The anatomy of bony fish share many characteristics with other vertebrate. As you look at a diagram showing the internal organs of a typical bony fish, how many of these organs look familiar? How many do humans also have?
The Digestive Tract (back to top)
Depending on habitat (the place where the fish lives) and the innate preferences designed by evolutionary adaptation (to survive in a particular habitat one species of fish might eat plants, while another might eat shell fish. In this way, both species can survive in the same habitat) fish have numerous modes of feeding. Some fish are herbivores, eating only plants. Others are carnivores, eating meat. Still others are omnivores and consume plants and meat. Pacific Salmon are omnivores. They eat smaller fish, crustaceans, and insects.
When eating, food enters the digestive tract through the mouth. From the mouth, the food passes through a short tube called the esophagus to the stomach, which partially breaks down the food. From the stomach food passes through an organ humans do not have. This organ is called the pyloric ceca, a series of finger-like ouches. It is located were the stomach and intestine meet. Through the secretion of enzymes the pyloric ceca breaks down the food further and absorbs nutrients. The intestine completes the digestive process. The liver and pancreas secrete digestive enzymes to the intestine. (An interesting note: Herbivores tend to have longer intestines than carnivores. This is true of most animals.) Materials that pass the intestine undigested are eliminated through the anus.
Respiratory and Circulatory Systems (back to top)
The respiratory system of trout and salmon differs greatly from land animals. Check out this diagram. What organs are unique to fish?
The circulatory system of trout and salmon, all bony fish, share characteristics common to many other animals. Some characteristics are unique. Check out this diagram. What organs are unique to fish? What organs and processes do fist share with other animals?
Most fish, including trout and salmon, breathe through gills located on either side of the pharynx. The gills are feathery filaments containing many capillaries and a large surface area for the exchange of oxygen and carbon dioxide. Trout and salmon breathe through the mouth, pumping water the gill filaments. They exhale through a single opening, the gill slits, which is protected by a gill cover.
Like most complex animals, fish have a closed circulatory system with a heart that pumps blood through the body. The heart consists to two muscular chambers that pump the blood: An atrium and a ventricle. Blood from the body gathers in the atrium, which is then pumped into the ventricle. The ventricle pumps the blood into a muscular vessel called the aorta. Blood goes directly from the aorta to the fine capillary network in the gills, where the exchange of gas takes place. From the gills, the blood travels throughout the body providing tissue and organs with life giving oxygen and removing carbon dioxide. Once the blood has completed its journey through the body, it gathers in a thin-walled sac called the sinus venosus before entering the atrium once again.
Excretion (back to top)
Fish get rid of nitrogenous wastes in the form of ammonia. Some wastes diffuse through the gills. Others leave through the kidneys. The kidneys are composed of many tubules that filter nitrous wastes from the blood and concentrate them. Kidneys also help fish control the amount of water in their bodies. Fish who live in the salty environment of the oceans tend to loose water through osmosis. The salt pulls the liquid from the body. Kidneys in ocean dwelling fish work to concentrate the wastes so as to return as much water as possible to the body. The kidneys of fresh water fish dilute the urine and pumps out as much water as possible. In fresh water, a great deal of water enters the body through osmosis. Salmon, because they are able to move between fresh water and ocean environments, have the ability to control kidney function.
The Nervous System (back to top)
The nervous system of trout and salmon, all bony fish, share characteristics common to many other animals. Some characteristics are unique. Check out this diagram. What makes the nervous system of fish unique? Similar?
Fish have highly developed nervous systems organized around a brain. Fish brains have several clearly visible parts.
The most anterior parts of a fish's brain are the olfactory bulbs. These are connected to the two lobes of the cerebrum by stalks. In fish the cerebrum is primarily involved with the sense of smell. It also seems to control behaviors such as taking care of the young and exploring the environment. The optic lobes process information from the eyes. The cerebellum coordinates body movements and the medulla controls internal organ functions and maintains balance.
