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Body Parts That Help the Fish Move in the Water

Fish have evolved to take full advantage of their environment and have many body parts that enable them to swim. Using a variety of internal organs and external body features, fish display an incredible ability to move through water. Body structure, fins, tail, muscles and swim bladder all work together to allow these creatures to exhibit movement that is perfectly attuned to their habitat.

Muscles and Tail
- The body of a fish can contain up to 80 percent muscle. These muscles provide the power that enable the fish to propel itself through its environment of dense water. Muscles are arranged in multiple ways to allow the fish to move in any direction. Muscle contraction pushes the fish's body forward and through the water. Its tail, also known as the caudal fin, is the main propelling fin and can be shaped differently to provide a variety of swimming characteristics. Rounded tails lend themselves to slower swimming with crescent and fork shaped tails more suited to faster movement.
Fins
- Sharks have distinctive dorsal fins.
  
  Fish have number of different types of fins that perform various functions related to swimming. The caudal fin, or tail, is the main propelling fin. The dorsal fin is located on the fish's back and is critical to providing stability and controlling roll from side to side. Pectoral fins are located on the sides near the front portion and are used as brakes by creating drag while assisting in side to side movement. The pectoral fins are also used with the pelvic fins to enable a fish to swim in an up and down direction. Other fins such as the anal, adipose and ventral fins assist in providing additional stability while swimming.
Swim Bladder
- Swim bladders are used to provide buoyancy to a fish. It is a sac inside the fish's abdomen that is filled with gas. This gas is predominately oxygen with some nitrogen and carbon dioxide also present. Fish with damaged swim bladders cannot maintain their upright position in the water. Home aquarium enthusiasts may be familiar with fish losing control of their ability to properly swim. This is often caused by a damaged swim bladder.
Body structure
- Reef fish often have a compressed shape
  
  A fish's body structure is an important determining factor in its swimming characteristics and are tailored to its specific environment and habits. Tuna, which school in open waters, are torpedo-shaped to allow for high speed swimming. Catfish are generally shaped like a horizontal disk which helps them stay on the bottom. Reef fish often exhibit a compressed shape which enables them to be very agile and use sudden bursts of speed when required.

Animals & Science