An operculum covers and protects the gills.
Step-by-step explanation:
An operculum is a flexible bony type of plate which protects the sensitive gills. When water is inhaled through the mouth it moves over the gills and is exhaled from below the operculum ( gill cover). gills remove oxygen that is present in the water and diffuse carbon dioxide from fish's body. Some fishes have spines which are located on the opiculum( gill cover) which acts as a defense mechanism to secure them from the predators.