Function of operculum

operculum ( plural ; operculi ) is actually gill cover or lid of a cavity having gills . its major function is to protect gills as well as to move water over gills so that gill may be able to extract oxygen from water . as this lid play an important role in moving water over gills so fishes having operculum can survive even if they are stationary . on other hand fishes lacking operculi have to move continuously to survive .

all bony fishes have operculi . best example of fish having no operculum is shark.