Identify the fish that has four pairs of gills which are covered by an operculum on each side.
Class Osteichthyes includes bony fishes (e.g., Exocoetus - flying fish). They have four pairs of gills which are covered by an operculum on each side.
Scoliodon belongs to Chondricthyes. It has five pairs of gill slits.
Petromyzon is a cyclostome with 6-15 pairs of gill slits.
Ichthyophis belongs to amphibians