Parasitic isopod on a rock cook - May 2021

Diving on the Mewstone at Plymouth, Devon
Here, I've photographed a rock cook (Centrolabrus exoletus) which is a small fish in the wrasse family. It has a hitchhiker in the form of a big parasitic isopod (Anilocra physodes).

This was photographed whilst diving on the Mewstone reef. The fish seemed to be swimming around happily enough in a small shoal of other rock cook, although it does look somewhat gruesome to see such a parasite.

Nikon D850, Nikkor 105mm