Because they are underwater. They have to get oxygen that is dissolved in the water instead of that available in the air. Fish have an air bladder which controls their buoyancy. Some fish can use it as a lung. When they swim in the water they use their gills. When they are on land, they use their lung.
Fish Use Gills Instead of lungs. Gills Help fish to Breath. Fish Use Gills Instead of lungs. Gills Help fish to Breath.
the fish has gills
Fish use gills to extract oxygen from the water passing over the gills.
amphibians use gills AND lungs, fish/marine life use gills alone
Fish use gills to breathe underwater.
A fish! Fish are the only animals with gills and most live in water.
to breath
Oysters have gills. They absorb oxygen from the water.
All fish breathe through their gills. Some have additional organs to assist but all fish use their gills to obtain oxygen from the water they live in.
Fish have internal gills.Gills covered with operculumn except in sharks and rays.They have opened gills
Gills are an organ that fish have, that enables them to obtain oxygen from the water that they are in; it is what fish use instead of lungs.
holes that fish use to breath