Swimming: How Does a Fish Swim?

Anatomy of a FishWhile watching your pet fish swimming around in their watery home, you may find yourself wondering how they seem to swim so easily. Their skeletons and muscles work together to allow them to swim, along with their fins and something called a swim bladder.

Using the Skeleton and MusclesThe primary function of the skeleton is to aide movement of other parts. The skull is the only truly fixed part of a fish. It does not move in and of itself but acts as a point of stability for other bones. These other bones act as levers that cause movement of the fish’s body. While the bones provide the movement, the muscles supply the power. A typical fish has hundreds of muscles running in all directions around its body. This is why a fish can turn and twist and change directions quickly.

Using the FinsAs water passes over its body, a fish uses its fins to thrust in the direction it wishes to go. The caudal fins supply most of the thrust. The pelvic, dorsal and pectorals assist in side to side movement and lift the body.

The Swim BladderA swim bladder in the belly of the fish fills with gas and expands or deflates according to the depth of the surrounding water. This enables the fish to swim without floating upward or sinking unexpectedly. The fish bladder is sort of like the fishing bobber on a fish line.The bobber keeps the fishhook at the desired level without sinking or coming to the surface. The swim bladder does the same thing for the fish. Sometimes the swim bladder malfunctions. If this happens, a fish is not able to swim correctly and may start swimming upside down. If a pet fish does this, contact your veterinarian right away.

Fish ScalesThe last thing that helps a fish swim through the water is an oily discharge that covers the body and scales. Fish skin is made of tiny overlapping scales. The oil on the scales causes the water to glide easily over the fish.

Types of SwimmersThere are two kinds of swimmers in the fish world. A cruiser swims constantly, looking for food. A burst fish tends to swim in small bursts and hide in between bursts. Both kinds of swimmers use the process described here to swim.