Sight and Smell - The Eyes and Nostrils A salmon's eyes help it seek food, avoid predators and perhaps navigate in the ocean. Like all fish that are bathed constantly in water, salmon do not need eyelids. Fish use their nostrils only for smelling, their gills look after the breathing function. Salmon have a keen sense of smell far more acute than a dog's and are thought to use it in finding their home streams for spawning.

Touching and Hearing - The Lateral Line Fish use the "lateral line," a system of small holes along the sides of their bodies to detect sounds in the water and find their way in dark or muddy conditions. The line is connected to a delicate system of nerves, and emits sonar-like vibrations.

Breathing - The Gills Like all fish, salmon breathe through their gills. Thin membranes of blood-filled laminae, or branches of the gills, functioning much like alveoli in human lungs, transfer carbon dioxide from the body and absorb oxygen from the water. Sharp-spined gill rakers prevent food from entering the gill passages, and gill covers (operculi) protect the delicate gill filaments. Water is taken in through the mouth and forced out over the gills. Cold water saturated with oxygen has only 13 parts of oxygen for every million parts of water.

Feeding - The Mouth Fish use their mouth to catch food, but do not chew before swallowing. The mouth is also part of the breathing process, constantly drawing in water and forced it out over the gills.

Swimming - The Fins and Scales Salmon have two sets of paired fins (pelvic and pectoral) and four single fins (dorsal, caudal, anal and adipose). All but the adipose and caudal fins are used to balance the fish. The small, fleshy adipose fin has no known purpose, but the caudal (tail) fin acts like a rudder. Combined with the propulsive power of the salmon's muscular body, the caudal fin steers the fish through the water. It is also used by the female salmon to dig the nests in which she lays her eggs.

Salmon are protected by the scales which cover their bodies in concentric patterns, as well as by the slimy layer of mucous that discourages disease organisms and helps it slide through the water. Scales, made of blood vessels, nerves and connective tissue, grow larger and harder as the maturing salmon enters the seawater environment, but do not change in number. Scale patterns and marks (annuli) are used to identify the species of a salmon, and also to determine the age of the fish, revealing how many years a salmon has spent at sea and the number of times it has spawned.