(As told to me by David Muirhead)
One of our members recently discovered a ‘yawning’ fish on some of their video footage. This is a snip of the fish from the video: –
The ‘yawning’ fish can be seen at the top right in this short video: –
“The ‘yawning’ fish is an adult Crested Threefin, Trinorfolkia cristatus, possibly male.
It is not actually yawning, or signalling to other fish, visible or otherwise. It’s eating some of the tiny crustaceans (e.g. copepods, isopods and mysids) that are teeming there. You can see the circuit-type swimming by the copepods, isopods and maybe mysids, as pale specs in the foreground in the video. The gulping action by the fish just looks like yawning.
We don’t know if fish actually yawn, but many species look like they yawn when doing any of several other behaviours
i.e. territorial disputes, courtship displays, winnowing, and ensuring that cleaner hosts get full access to lips, mouth and gills.
That’s 4 “yawn like actions “.
Another (possibility) would be ejecting something stuck in the mouth or throat e.g. a bit of indigestible crab shell after chomping a crab.
….. I don’t recall seeing any threefin, or goby, or blenny species seemingly yawning in communication of some sort with a disappearing Talma, but I don’t notice everything. Talmas and various smaller or similar size fish have overlapping diets, which might prompt a little threefin or goby, etc.. to try and keep Talma away from their ‘home patch’ by acting aggressively i.e. flashing their tiny but sharp teeth via a wide open mouth.
Talmas as you know have tiny mouths adapted for extracting tiny worms, crustaceans, molluscs, various polypoid things and other tiny invertebrate animals from their tight, often tubular homes on, for example, reefs and jetty piles. So they might feel threatened by even something much smaller with lots of visible, albeit tiny, teeth and a wide open mouth that is actually a big mouth relative to the total size/length of a threefin or blenny. Talmas certainly cannot open their mouths nearly as much in comparison. But I am only guessing.
Also it’s important not to mistake a threefin yawn for being directed at a Talma, just because it is facing in the Talma’s direction.The threefin could be warning off another nearby (but unseen by you, me or any observer) member of its own threefin species, and the Talma’s presence could be mere coincidence. But …. most of the above options are possible explanations.”