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
Fish have a specialized organ called the swim bladder, which allows them to regulate their buoyancy. By adjusting the amount of gas in the swim bladder, fish can control their density relative to the surrounding water, enabling them to maintain their position in the water column without sinking or rising excessively. This adaptation helps them conserve energy while swimming and aids in navigating their aquatic environment.
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.
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
Without fins, fish would not be able to move around (swim) and live.