Posterior to the brain is the spinal cord, which is the hollow dorsal nerve cord that characterizes chordates. The spinal cord is enclosed and protected by the vertebral column. Between each set of vertebrae, a pair of spinal nerves exits the cord and connects to the internal organs and muscles.
Most fish have superbly designed sense organs. Fish like trout and salmon, which are active in the daylight, have well-developed eyes and color vision nearly equal to the average human. They also have extraordinary senses of taste and smell. Chemo receptors (chemo-means chemical) are located all over the head and much of the body surface. Salmon can distinguish between the odor of their own home stream and that of another stream while they are still far out at sea. Most fish have ears inside their heads, but they do not hear well. However, a series of pores connected to canals beneath the skin cover the head and the sides of their body. This system, called the lateral line system, detects the motion. Some fish-electric eels, catfish, and sharks-can detect electricity.
Reproduction (back to top)
Fish are separated into males and females. A number of fishes, however, are born males, but change into females; or are born females and change into males.
Many fish, including trout and salmon, are oviparous. This means they lay eggs. Sharks and rays have internal fertilization and lay fertilized eggs. Most fish, including trout and salmon, lay unfertilized eggs. The eggs are fertilized externally by the male. Fish typically release hundred or even millions of eggs, which increases the chance that a few offspring will survive into adulthood.
Although usually drab in color before the breeding season, which varies with the species, members of the salmon family develop bright hues at spawning time. The male, during this season, usually develops a hooked snout and a humped back. Before mating, one parent excavates a nest for the eggs; after the eggs are deposited and fertilized, the female stirs up the stream bottom so that earth and stones cover the eggs and protect them. The eggs hatch in two weeks to six months, depending on the species and the water temperature. During the migrations and nest-building activity proceeding mating, neither the females nor the males consume food.
The Atlantic salmon migrates to cold, fresh water in late spring or early summer, swimming upstream at an average rate of up to 6.4 km (4 mi.) per day. Because salmon can jump as much as 3.7 m (12 ft) out of water, they clear most obstacles in their path. The female lays as many as 20,000 eggs in October or November, after which time the adult salmon float downstream and return to the sea. Unlike the various species of Pacific salmon, the Atlantic salmon does not die after its first spawning but returns year after year to its breeding place. The newly hatched young, known as parrs or brandlings because of the dark transverse markings on their sides, remain in fresh water for about two years. At this time, the young, known as smolts, become silvery in color and descend to the sea. Upon the first return of the Atlantic salmon to its spawning ground, the fish is known as a grilse. After spawning, it is known as a kelt.
Salmon found in the North Pacific Ocean spawn only once, dying after depositing and fertilizing their eggs. The Chinook salmon migrates farther than any other salmon, often traveling 1600 to 3200 km (1000 to 2000 mi.) inland to its spawning ground. Its eggs usually hatch within two months, and the young descend to the sea when 5 to 7.5 cm (2 to 3 in) long.
Reproduction in Hatcheries (back to top)
To mitigate the decimation of wild salmon runs caused by construction of dams and over fishing, the U.S. Fish and Wildlife Service yearly deposits billions of salmon eggs and young, propagated in nurseries, into natural breeding grounds and constructs fish ladders for the upstream journey of mature salmon. However, hatchery-raised salmon have aggressive feeding habits. This means, unlike wild salmon that spend most of their time in deep water or under cover, hatchery raised salmon spend most of their time at the water's surface looking for food . As a result, hatchery-raised salmon consume most of the food wild salmon need to live. At the same time, this aggressive feeding makes hatchery salmon more vulnerable to predators because they stay near the surface. Hatchery salmon usually have less genetic diversity than wild salmon. This can lead to lowered resistance to disease and other environmental hazards.
Kinds of Salmon (back to top)
Scientific classification: Salmon belong to the family Salmonidae.
