What you see in the pictures is a parasite called (Cymothoa exigua)

  This parasite enters the fish through the gills and then cuts the fish's tongue and becomes the new tongue, and thus takes over every food that the fish gets.

Once this happens, the fish becomes just a container to contain, nurture and feed the parasite until the fish dies of starvation and the parasite completes its task with a new victim..

Sometimes the fish asks for help from one of the cleaner shrimp called “Pederson shrimp”, who plays the role of a rescuer and extracts the parasite and kills it .