One of the bizarrest parasitic relationships you will ever see

My good colleague Janine Caira wrote a paper way back in 1997 about one of the strangest parasites ever recorded in an animal.  This paper has stuck with me ever since, I think because I saw the original photos when I visited the lab of one of the other co-authors George Benz, when he was with Tennessee Aquarium (he's now at Middle Tennessee State U.).  So, I thought I'd revive it for you guys; the story goes like this:

Janine and her co-author Nancy Kohler had received a report from a longliner of a really big foul-hooked shortfin mako caught near Montauk, NY.  (a shortfin is shown at right, from discovery.com, this one with plenty of parasitic copepods on the dorsal fin - it sucks to be a shark sometimes).  Now, Janine is the queen of tapeworm taxonomy in sharks and rays - believe it or not, there's lots of them - and had visited Montauk before to collect parasites during catch-and-kill shark tournaments held there.  To make the most of the unfortunate death of this mako, they raced across the sound from Connecticut to collect parasites from the beast.  It was a huge animal, nearly 900lbs, and during necropsy, as they say in the paper, they "were astonished to find two anguilliform fish in the lumen of the heart".  Thats right, eels; this shark had two eels living in the chambers of the heart!  These particular eels, called pugnose eels or Simonchelys parasitica, have been recorded before burrowing into the flesh of halibut and other large North Atlantic fishes (hence their species name), but never completely internal and certainly not in the lumen of the heart, so this was a truly remarkable find. 

Janine and her colleagues were unable to determine the path of entry, but they showed good evidence that the eels were alive in the heart prior to the shark being killed and put in the fridge, because their guts were full of blood and there were pathologic changes to the heart.  Their conclusion?  That this was a facultatively parasitic relationship.  In other words, the eels didn't need to be living in the sharks heart (that would be obligate parasitism), rather they took advantage of an opportunity to get a meal.  They proposed that the eels probably attacked the shark after it had been hooked and was dangling, distressed, from the longline.  They had some evidence that the shark was probably resting on the bottom, which may have made it easier for the eels to find.  The pugnoses somehow gained entry (hypothesised to be through the gills) and made their way to the heart, where they dined on the beasts blood up until it died.  Maybe they would have burrowed out again after the animal expired, maybe they would have suffocated (remember - the eels had be swimming in and breathing the sharks blood once they were inside, how bizarre is that?).  We'll never know because the carcass went in the fridge, which ended things for the eels, but also led to this amazing discovery.

The horrifying part is that the shark was almost certainly alive as the eels made their way into its flesh and began to consume its life blood from the inside.  It would have been a long, slow and nasty way to go out.  It just goes to show that even when you are at the top of the food chain, you're never really at the top of the food chain...

Caira, J., Benz, G., Borucinska, J., & Kohler, N. (1997). Pugnose eels, Simenchelys parasiticus (Synaphobranchidae) from the heart of a shortfin mako, Isurus oxyrinchus (Lamnidae) Environmental Biology of Fishes, 49 (1), 139-144 DOI: 10.1023/A:1007398609346

Comments

[Daniel Bassett]

Thats incredible!!! Its almost unbelievable.

[Al Dove]

I can tell you they seriously doubted themselves at first, and bounced it back and forth and off lots of colleagues with a healthy dose of self-skepticism, but its for real. The part I struggle with is the eels swimming in the bloodstream, breathing it, getting in their eyes, and so on. As a disease person I can't help imagining all the immune effector molecules attacking them, and so on. Blood just isnt water, you know?

[Anonymous]

What are the parasites attached to the dorsal fin in the above picture. Guessing sea-lice but what genus?

[Al Dove]

No idea. They're certainly copepods, so sea lice of a sort, but its hard to tell without a closer look. They look a bit like penellids, which you often see on big pelagic things. A quick look in the literature for "copepod" and "parasit*" and "mako" only turned up Dinemoura, which is in the right group, but I'm not familiar with that bug so I could be way off.

[Anonymous]

At first I was like some guy on the Internets had a friend who wrote a paper 15 years ago about some eels living in the heart of a shark. Seems legit. But when googling.. it's in wikipedia too (http://en.wikipedia.org/wiki/Snubnosed_eel#Biology_and_ecology) so maybe it did happen. Maybe it's just one of those freak accidents that happened once and never again.

[Al Dove]

Hey anon - it does have that "too bizarre to be true" aspect to it, doesn't it? Maybe it did happen just the once, but as Janine and friends point out in their closing remarks - its exactly these kinds of bizarre events that are the raw material on which evolution feeds.

[Mark]

i suppose the only way to find out for sure is to force the situation in a controlled environment, obviously not the most ethical of experiments but I'd truly love to know the outcome... i agree entirely it certainly is "kinds of bizarre events that are the raw material on which evolution feeds"

[Anonymous]

http://en.wikipedia.org/wiki/Montauk_Project

Caught near Montauk, NY. Must be a government experiment!

[elliethebug]

Cool!

[over50dating]

great post....