This timid little fish escapes predators by injecting them with opioid-laced venom

Fang blennies are small fish with big teeth. Specifically, they have two large canine teeth that jut out of their lower jaw. Since blenny fish are only about two inches long, these ‘fangs’ would be less than intimidating if not for the venom within. Blenny fish venom most likely causes a sudden drop in blood pressure in would-be predators, such as grouper fish, that have been bitten by blennies.

Source