Researchers tally huge number ofvenomous fishes, tout potential for medicaltherapies5 July 2016

The Venomous Blue Tang (Paracanthurus), who stars inthe movie “Finding Dory.” . Credit: University of Kansas

Upon hearing the word "venom," most peopleprobably think of a snake's fang.

But the ability to produce and inject toxins intoanother animal is so useful, it has evolved multipletimes in creatures ranging from jellyfishes tospiders, shrews to the male platypus.

Now, a paper appearing this week in the journal Integrative and Comparative Biology catalogsinstances of venomous aquatic life, for the firsttime showing that venom has evolved 18 separatetimes in fresh and saltwater fishes.

Among the paper's other findings:

In contrast to squamates like lizards andsnakes, very few fishes have evolvedvenomous fangs or teethThe predominant function for venom infishes is defense rather than offenseVenom in freshwater is dominated bycatfishes, as opposed to marine

environments where it is widespread acrossmany groupsIt is surprising how comparatively commonvenom is in deep-sea sharks (30 percent ofvenomous sharks) compared to deep-seabony fishes (5 percent of venomous bonyfishes)

"For the first time ever, we looked at the evolutionof venom across all fishes," said lead authorWilliam Leo Smith, assistant curator at theUniversity of Kansas Biodiversity Institute. "Nobodyhad attempted to look across all fishes. Nobodyhad done sharks or included eels. Nobody hadlooked at them all and included all fishes in anevolutionary tree at the same time."

A close up of the venomous dorsal-fin spine in alanternshark (Etmopterus). Credit: W. Leo Smith andJennifer H. Stern

Smith and his KU co-authors Jennifer Stern andMatthew Girard, along with Matthew Davis of St.Cloud State University, spent years combingmedical reports of people exposed to venom from

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fishes. Then the team assembled the family treesfor those fish, using specimens from natural historymuseums to trace evidence of venom throughclosely related species.

"We figured out what a venom gland looks like in aknown-venomous animal and what it looks like in allrelated groups," the KU researcher said. "Forinstance, relatives of yellowtail that people eat assushi were reported as venomous, and we wereable to find venom glands in their spines."

Deep-sea one-jawed eel (Monognathus) is shown with avenomous fang on the roof of the mouth. Credit: W. LeoSmith

According to Smith, the 18 independent evolutionsof venom each pose an opportunity for drug makersto derive therapies for a host of human ailments.

"Fish venoms are often super complicated, bigmolecules that have big impact," he said. "Venomcan have impacts on blood pressure, cause localnecrosis, breakdown of tissue and blood, andhemolytic activity—it prevents clotting to spreadvenom around prey. Venom is a neurotoxin. Theaverage response is incredible pain and swelling."

According to Smith, because fishes have to livewith their own venom, "there might be helpermolecules that protect the fishes themselves andhelp them survive." He said these also could havetherapeutic value to people.

The last thing many fishes see, a head-on view of aVenomous Devil Firefish (Pterois). Credit: W. Leo Smith

Smith said that up to 95 percent of venomous fishuse their toxins defensively, usually gatheringvenom within their dorsal spines, where it can bedeployed in case the fish is crushed or another fishattempts to swallow it.

Some, however, use venom offensively to debilitatetheir prey and can sometimes injure people.

"Invasive lionfishes will orient themselves in astrange way and ram themselves at people," Smithsaid. "One-jawed eels have lost the upper jaw, butwith the lower one they slam prey up into amodified fang. Their venom gland sits right abovethe brain."

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Smith studies biological traits—like the ability tomake venom, fly or produce light—that have evolvedseparately in different lines of species. He saidvenom is distinct from poison because it typicallywon't harm an organism ingesting it; venom workswhen it comes into contact externally, somethingSmith himself has experienced when working in thepet trade (where most venom U.S. exposureoccurs), cleaning his own fish tank or collectingfishes during fieldwork.

"I've never been offensively stung," Smith said."The problem is they hide in the rocks in your fishtank, and you move the rocks. Or, when you'recollecting fishes. You're out there in the water witha mesh bag and a spear, trying to get venomousthings, and then a wave hits you and drives the bagof spines into your chest, and you say, 'Ah I regretthat.'"

More information: W. Leo Smith et al, Evolutionof Venomous Cartilaginous and Ray-Finned Fishes,Integrative and Comparative Biology (2016). DOI:10.1093/icb/icw070

Provided by University of KansasAPA citation: Researchers tally huge number of venomous fishes, tout potential for medical therapies(2016, July 5) retrieved 17 April 2022 from https://phys.org/news/2016-07-tally-huge-venomous-fishes-tout.html

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