Fangblenny fish aren't just a cute face. They use special opioid-based venom to avoid being eaten.
http://www.npr.org/sections/thetwo-way/2017/03/31/521793691/a-tiny-fish-with-fearsome-fangs-uses-an-opioid-like-venom-to-escape-enemies
http://www.npr.org/sections/thetwo-way/2017/03/31/521793691/a-tiny-fish-with-fearsome-fangs-uses-an-opioid-like-venom-to-escape-enemies