Salmon (fish), common name applied to fish characterized by an elongate body covered with small cycloid (rounded, with smooth edges) scales and possessing an adipose (fleshy) fin between the dorsal fin and tail. These fish belong to the salmon family. Most members of this family are valuable food fish and excellent game fish. They are found in both fresh and salt water in the colder regions of the northern hemisphere. Many return from salt water to fresh water to breed, and the young migrate to salt water from fresh water after they reach maturity. The migratory instinct of members of the salmon family is remarkably specific, each generation returning to spawn in exactly the same breeding places as the generation before it. Even those species that do not migrate from fresh water to salt water spawn in the same freshwater streams as did their ancestors. The spawning ground of these fish is usually a rapidly flowing, clear stream with gravel and rocks on the bottom.
Atlantic Salmon (back to top)
Scientific classification: The Atlantic salmon is a member of the family Salmonidae in the Salmoniformes order. It is classified as Salmo salar.
Atlantic Salmon, commercially valuable member of the salmon family that lays its eggs, or spawns, in freshwater streams on both sides of the Atlantic Ocean, then migrates to sea. Though its life history and appearance are similar to species of salmon in the Pacific Ocean, the Atlantic salmon is actually more closely related to the brown trout.
Atlantic salmon historically ranged from Portugal north to Greenland and south to the Eastern United States. Attempts to introduce Atlantic salmon to other places around the world have failed, except in landlocked lakes in Argentina and the western United States and Canada.
Average adult fish weigh 3.6 to 5.5 kg (8 to 12 lb) and reach about 75 cm (30 in) in length, but Atlantic salmon can obtain weights of up to 38 kg (84 lb) and lengths of almost 1.5 m (5 ft). At sea, the fish are blue-black with silver undersides. As they approach freshwater to spawn they turn red, sometimes almost black, and males develop an exaggerated upper jaw in preparation for fighting over females.
Unlike salmon species of the Pacific that spawn once and die, Atlantic salmon spawn over several successive years. Fish may swim more than 1600 km (more than 1000 mi) back to their streams of origin. During the spawning season in the late fall or early winter, a female digs a nest, called a redd, by turning over on her side and vigorously excavating the gravel streambed with powerful strokes of her tail. Males fight for the opportunity to spawn with females. As the female deposits an average of 5500 to 9500 eggs into the nest, a male sprays milt (sperm) over them. The female covers the nest with additional gravel to protect the eggs. Then both parents swim back to sea, leaving the eggs to hatch on their own.
When the larval fish hatch they stay hidden in the gravel, nourished by a yolk sack attached to their bodies. When the yolk is absorbed, the fish emerge from the gravel and begin feeding. The young feed on insects and insect larvae in rivers. As the fish migrate to sea they switch to a diet of progressively larger fish. Atlantic salmon stop feeding temporarily when they return to freshwater to spawn, surviving instead on reserves of fat and protein.
Most native Atlantic salmon populations are declining in number or gone due to over fishing and habitat destruction. Wild populations have fallen to less than a quarter of what they were twenty years ago. In the United States, the last remaining stocks are found in Maine. A proposal to list Atlantic salmon as an endangered species under the Endangered Species Act was withdrawn in late 1997 in favor of a conservation plan proposed by the state of Maine. Efforts to restore wild salmon runs south of Maine have been unsuccessful.
Atlantic salmon are raised commercially in net pens in Norway and on the west coast of North and South America. These salmon are sometimes referred to as farm-raised salmon. On the west coast of the Pacific, there is the danger that if any Atlantic salmon escape from the pens, they may take over the habitat of native Pacific salmon.
"Atlantic Salmon," Microsoft¨ Encarta¨ Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved.
Pacific Salmon (back to top)
Scientific classification: Pacific salmon belong to the genus Oncorhynchus. The Chinook salmon is classified as Oncorhynchus tshawytscha, the sockeye salmon as Oncorhynchus nerka, and the Coho salmon as Oncorhynchus kisutch.
The best-known and most valuable species is the Chinook salmon, which is also known as the king salmon, Columbia River salmon, quinnat, chowichee, and takou. Market specimens of this fish average about 9 kg (about 20 lb) in weight, but numerous specimens more than 1.5 m (more than 5 ft) in length and well over 45 kg (more than 100 lb) in weight have been recorded.
