I was thinking about fishing in dungeons and how it’s basically fetid water fishing, which makes some sense, but I imagine in some dungeons the pool might be in a dark enough and deep enough area that it may be appropriate to have deep-sea fish, too.
Other reasons might give to their appropriateness to deep dungeon areas : a lot are ugly like monsters, some are fantastic and magical, others are bio-luminescent.
Fangtooth or Ogrefish
Deep sea dragonfish
Also stuff I hope to see.
Electric eels (In the oceans)
Players would get shocked by them.
Jellyfish (The sea-borne equivalent of the slime)
Here’s the best online screencap of a jellyfish I could find in Terraria, where they’re common in underground pools and are a light source…
Some type of jellyfish part like a radiant ‘jellyfish heart’ that emanates the light would make a good alchemy reagent.