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., Labeo - rohu). 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 the class Amphibia.