The Chinook salmon migrates farther than any other salmon, often traveling 1600 to 3200 km (1000 to 2000 mi) inland to its spawning ground. Its eggs usually hatch within two months, and the young descend to the sea when they are 5 to 7.5 cm (2 to 3 in) long. The sockeye, red, or blue-black salmon is another valuable species, as is the Coho, or silver salmon, which has light pink flesh.
Other salmon in the Pacific Basin are commonly known as the pink salmon, or humpback salmon, and the chum salmon, or dog salmon.
The Economics of Salmon (back to top)
Anglers fish for salmon with rod and reel, usually using flies as bait. Commercial fishing for salmon is done on a much larger scale, employing traps and pound nets to catch the fish on the way to their spawning grounds. The salmon fishing industry is one of the major industries of the American Pacific coast, providing 60,000 jobs and more than $1 billion in income per year for the region.
The annual harvest of wild and farm-raised salmon in the United States averages about 478,000 metric tons, of which about 60 percent is canned.
Conservation Issues (back to top)
Though the U.S. Fish and Wildlife Service deposits billions of salmon eggs and young, propagated in nurseries, into natural breeding grounds and constructs fish ladders for the upstream journey of mature salmon, wild Atlantic and Pacific salmon populations remain severely threatened. In particular, the drastic decline of wild Pacific salmon populations has raised alarm and become one of the most important conservation issues in the Pacific Northwest.
Less than 2 percent of the wild salmon population of the Columbia River Basin (including parts of Washington, Oregon, Idaho, Montana, Wyoming, and British Columbia) remains and only one individual sockeye salmon returned to the Snake River in Idaho in 1994.
Coho salmon in the Snake River have been declared extinct by the U.S. Fish and Wildlife Service, as have 106 other salmon populations on the West Coast.
The causes of this dramatic decline include the construction of dams, which interfere with both upstream and downstream migration of the fish-15 to 30 percent of young salmon die at each dam as they migrate down river; loss of spawning habitat due to development; and logging and agriculture near waterways, which lead to erosion, siltation (the clouding of waterways with fine soil), toxic runoff, and high water temperatures, all of which interfere with salmon spawning and migration.
The decline of salmon populations is uniting environmentalists and fishers with industries that extract natural resources, such as hydroelectricity, timber, and water, to find a compromise that saves both the wild salmon populations and the fishing industries that depend on the species' continued health. Efforts to protect salmon populations in the Pacific Northwest include barging or trucking young salmon around dams; reducing industrial and agricultural water withdrawals from river systems; prohibiting logging near streams or rivers; dramatically limiting salmon fishing seasons; and increasing water flow, or spillage, through hydroelectric dams.
"Salmon (fish)," Microsoft¨ Encarta¨ Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved.
Conservation Organizations
Resources (back to top)
Microsoft¨ Encarta¨ Encyclopedia 99. © 1993-1998 Microsoft Corporation
Check out your Independent Bookseller for:
Books About Salmon
Adopt-A-Stream Foundation and Robert Steelquist. Field Guide to the Pacific Salmon (Adopt-A-Stream Foundation). Sasquatch Books, 1992.
Atkinson, R. Valentine and Nick Lyons. Trout and Salmon. Lyons Press, 1999
Clarke, W. C. ed. Physiological Ecology of Pacific Salmon. University of British Columbia, 1995.
Cole, Joanna, et al.Magic School Bus Goes Upstream : A Book About Salmon on Migration (Magic School Bus Series). Scholastic Trade, 1997. (Suitable for children)
Committee on Protection and Management of Pacific Northwest anadromous. Upstream : Salmon and Society in the Pacific Northwest. National Academy Press, 1996.
Cone, Joseph. A Common Fate : Endangered Salmon and the People of the Pacific Northwest. Oregon State University Press, 1996.
Cone, Molly. Come Back, Salmon : How a Group of Dedicated Kids Adopted Pigeon Creek and Brought It Back to Life. New York: Scholastic, Inc., 1992. (Suitable for Children)
Groot, G. and L. Margolis, eds. Pacific Salmon: Life Histories. University of British Columbia, 1991.
