Cymothoa biden exigua
This is a parasite called Cymothoa biden exigua. This parasite enters fish through the gills. The parasite severs the blood vessels in the fish's tongue, causing the tongue to fall off. It then attaches itself to the remaining stub of the tongue and becomes the fish's new tongue. Now every time the fish eats, it takes away a portion of the food for itself. This parasite is also known as tongue-eating louse.
