We didn’t mean to make this week all about parasites, honest. It just happened that way. Rebecca wrote a thing, and then I – being a parasitologist after all – attached myself to her, and then Craig was all like “Hey, how do I get in on this?” and then the next thing you know its theme week at DeepSN. Well what the heck, lets keep it rolling.

So how about those oarfish huh? Two washing up in the same week; it must be The End Times, because, you know, two is a trend and all that, CNN says so. Actually, I am pretty sure that will prove to be nothing more than probability rearing its beautiful head. If, like CNN, confirmation bias makes that coincidence hard for you to swallow, then I highly recommend you read Leonard Mlodinow’s The Drunkards Walk; it’s a really interesting look at how probability and chance impinge on our daily lives.

One very lucky bunch of students had a once in a lifetime chance after the oarfish bodies washed up – the opportunity to help one of the world’s best known parasitologists, Armand Kuris of UCSB, to pull some worms out of a fish that has only been examined for parasites a couple of times ever. I for one would have loved to join them. So what did they find?

In short: some larval tapeworms and an acanthocephalan in the gut. The baby tapeworms mature in sharks, so in this case the oarfish would be acting as intermediate host. The acanthocephalan was an adult, and the oarfish likely got it from eating a prey item, probably a small fish or shrimp, in which the larval stage, or cystacanth, would have been hiding.

These findings are stunning in their supreme average-ness! No radical weirdo worm never seen before, no giant elongated beastie as befits the longest bony fish in existence, just a few run-of-the-mill fish parasites you can find in any old teleost. The larval tapeworms, in particular, are among the most common parasites found in marine fishes. At the intermediate stage they are not at all fussy and as such they show up in the guts of all sorts of fish. Literally, ALL sorts of fish. Acanthocephalans are a bit more interesting. Those are a minor phylum known well to parasitologists but not really many other folks. They are characterised by having a body cavity (like nematodes but unlike tapeworms), but no gut (like tapeworms but unlike nematodes). their most distinctive characteristic is a wicked spiny proboscis that they use to attach to the gut wall. Here’s a selection:

The biggest thing to take away from the oarfish necropsy is that they are, in essence, just like every other fish – full of parasites. As I like to say, NO FISH IS AN ISLAND, they are all mobile habitat patches for all manner of little beasties. The world’s 28,000 or so fish species may host 140,000 parasite species or more. I explain how here, and there’s a handy graphic about which bugs live where. In having these parasites, this very special fish proves that it’s not so special after all. In a very real sense, it’s just another piece of meat.

