The original award-winning NEFSC FishFAQ, created in 1993, has been archived.
For current information, please see our new FAQ.

Do fish
breathe air?

Yes, but not directly into the lungs as mammals do (except for some tropical fish). (Actually they breathe oxygen not air.) As water passes over a system of extremely fine gill membranes, fish absorb the water's oxygen content. Gills contain a network of fine blood vessels (capillaries) that take up the oxygen and diffuse it through the membranes.

How do fish swim? How fast?

Primarily by contracting bands of muscles in sequence on alternate sides of the body so that the tail is whipped very rapidly from side to side in a sculling motion. Vertical fins are used mainly for stabilization. Paired pectoral and pelvic fins are used primarily for stability when a fish hovers, but sometimes may be used to aid rapid forward motion.
Tunas and tuna-like fish, billfish, and certain sharks are the speed champions, reaching 50 miles per hour in short bursts. Sustained swimming speeds generally range from about 5 to 10 miles per hour among strong swimmers.

Can fish swim backwards?

A number can, but usually don't. Those that can are mostly members of one of the eel families.
moray eel
Moray Eel

Do all fish swim in the horizontal position?

seahorse Most do. The sea horse is among the exceptions. Another is the shrimp fish of the Indian Ocean, which congregates in schools of several individuals and swims vertically, its long tube-like snout pointing directly upward. A catfish indigenous to the Nile and other African rivers also swims in the vertical posture. Many kinds of midwater deepsea fishes swim or rest vertically.

Do fish chew their food?

Not in the human manner. Carnivorous fish like sharks use their sharp teeth to seize and hold prey while swallowing it whole or in large pieces. Bottom dwellers such as rays are equipped with large flat teeth that crush the shellfish they consume. Herbivorous fish (grazers) often lack jaw teeth, but have tooth-like grinding mills in their throats, called pharyngeal teeth. Fish would suffocate if they tried to chew, for chewing would interfere with the passage of water over the gills, necessary for obtaining oxygen.

Tuna image courtesy of "Regulatory Fish Encyclopedia, Office of Seafood and Office of Regulatory Affairs, Food and Drug Administration, 1993-1996."

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