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Salmon

Water Pollution, Fishing, And Fish-farming



Because of their migratory habits and abundance, salmon have a long history of being a valuable source of food for people. In fact, before water pollution became a major problem, these fish were cheap and easy to get. However, with the onset of the industrial revolution, many rivers became polluted or were blocked by dams, and salmon populations declined or disappeared. Furthermore, decreases in salmon populations were intensified by increased fishing in salmon feeding habitat at sea. Fishery biologists are attempting to stem the salmon declines by enhancing wild stocks, for example, by releasing large numbers of captive-reared, young fish. This so-called "stock enhancement" can help, but it is also necessary to stop or repair the damage to aquatic habitat, and control the rate of fishing.



As a result of their decline, salmon became a high priced luxury item. Subsequently, the industry of fish farming arose, introducing the practice of rearing salmon in cages in embayments or at sea, or in ponds on land. The most popular species of salmon being farmed are Atlantic salmon, rainbow trout, Coho salmon, pink salmon, and American brook trout. Fish farming has helped to offset some of the decreases in salmon populations. However, other important problems have developed, because of chemicals used to prevent diseases in captive salmon and the build-up of organic sludge beneath fish-cages. Until measures are taken to control water pollution and to stop overfishing, salmon populations will not be able to return to their once abundant numbers.


Resources

Books

Drummond, Stephen Sedwick. The Salmon Handbook. London: Robert Hartnoll, 1982.

Nelson, Joseph S. Fishes of the World. 3rd ed. New York: Wiley, 1994.

Whiteman, Kate. World Encyclopedia of Fish & Shellfish. New York: Lorenz Books, 2000.


Kathryn Snavely

KEY TERMS


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Adipose fin

—A small, extra dorsal fin located well back on the fish's spine in front of the tail.

Alevin stage

—The time in a salmon's life right after it hatches when it feeds on its yolk sac.

Anal fin

—The fin located on the belly just before the tail fin.

Caudal fin

—The tail fin of a fish.

Dorsal fin

—A fin located on the back of a fish.

Fry

—Follows the alevin stage, when the young fry leaves the gravel and feeds on invertebrates.

Kelts

—Atlantic salmon that have lived through their spawning, and try to return to sea. They may spawn again the following year.

Kype

—The hooked lower jaw of a male Atlantic salmon, grown when spawning to fight other males.

Parrs

—The name for salmon when they have grown around an inch or so long and become camouflaged by dark splotches on their body.

Pectoral fins

—The first two fins on the fish's lower sides, almost to its belly.

Pelvic fin

—Located on the fish's belly, slightly to the rear of the dorsal fin and in front of the anal fin.

Redd

—A shallow nest dug by the female prior to spawning.

Smolts

—When the salmon grows 4–7.5 in (10–18 cm) long, it loses its splotches, becomes silver colored, and migrates to sea.

Additional topics

Science EncyclopediaScience & Philosophy: Revaluation of values: to Sarin Gas - History And Global Production Of SarinSalmon - Atlantic Salmon (salmo Salar), Pacific Salmon (oncorhynchus Species), Water Pollution, Fishing, And Fish-farming