WHETHER FOR HEALTH OR PLEASURE, FISH SOMETIMES ENGAGE IN A PHENOMENON CALLED “FLASHING,” otherwise known as rubbingtheir bodies along the sea bottom.
Ned Deloach, in his estimable Reef Fish Behavior, describes it as an effort to deal with the irritation of parasites by scrapping them off, an alternative to the much more commonly seen symbiotic cleaning by small fishes and crustaceans.
Discussions about the cleaning dynamic sometimes suggest that, in addition to health benefits, the fish derive a pleasurable “tingly” sensation from a good cleaning and I’ve read somewhere that seafloor rubbing may do that.
IT’S PROBABLY ABOUT PARASITES
Maddeningly, I can’t find it. If you google “fish flashing” you get a lot of sites for home aquarium enthusiasts, where questions mostly yield answers about parasites, disease or, otherwise, a problem with the tank’s water.
A few suggest the backscratch possibility, but the answer most likely is that it’s to deal some physical issue.
On the other hand, I found this great video. And the little guy seems to be having a terrific time. I’m generally opposed to messing with sea life, but I’m envious of this one.
PRINCIPAL SOURCE: Reef Fish Behavior, Ned DeLoach