Haig-Brown, Roderick L. and et. al. Return to the River : The Classic Story of the Chinook Run and the Men Who Fish It. Linden Publishing, 1997.
Pearcy, William G. Ocean Ecology of North Pacific Salmonids (Books in Recruitment Fishery Oceanography). Washington Sea Grant Program, 1992.
Roche, Judith and Meg McHutchison, eds. First Fish, First People: Salmon Tales of the North Pacific Rim. University of Washington Press, 1998.
Shearer, W. M. The Atlantic Salmon : Natural History, Exploitation and Future Management The Atlantic Salmon : Natural History, Exploitation and Future Management. John Wiley and Sons, 1992.
Books About Fish
Cailliet, Gregor and others. Fishes. Wadsworth, 1986. "A Field and Laboratory Manual of Their Structure and Natural History" (titlepage).
Dalrymple, Byron. Complete Guide to Game Fish. Van Nostrand, 1981. "A Field Book of Fresh and Saltwater Species" (titlepage).
Goode, G. Brown. Game Fishes of the United States. Winchester, 1973. Comprehensive, well-illustrated descriptions; first published 1879.
Herald, Earl S. Living Fishes of the World. Doubleday, 1961, 1975. Emphasis on less popular fish; arranged by species, then structure.
McClane, A. J., ed. McClane's Field Guide to Freshwater Fishes of North America. Holt, 1978. Arranged by popular name. Companion: McClane's Field Guide to Saltwater Fishes of North America.
Nelson, Joseph S. Fishes of the World. Wiley, 2d ed., 1984. Classic classification.
Ommanney, F. D. and others. The Fishes. Time-Life, 1970, 1977. Superior illustrations, appendixes of facts, and text on fish biology and commercial use.
Robins, C. Richard and G. Carleton Ray. A Field Guide to the Atlantic Coast Fishes of North America. Houghton, 1986. Covers 1000 species. Excellent companion to: A Field Guide to Pacific Coast Fishes of North America (1983).
Books About Fishing
The Compleat Freshwater Fisherman. Prentice, 1987. From species and locations to equipment and cleaning the catch.
Fisher, Jeffrey A. The Fish Book. Emerson, 1981. Basic information, buying gear to cooking.
Goddard, John and Clarke, Brian. The Trout and the Fly: A New Approach. Doubleday, 1980. Winchester, 1984. "Fish-eye view" of casting patterns, lures, rods.
Hersey, John. Blues. Knopf, 1987. On fishing off Martha's Vineyard-and life.
McClane, A. J., ed. McClane's New Standard Fishing Encyclopedia and International Angling Guide. Holt, 1965; rev., 1974. A dictionary; bibliography.
Walton, Izaak. The Compleat Angler. Various publishers. Classic tale of five days' fishing; first published 1577. "Further Reading Subtopics,"
Books About Fisheries
Browning, Robert J. Fisheries of the North Pacific. Alaska Northwest, 1980. On history, gear, processes.
Meltzer, Michael. The World of the Small Commercial Fishermen: Their Lives and Their Boats. Dover, 1980. P. Smith, n.d. Canning, ethnic fishing groups, east and west coasts of the U.S.
Warner, William W. Distant Water. Little, 1983. "The fate of the North Atlantic fisherman" (titlepage).
Microsoft¨ Encarta¨ Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved.
Water makes up more than 76 percent of the Earth's surface. Barring ecological degradation, wherever you find water you will find fish. Therefore, no one should be surprised to learn that life first appeared in the oceans and seas and that the first vertebrae were jawless fishlike animals called ostracoderms because external body plates made of a material similar to bone covered their bodies. (Ostraco comes from the Greek word osteon, which mean bone. Derm also comes from a Greek word, derma, which means skin.) These early ancestors flourish about 540 million years ago during a period scientists call the late Cambrian Period. About 100 million years later, during the Ordovician and Silurian periods, these fish underwent major physiological changes. Some of these new fish were jawless fish, but with less body armor. Most of these fish ultimately became extinct during the Devonian Period about 350 million years ago. A few descendants remain of these ancient fish: the 