A tagging study of Ocean Sunfish (Mola mola) in the Northwest Atlantic, recorded a sunfish reaching a maximum depth of 844m.
Reference: Potter & Howell (2011)
Ocean sunfish exhibit daily vertical movement, visiting deeper depths numerous times during the day, with warm-up breaks in between at or near the surface. At night they tend to remain in shallower waters.
Reference: Dewar et al. (2010)