Ghost Fish

[Garlicfield]

Where do you find the ghostfish in Stardew valley, what pool of water is more likely to spawn it?

[vernicom]

Floor 20 in the mines.

[Tumas Altaawus]

Floor 20 or 60 of the mines (and 40 if there's a pool there), as well as killing ghosts.

[Bastycore]

Ghostfish spawn at mine level 20, 60 and 100 in the water pools.