The isopod enters as a juvenile through the gill slits. A female attaches to the tongue and feeds on blood from the arteries supplying it; the deprived organ atrophies and eventually falls away. The parasite then anchors its pereopods to the remaining stub of muscle and occupies the position the tongue held.
What follows is what makes the species unique among known parasites. The fish continues to feed, and the isopod's body appears to function mechanically much as the tongue did, pressing food against the roof of the mouth. Infested fish are not obviously debilitated in the way a tongue-less fish would be, though growth can be reduced in heavily parasitised individuals.
Much of the popular account is overstated. The isopod is not known to move on to eat the rest of the fish, it poses no danger to people handling or eating fish, and reports of live specimens found in supermarket snapper are occasional curiosities rather than a hazard. Life-cycle details, including how males and females pair inside a host, remain incompletely described.