18 December 2009

Sting of the cat: thousands of catfishes may be venomous

These lively, whiskery fishes are sometimes seen on our shores. It's best not to touch them as they can give you a nasty sting.
Lined eeltail catfishes (Plotosus lineatus)
Lined eeltail catfishes
(Plotosus lineatus) sometimes seen on our shores.

A new study found that at least 1,250 and possibly more than 1,600 species of catfish may be venomous, far more than previously believed. The main danger to humans come not from the initial sting, but from secondary infections arising from the puncture or pieces of spine breaking off in the wound. These complications can last several months.

Catfishes don't sting to catch their prey and only use their venom to defend themselves. So we are safe if we leave them alone. More about some catfishes found along our coasts.

Killer Catfish? Venomous Species Surprisingly Common, Study Finds
ScienceDaily 15 Dec 09;
Name all the venomous animals you can think of and you probably come up with snakes, spiders, bees, wasps and perhaps poisonous frogs. But catfish?

A new study by University of Michigan graduate student Jeremy Wright finds that at least 1,250 and possibly more than 1,600 species of catfish may be venomous -- far more than previously believed. The research is described in a paper published online Dec. 4 in the open access journal BMC Evolutionary Biology.

Lest anyone have concerns about attacks of killer catfish, rest assured that, at least in North America, these finned fatales use their venom mainly to defend themselves against predatory fish, though they can inflict a painful sting that many fishermen have suffered. In other parts of the world, some catfish do have extremely toxic venoms that can be deadly to humans.

Scientists have focused a great deal of attention of venom produced by snakes and spiders, but venomous fish had been largely neglected, said Wright, who used histological and toxicological techniques, as well as previous studies of evolutionary relationships among catfish species, to catalog the presence of venom glands and investigate their 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. 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 said. "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.

Those toxins in catfish skin secretions have been shown to accelerate wound healing in humans, so it's possible that the proteins from their venom glands could have similar properties. Probably not very likely, given the known effects of these venoms on humans, but perhaps worth investigating, Wright said.

"I'm currently working to isolate particular toxins and determine their chemical structures and the genes responsible for their production," he said. "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 said.

Wright received financial support from the U-M Museum of Zoology and the U-M Rackham Graduate School.

Poisonous Catfish Described
ScienceDaily 4 Dec 09;
In contrast to the exhaustive research into venom produced by snakes and spiders, venomous fish have been neglected and remain something of a mystery. Now, a study of 158 catfish species, published in the open access journal BMC Evolutionary Biology, has catalogued the presence of venom glands and investigated their biological effects.

Jeremy Wright, from the University of Michigan, USA, carried out the investigation. He said, "I used histological and toxicological techniques to elucidate the diversity and distribution of venomous catfish. I found that at least 1250, and possibly over 1600 species of catfish may be venomous, a number far greater than any previous estimate of venomous catfish diversity"

Catfish venom glands are found in association with sharp, bony spines along the leading edge of the dorsal and pectoral fins, which can be locked into place when the catfish is threatened. When a spine enters a potential predator, the membrane surrounding the venom gland cells is torn, releasing venom into the wound. Wright describes how catfish venoms are neurotoxic and hemolytic, and are capable of producing a variety of effects such as severe pain, ischemia, muscle spasm and respiratory distress. However, as any one species examined produces no more than three distinct toxins in its venom, each species may not display all of these properties.

Wright's analyses indicate that there are at least two independent evolutionary origins of catfish venom glands. In addition, the toxic peptides show strong similarities with, and might be derived from, previously characterized toxins found in catfish epidermal secretions. "Further examination of the chemical composition of the venoms will provide valuable insight into the mechanisms and potential selective factors driving venom evolution in fishes," comments Wright.

Diversity, phylogenetic distribution, and origins of venomous catfishes Jeremy J Wright

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