The Vorash is a colossal fish-like creature encountered as major boss battle in Metroid: Other M. It is always seen dwelling in bodies of lava.
First spotting the sea beast in a Pyrosphere tunnel, Samus Aran followed a Vorash and battled it in an ocean of lava, littered with obsidian platforms. A long time after the confrontation, the two battle again in the Blast Furnace Observation. Samus comes out victorious yet again, and watches as the lava beast sinks into its natural habitat, never to be seen again.
Metroid Prime 3: Corruption