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FISH HAVE A LATERAL LINE This line that runs along each side of the fi sh is actually a series of holes. The holes connect to nerves inside the fi sh that are sensitive to vibrations and water movements. This makes fi sh highly aware of its surroundings. FISH PRODUCE MUCOUS They wear a coat of slime that covers their bodies. This reduces friction in the water, allowing fi sh to move easily in water without expending much energy. Another important function of the slime coat is to protect the fi sh from disease and parasites. FISH HAVE A SWIM BLADDER The swim bladder helps a fi sh to stay suspended in the water. It is a gas fi lled chamber, and fi sh can adjust the amount of gas in the bladder until their density equals the density of the water. The swim bladder allows a fi sh to be neutrally buoyant. This also functions to help the fi sh reserve energy for other important activities like foraging for food or reproduction. FISH ARE COLD BLOODED A fi sh can't control its body temperature. Instead, internal temperature is determined by the temperature of the water a fi sh lives in. Some fi sh like the rainbow trout can only live in cool or cold water; others like the channel catfi sh, largemouth bass or bluegill are considered warmwater fi sh. ADDITIONAL ANATOMY FEATURES: Eyes A fi sh's eyes are placed on the sides of the head, allowing it see in almost all directions except directly behind or underneath, although predator fi sh often have eyes that are located further forward on their heads. This provides them with better depth perception to pursue and catch their prey. Large eyes can help fi sh see well in the dark or in murky water. Light doesn't travel very far underwater, so even fi sh in clear water can't see great distances. (Because sound travels much faster and further in water, fi sh have adaptations that make them very sensitive to sound.) Like humans, fi sh can see colors and brightness, but many fi sh don't see a full range of color. Unlike humans, fi sh don't have eyelids and their pupils are fi xed; they are always the same size regardless of the amount of light there is. Often, fi sh will spend bright sunny days in deep water or in the shade.. C. IVERSON, MINNESOTA DEPARTMENT OF NATURAL RESOURCES C. IVERSON, MINNESOTA DEPARTMENT OF NATURAL RESOURCES 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 CHAPTER 6 ● FISH ANATOMY