Fishes are scared of this tiny animal, Here's why

You are looking at a parasite called the Cymothoa Exigua. It enters through a fish's gills, eats their tongue, and then replaces it with its body.

This lil stinker literally sucks out the blood from the fish's tongue, until it atrophies and falls off. The fish then attaches itself to the stub, becoming the fish's new tongue. Now every time the fish eats, it takes away a portion of the food for itself.