Is it true?
A quick google search turns up a few mentions, Wikipedia has a full sentence on venomous sharks, which cites an Oceana web page that cites a Monterey Bay Aquarium webpage which is not up anymore. Great. Immediately a dead end. And shame on Wikipedia for using such a crummy citation. Going beyond the link, we can find a mention of the venomous spine of the Pacific Dogfish shark on the Monterey Bay Aquarium page, but, alas, there is no citation here, just a single sentence where it is mention without details.
I have encountered this type of mention of the venom in dogfish spines without ever finding any research article on the subject, but, in truth, I have not looked very hard. I have dissected many an Atlantic Spiny Dogfish Shark (the type that would be swimming up the Thames River) however, and there is no venom gland or tubes to deliver the venom easily visible. Of course these things can be microscopic.
Now let’s dive into the literature to see if we can clear this up.
The earliest references I could find was a 1921 paper by Evans, The poison organs and venoms of venomous fish. Sounds promising.
From Evans 1921:
“Taking the spiny dogfish or spur-dog, we have a curved spine in relation to the anterior margin of its dorsal fins which is grooved on the posterior aspect extending a variable distance from the base. This groove contains a glandular structure, extracts of which can be proved to be venomous.”
Whoa, pay dirt.
Later in the same paper he explains:
“The injection into roach (the fish not the insect) of filtered glycerin extract of the gland substance obtained by scraping the groove of a dogfishes dorsal fin spine gave the following results.” Parentheses mine.
Here is a quick summary of his findings:
The fish lay quiescent for from 120 to 140 minutes.
Local swelling occurred.
One fish had muscles spasms.
Death appeared to be due to respiratory failure. He does not mention if all the fish he tested died, if fact he doesn’t even mention how many fish he tested.
But , alas, there actually may be venom associated with the spine of the dogfish. I am not familiar with the method he used, filtered glycerin extract of the glandular substance, but now I must look into it, and do some more research. But I thought springs to mind here, if you took a scraping, certainly bacterial filled, from a groove in the shark and injected it into a fish, wouldn’t you expect the fish to have some symptoms of this?
Maisey, published in 1979, tells us:
“Adult Squalus and Heterodontus finspines have a continuous (entire) cap apically, i.e., it entirely covers the spine apex anteriorly.”
But Maisey did speculate on the venom and glandular tissues, one bit of tissue is suspected was mucous producing and the other he thought could produce venom but it would be midl in toxicity since few clinical cases have been reported.
“No published data on selachian fin spine venom are available.“
He goes one to say:
“A strong defensive role for fin spines in juvenile squalids and heterodontids is suggested by their rapid development, making the young fishes both prickly and unpalatable, if not actually venomous.”
So he has doubts?
The venom, if it exists, will be hard to inject into a fish, since the cap of the spine is covered. The venom is, according to Evans, only in the groove which does not reach the spine tip. And after Evans work no one seems to have determined the chemical nature of the venom.
What research has been done on this since?
Halstead mentions in his Poisonous and Venomous Marine Animals of the World that Squalus megalops, another species within the dogfish genus, has inflicted injuries from its spine. This report is from an even earlier work, Paradice from 1924. There is no mention of venom just the injury.
Again, what research has been done on this since?
Long pause…
Has anyone determined what the toxin is? It appears not. Is there actually a toxin associated with the spines of these sharks; I doubt it.
Here is my hypothesis, the report from Evans that his scraping is derived from a venom gland, is bogus. The scraping, since injected, may have killed the fish but there no evidence that a venom actually did this. As mentioned above, would scrapings and subsequent injections of such cause harm? Probably.
Wait, there is more, my hypothesis may be bust. A couple of researchers, Haddad and Gadig, published a note of a fisherman possibly envenomed by a shark in the genus squalus.
They report a fisherman was injured while handling a shark. He had an injury on his hand. The fisherman reportedly felt great pain, more than the wound would cause, and the pain subsided over six hours. Besides this report, the researchers cite our friend Evans and an older study by Coutiére who says these fish can cause fatalities (yikes). These authors say that a study of the venom and evenoming should be carried out, I agree, because I still think that these sharks do not have venom. Do a study, show me that I’m wrong.
Sources and Further Readings
CNN news story.
https://www.cnn.com/travel/article/venomous-sharks-london-scli-intl-gbr-scn/index.html
Coutiére H. 1899. Poissons venimeux et poissons ve ́ne ́neux. The ́se. Agre ́g CArre ́ et Naud, Paris.
Evans HM. 1921. The poison organs and venoms of venomous fish. The British Medical Journal 2: 690–692.
Haddad jr. V and OBF Gadig. 2005. The spiny dogfish (squalus cubensis/megalops group): The evenoming of a fisherman, with taxonomic and toxicological comments on the Squalus genus. Toxicon 46: 828–830.
Halstead BW. 1970. Poisonous and Venomous Marine Animals of the World. Darwin Press.
Maisey JG. 1979. Finspine morphogenesis in squalid and heterodontid sharks. Zoological Journal of the Linnean Society 66: 161–183.
Paradice WEJ. 1924.-Injuries and lesions caused by the bites of animals and insects. Med. J01lj·. Australia: 650-652, 2 figs.
“Brief reports are made of the following cases: bites by eels, Chinaman fish poisoning, pricks from worms and gill rakers of fish, stabs from the spine of Squalus megalops, stings from sea urchins…”