Cavefish

You catch Cavefish at Cirrusea. It is a Common fish, so you need a rod of level 1 or higher. It is carnivorous, so only carnivorous bait catches it: Earthworms, Bloodworms, Mealworms, Maggots, Baitfish and Pork Chop. When a Common fish takes carnivorous bait here, it is Cavefish 40% of the time.

In the Aquarium it earns 60 Gold an hour.

Dave can bring it back too, from a dive while your boat is at Cirrusea.