Blind Catfish

Blind Catfish would be big, blind, and slimy mobs that would only spawn in subterranean lakes or underground pools of water. (for more info see Subterranean lakes idea). They would be numerous and swarm about your boat, waiting for you to drop some food into their mouths. Their eyes would be blank and they would have a slippery tan texture, and whiskers  coming off their face. 

   If you killed one it would drop raw catfish that would poison you if you ate it raw. It would also drop 1-3 slime balls. They would be a great food source (if you cook them) while doing long spelunking expeditions.