Whale sharks, the world's biggest fish, are dealing with a pain in the butt – in the form of fish that try to rush into their poop chute whenever they try to take a dump. The cloaca-raiding remora is the guilty party, and while whale shark behavior appears to demonstrate they don’t enjoy it, relations between these two very different fish remain largely positive.

If you weren’t already aware, whale sharks are absolutely massive. Despite weighing up to 20.6 tons (18.7 metric tonnes) and stretching as far as 12 meters (40 feet), they roam the oceans scooping up small shrimp, fish, and plankton with their tiny teeth (they also have teeth on their eyes).

Though whale sharks are not rough and tough predators, hanging around with them still confers some protection for remoras, as would-be predators are deterred by their sheer enormity. So, a good deal for the remoras, but what does the whale shark get out of it?

Remoras are famously good cleaners, using a sucker on top of their head to cling to the bodies of the megafauna they haunt. Dutifully attached, they rid large animals of parasites, helping their host to remain healthy while also scooping up some left-over scraps for themselves. They will also dine on the whale shark’s poop, which is where the lines get a little blurry for remora.

In a recent Tweet, whale shark researcher and Principal Scientist for the Marine Megafauna Foundation Dr Simon Pierce enlightened Twitter to one of the less desirable habits of remoras when it comes to whale shark defecation.

According to Pierce, given half a chance, remora will “dive head-first into the shark's cloaca at the first sign of a shart."

“I presume this to be uncomfortable,” he wrote.

To combat the lavatory lurkers, whale sharks in Mexico have been seen performing robust tail thrashes to scare away remora just as they’re about to let one rip. The shark then lets off what Pierce terms a “poopnado” before hurriedly zooming away and returning to feeding, remoras once again in tow.

While this might sound grim, butt raiding is certainly not unheard of in the deep blue. The colons of sea cucumbers are known to be occupied by pearlfish who apparently see the sphincter as a portal to prime real estate. It’s difficult to accuse an animal like the salp of having a butthole, but these jelly beings' insides are also used as hideouts for small fish.

So, take comfort the next time you have a stomach upset. As toilet anxieties go, things could be a lot worse.

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