More fascinating mimicry: the filefish and the puffer. The little Mimic Filefish, Paraluteres prionurus not only looks like the toxic Black Saddled Toby, Canthigaster valentini, it is often found swimming around in tight little mixed groups of both species. When I started looking for the filefish, they turned out to be more common than I thought and I realized I had likely been seeing them all along but had been lumping them in with tobies. This is an example of Batesian mimicry in which a palatable species, the filefish, mimics a toxic species, the toby, which has tetradotoxin in its skin and other tissues. As a side note, I don’t know that all toby species are unpalatable to all predators because we have witnessed more than one being snarfed down by a lizardfish. So how to tell them apart? Let’s cover the easy identification clues first.
Filefishes have an elongate dorsal spine that can be raised and lowered, so if you can catch the fleeting moment when the fish raises the spine, you have your filefish. The above photo was taken during courting or a dispute, we couldn’t tell which, and the fish extended its the dorsal spine numerous times in the course of the chase.
The Black Saddled Toby is a member of the pufferfish family, Tetraodontidae, so a puffed up fish is a pretty good clue. They swell by rapidly drawing in water, but I can count on one hand the number of times I have seen a swollen pufferfish of any species. While this is a helpful clue on the rare occasion that it is encountered, what about all those other tobies and mimics swimming around together? How to tell them apart? Fins – look at their fins!
The toby’s dorsal and anal fins start well back toward the tail as marked in the above video frame capture.
The filefish’s dorsal and anal fins are more elongate, starting behind the eyes, about mid-body, and extending almost to the tail as marked in the above photo.
There are a few other identification clues. For example, male Black Saddled Tobies have blue, lined markings behind their eyes and mature (male?) Mimic Filefish have tiny spines at the base of their tails. But color patterns can vary and spines can be difficult to discern on a moving fish, so go with the fins. Want to see them in action and test your mastery of these identification clues? Check out this video from our BlennyWatcher YouTube channel. Side note: check out the scene where the toby puffs up and watch how quickly it expels the ingested water when it deflates: