Salmoniformes

(vertebrate zoology) An order of soft-rayed fishes comprising salmon and their allies; the stem group from which most higher teleostean fishes evolved.

(Salmons)

Class: Actinopterygii

Order: Salmoniformes

Number of families 1

Evolution and systematics

Salmoniform fossils are known from the Upper Cretaceous (about 100 million years ago) until the Pleistocene (about 11,000 years ago), mostly from North America and Europe. This order possesses several primitive anatomical features representative of an early stage in the evolution of modern bony fishes. There have been a number of systematic arrangements for this group, ranging from a single order with a single family (Salmonidae), to two orders with several families (see, for example, Johnson and Patterson 1996). For the purpose of this chapter, we will follow Nelson (1994), who considers the Salmonidae the only family for this order, with 3 subfamilies, 11 genera, and 66 species.

Physical characteristics

The largest of the salmoniform fishes are the Chinook salmon (Oncorhynchus tshawytscha) and the Danube and Siberian huchens (Hucho hucho) both about 59 in (1.5 m) in length, with the former weighing up to 136 lb (62 kg). As expected from such strong swimmers, the salmoniform body and fins are streamlined and symmetrical, being covered with small and smooth cycloid scales. All fins have soft rays. They have a small, fleshy adipose fin (which is a primitive character) located between the dorsal fin and the powerful caudal fin. The dorsal fin is located midway along the body; the paired pectoral fins are ventral and located directly posterior to the head. They also have a pair of pelvic fins directly beneath the dorsal fin, and a single anal fin located beneath the adipose fin. The swim bladder is connected to the gut.

Distribution

Salmoniformes were originally found only in cool and cold waters of the Northern Hemisphere, where they are one of the most dominant freshwater fishes. In the North American continent, they are found from tributaries of the Arctic Ocean to tributaries of the Gulf of California in northwestern Mexico. They are also found from Eurasia to all Asia north to the Himalayas from the Arctic Circle south to Bangladesh, Manchuria, and the Korean Peninsula and the Japanese Islands and Taiwan. In Africa they are only found in the northwestern margin (Atlas mountains of Morocco and Algeria). The Arctic char (Salvelinus alpinus) is the world's most northerly occurring freshwater fish. Many species of this order have been successfully introduced in many other parts of the world.

Habitat

Many salmoniform species (such as trouts and salmons) have an anadromous life cycle, in that they spawn in fresh waters, but migrate to sea for feeding and maturation. The pink salmon (Oncorhynchus gorbuscha) is the least anadromous species in the Pacific, since it has reduced the freshwater stage to the spawning migration and incubation of the eggs. Some individuals even spawn in the intertidal zone with no real freshwater phase. However, others are entirely freshwater, with completely landlocked local populations.

Behavior

Some species of Salmoniformes are fiercely territorial; others form schools shortly after hatching before they initiate their seaward migration. the most remarkable behavioral characteristic in these fishes is their strong swimming ability (some can leap over obstacles such as waterfalls as high as 10 ft/3 m) and their migratory capability. Almost all, if not all, Salmoniformes can return to the stream of their birth after migrating thousands of miles (or kilometers) in the ocean for one or more years, a behavior known as homing. They use their sense of smell to orient themselves, but some experiments suggest that vision and magnetic clues may also play a role in this behavior. This is not surprising, since other migratory species of animals, such as some birds, can use more than one source of information to achieve their migratory paths. Because of their migrations between fresh and salt waters, salmoniforms have developed a number of physiological adaptations to cope with changes in salinity. This is achieved via osmotic regulation by excreting excess salts through cells in the gills and by having well-developed kidneys, which, in fresh waters, excrete the excess water that diffuses into their blood via the gills.

Feeding ecology and diet

There is variation in feeding habits in this order. Some species feed upon plankton and benthic invertebrates, while others are top predators of other fish species.

Reproductive biology

All salmoniforms lay eggs that are externally fertilized. The egg size is related to the amount of nutrients in the water, with the largest eggs (0.16–0.31 in/4–8 mm), found in nutrient-poor waters. This allows individuals born under those conditions to have enough nutrients to survive, and is followed by direct development. This means that the young look very much like small adults. The size of the egg is also conversely proportional to the number of the eggs. In the case of smaller eggs, the young are less developed after hatching.

Conservation status

The IUCN Red List includes 36 salmoniform species. Of these, four are categorized as Extinct (Coregonus alpenae, C. johannae, C. nigripinnis, and Salvelinus agassizi); four are Critically Endangered; five are Endangered; 10 are Vulnerable; and 13 are Data Deficient.

Because all salmoniforms depend upon migrations into clear, highly oxygenated waters, they are very sensitive to water pollution as well as interruptions in the watercourse by means of dams. This problem is particularly acute for the Pacific salmon, whose numbers and genetic diversity have both declined dramatically.

Significance to humans

Many species of trouts, salmons, chars, whitefishes, and graylings are among the best-known and most intensively studied species of fishes. They have tremendous economic importance in many areas because of their value in both sport and commercial fisheries. This is the reason they have been introduced all over the world. Information about the life cycle and reproduction, some of it based on DNA analysis, has been used to settle disputes between nations regarding the origin of fishes caught in the open ocean, as well as for their management.

Species accounts

Resources

Berra, T. M. Freshwater Fish Distribution. San Diego: Academic Press, 2001.

Elliott, J. M. Quantitative Ecology and the Brown Trout. Oxford: Oxford University Press, 1994.

Johnson, G. D., and C. Patterson. "Relationships of Lower Teleostean Fishes." In Interrelationships of Fishes, edited by M. L. J. Stiassny, L. R. Parenti, and G. D. Johnson. San Diego: Academic Press, 1996.

Lee, D. S., C. R. Gilbert, C. H. Hocutt, R. E. Jenkins, D. E. McAllister, and J. R. Stauffer, Jr. Atlas of North American Freshwater Fishes. Raleigh, NC: North Carolina State Museum of Natural History, 1980.

Lichatowich, J. Salmon Without Rivers: A History of the Pacific Salmon Crisis. Washington, DC: Island Press, 1999.

Page, L. M., and B. M. Burr. A Field Guide to Freshwater Fishes of North America North of Mexico. Boston: Houghton Mifflin Company, 1991.

Taylor, J. E. Making Salmon: An Environmental History of the Northwest Fisheries Crisis. Seattle: University of Washington Press, 1999.

Alekseyev, S. S., V. P. Samusenok, A. N. Matveev, and M. Y. Pichugin. "Diversification, Sympatric Speciation, and Trophic Polymorphism of Arctic Charr, Salvelinus alpinus Complex, in Transbaikalia." Environmental Biology of Fishes 64 (2002):97–114.

Garant, D., P. M. Fontaine, S. P. Good, J. J. Dodson, and L. Bernatchez. "The Influence of Male Parental Identity on Growth and Survival of Offspring in Atlantic Salmon (Salmo salar)." Evolutionary Ecology Research 4 (2002): 537–549.

Klemetsen A., J. M. Elliott, R. Knudsen, and P. Sorensen. "Evidence for Genetic Differences in the Offspring of Two Sympatric Morphs of Arctic Charr." Journal of Fish Biology 60 (2002): 933–950.

Levin, P. S., and M. H. Schiewe. "Preserving Salmon Biodiversity." American Scientist 89 (2002): 220–227.

Proulx, R., and P. Magnan. "Physiological Performance of Two Forms of Lacustrine Brook Charr, Salvelinus fontinalis, in the Open-Water Habitat." Environmental Biology of Fishes 64 (2002): 127–136.

Quinn, T. P., L. Wetzel, S. Bishop, K. Overberg, and D. E. Rogers. "Influence of Breeding Habitat on Bear Predation and Age at Maturity and Sexual Dimorphism of Sockeye Salmon Populations." Canadian Journal of Zoology 79 (2001): 1,782–1,793.

Winfield, I. J., C. W. Bean, and D. P. Hewitt. "The Relationship Between Spatial Distribution and Diet of Arctic Charr, Salvelinus alpinus, in Loch Ness, UK." Environmental Biology of Fishes 64 (2002): 63–73.

Salmon and Trout Association (UK). Fishmongers' Hall, London Bridge, London, EC4R 9EL UK. Phone: (020) 7283 5838. Fax: (020) 7626 5137. E-mail: salmon.trout@virgin.net Web site:

United States Trout Farmers Association. 111 West Washington St., Suite One, Charles Town, WV 25414-1529 USA. Phone: (304) 728 2189. Fax: (304) 728 2196. E-mail: ustfa@intrepid.net Web site: http://www.ustfa.org

The Northwest Salmon Crisis: A Documentary History [cited January 29, 2003].

"Pictures available for Oncorhynchus masou" [cited February 7, 2003].

"Oncorhynchus masou masou" [cited February 7, 2003].

An order of soft-rayed fishes comprising salmon and their allies. They make up the stem group from which most higher teleostean fishes have evolved.

Salmoniformes are generalized fishes characterized by soft or articulated fin rays; adipose dorsal fin usually present; cycloid (smooth) scales; pelvic fin in an abdominal position (well back on the trunk), usually with more than six rays, and with pelvic girdle free from pectoral girdle; pectoral fin placed low on the side and more or less horizontal; upper jaw usually bordered by premaxillae and maxillae; premaxillae not protractile; no weberian apparatus connecting the swim bladder with the inner ear, but a duct joining the bladder with the gut; and branchiostegal rays variable in number and arrangement.

Salmoniform fishes have an imperfect fossil record; they were present in the Cretaceous and likely earlier. The order consists of 8 suborders, 37 families, some 212 genera, and about 950 species. Most are marine fishes, and they are common in all seas. A few are adapted to pelagic or shore waters, most live in the bathypelagic zone, some tolerate arctic seas, and many inhabit warm or cold fresh water, or are anadromous; that is, they enter fresh water to reproduce.

The suborder Salmonoidei includes many of the most important and best known of all fishes, especially in the family Salmonidae, or salmon, trouts, whitefishes, and graylings. The Argentinoidei (argentines, deep-sea smelts, and related fishes), Alepocephaloidei (slickheads), and Bathylaconoidei are found chiefly in deep marine waters. The Galaxioidei are mostly small, fresh-water fishes of south temperate lands, especially Australia and New Zealand. Esocoidei are a small group, the pikes and mudminnows of northern fresh waters. The Stomiatoidei, lightfishes and allies, inhabit the middle depths of the oceans. They are of small size and often grotesque form, and are equipped with photophores. The Myctophoidei is the largest of the suborders. All species are marine; some, including lizardfishes, inhabit shore waters, but the majority are oceanic. Those that live at moderate to considerable depths, such as the lantern fishes, commonly have photophores on the head and body.