Many ocean fish spend their larval stages floating with the plankton in the open sea. And many of these organisms carry out a daily migration, sinking into the depths during the day and rising toward the surface at night to feed. Taking pictures of them is an "emerging hobby" called blackwater photography. Above, larval lionfish, about an inch (2.5 cm) long, by Steven Kovacs.
Bony-eared assfish. (So far as I can tell, not an April Fool's joke)