Fishes of Wisconsin, Halloween Edition: Pirate Perch

Happy Fish Fry Day! Once again fish is on the menu here in Wisconsin and on our mind at the CFL blog. We’ve been working our way through the 13-foot-long “Fishes of Wisconsin” poster to bring you interesting morsels of information for every species of fishes found in Wisconsin. Today’s spooky story is brought to you by the fascinating pirate perch! (Not to be confused with the pirate party poised to take power in Iceland!)

Pirate perch on the "Fishes of Wisconsin" poster. Photo: Marilyn Larsen
Pirate perch on the “Fishes of Wisconsin” poster. Photo: Marilyn Larsen

Here in Wisconsin, these fish (note: they’re not actually perch)  occur mostly in the southwestern part of the state in an around the Mississippi and Wisconsin Rivers (although some have been some inland waterways up north). Their main range is in Gulf Coast and Southeastern U.S. states.
But let’s just skip right to the scary parts, shall we? This nocturnal, solitary and secretive fish is the only member of its entire family (aphredoderidae), it got its name because in aquariums, it tends to simply eat all of the other fishes and that’s not all – it has some frightfully (sorry, couldn’t resist) interesting features. We’ll start with a fact that is not for the squeamish and then to a more terrifying tidbit. First up:
The pirate perch has its anus in its throat
Pirate perch - this master of disguise has quite a few secrets. Photo: John Lyons, WDNR
Pirate perch – this master of disguise has quite a few secrets. Photo: John Lyons, WDNR

Well, okay, not “in” but “under.” Still, there’s really no way to sugarcoat this. While it is born with its anus (or urogenital opening) much closer to its anal fin, that opening eventually migrates towards the fish’s throat as it matures. This opening is used both for excretion and reproduction, so scientists first believed that, much like species of cavefish, the pirate perch would incubate its eggs in its gill cavities. It’s now known that the fish spawns in a more traditional fashion – depositing eggs and/or sperm in underwater root masses. Which makes the location of the anatomy in question all the more mysterious.
The pirate perch is invisible to its prey
Sure, we all know about camouflage or, at least, visible camouflage, but the pirate perch takes it to a whole new level. We’re not just talking about a fish hiding in the weeds or lurking just beneath unsuspecting victims. When we say invisible, we mean invisible! While the mechanism is not exactly understood, scientists think that the pirate perch likely used a technique called”chemical crypsis” to mask its smell and, essentially, hide in plain sight.
TTU's William Resetarits setting up the pirate perch experiment. Photo: Texas Tech University
TTU’s William Resetarits setting up the pirate perch experiment. Photo: Texas Tech University

In an ingenious experiment, researchers at Texas Tech University took pirate perch prey, like frogs and aquatic beetles, and plopped them in outdoor, artificial ponds. They then introduced different species of fishes to those ponds, plunking down plastic tubs covered with mesh so that the frogs and beetles couldn’t see the fish but could “smell” their various chemical signatures. In every scenario, except for one, the frogs and beetles responded by sensing danger and not laying eggs near these enclosures. That one? Pirate perch, of course! Even though they were sharing the same space as a voracious predator, the frogs and beetles acted as if the pirate perch weren’t there at all.
Scientists are still trying to figure out the exact mechanism behind this disappearing act, but one thing is for sure – the pirate perch is an awesome Wisconsin fish and, as a predator, it seems to be taking cues from a movie of the same name and hiding in plain sight.