The fish that live at the bottom of the sea are equiped with a swim bladder and by adjusting the pressure in this organ they can go up or down easily as they swim.
enables the fish to maintain its depth without floating upward or sinking.
They can breathe underwater because they have gills. They also have fins so they can swim underwater without sinking.
Fish do not normally "float around" they swim. If your fish is floating/sinking then it is probably dead.
They can breathe underwater because they have gills. They also have fins so they can swim underwater without sinking.
The swim bladder
It is called the "Swim Bladder".
Fish have an gas-filled, internal swim bladder, whose buoyancy they regulate to keep from sinking or rising in the water.
Fish body is of boat shape to balance itself in the water nature have given swimming bladders for fish.
Without fins, fish would not be able to move around (swim) and live.
One adaptation would be a swim bladder, that being in bony fish. Sharks I believe have their liver that excretes squalene, which I believe has something to do with their density. In fact, it does.
Shark
swim bladder is what helps the fish stay afloat without the swim bladder a fish would simply sink duhhh