’s probably not very likely, given the known effects of these venoms on humans, Wright says, although it may be worth further investigation.

“I’m currently working to isolate particular toxins and determine their chemical structures and the genes responsible for their production,” he says.

“It’s a very poorly-studied area, with little in the way of scientific literature to draw on, and my studies are just getting off the ground.

“So at this point it remains to be seen whether they’ll have any therapeutic value, though it’s worth pointing out that toxins from the venoms of other organisms—snakes, cone snails, and scorpions, for example—have all been put to pharmaceutical and therapeutic use.”

Further examination of the chemical composition of the venoms also will provide valuable insight into the mechanisms and potential selective factors driving venom evolution in fishes, Wright says.

Wright received financial support from the Museum of Zoology and the Rackham Graduate School, both at the University of Michigan.

University of Michigan news: www.umich.edu/news/