Salmonids

aka: Trout
aka: Salmon

Salmonids include chars, graylings, salmon, trout, and freshwater whitefishes, all of which belong to the superorder Protacanthopterygii, order Salmoniformes, family Salmonidae, three lineages or subfamilies (Coregoninae, Thymallinae, and Salmoninae), eleven extant genera, and about 120 species. There are thirty-nine species known in North America. The family is widely distributed, with various species found north of the equator in Asia, Europe, and North America. Some important North American genera include Coregonus, Oncorhynchus, Prosopium, Salmo, Salvelinus, and Thymallus. Although no members are native to Arkansas, salmonids have been introduced, primarily for purposes of sports fishing.

The family initially appears in the fossil record in the middle Eocene (48 to 38 million years ago) from fossils found in central British Columbia, Canada. A hiatus appears in the salmonine fossil record until about the late Miocene (seven million years ago). Based on the most current data, salmonids diverged from the rest of teleosts (bony fishes) no later than the late Cretaceous (101 to 66 million years ago). In Arkansas, fossil deposits dating from the Pleistocene epoch (2.6 to 0.01 million years ago) of a char, likely a brook trout (Salvelinus frontalis), were found near Mammoth Spring (Fulton County).

Morphologically, salmonids have abdominal pelvic fins placed far back on the body, a fleshy adipose fin toward the rear of the dorsum, no fin spines, a pelvic axillary process at the upper edge of the pelvic fin base, many small rounded smooth-edged (cycloid) scales embedded in slimy mucus, and forked caudal fins. Their mouth contains a single row of sharp teeth, and there are numerous pyloric caecae in the gut. They also possess a small, triangular projection called the axillary process at the upper end of the base of the pelvic fin. The smallest species is 13.0 cm (5.1 in.) long, but most are much larger, with the largest reaching nearly 2.0 m (6.6 ft.). The Taimen (Hucho taimen) from Siberia is the largest salmonid, with a maximum weight of 80.0 kg (175 lbs.) and lengths of about 1.5 to 1.8 m (4.9 to 5.9 ft.).

Virtually all salmonids are coldwater anadromous fishes that spawn in well-oxygenated freshwater; they spend most of their lives in seas (saltwater) in most cases, returning to streams only to reproduce. They have incredible homing ability, and Pacific salmon (Oncorhynchus spp.) are fine examples of such. They begin their lives in freshwater streams, lakes, and rivers and then migrate to the ocean as small fish called smolts. After they transition from freshwater to saltwater and grow into adults in the high seas of the Northern Pacific Ocean, a biological clock tells them when it is time to return to the place of their hatching to spawn another generation. For the native peoples of the Pacific Rim, salmon are a primary source of protein for their families to eat all winter. The Northern Pacific Ocean provides the primary source of wild salmon that is harvested commercially and eaten by people all over the world. The Alaska salmon fishery is responsible for about ninety percent of wild-caught salmon in North America.

Salmonids are top predatory fishes that feed on small crustaceans, aquatic insects, and smaller fish. They are among the most valuable game and food fishes. For example, the Atlantic salmon (Salmo salar) is a famous sport fish. Coho salmon (Oncorhynchus kisutch) and Chinook salmon (Oncorhynchus tshawytscha) appear to be well established in the upper Great Lakes, and a population of pink salmon (Oncorhynchus gorbuscha) is established in Lake Superior. Unfortunately, however, introduction of salmonids as game and food fishes has been detrimental to native species.

Interestingly, all extant salmonids show evidence of partial tetraploidy (two paired homologous sets of chromosomes), as studies have shown the genome has undergone selection to regain the normal diploid (2n) condition. Research on the rainbow trout (Onchorhynchus mykiss) has revealed that the genome is still partially tetraploid. This pattern is thought to be present in the remainder of extant salmonids.

In Arkansas, there are five species of non-native trout: the brown trout (Salmo trutta), rainbow trout (O. mykiss), cutthroat trout (Oncorhynchus clarkii), brook trout (Salvelinis frontalis), and lake trout (Salvelinis namaycush). They have been, at one time or another, introduced into the state’s waters, mostly in tailwaters below dams to increase recreational fishing. The initial tentative stocking of rainbow trout in Arkansas was made in 1948 in North Fork River below Norfork Dam. During the next two years, additional O. mykiss as well as S. trutta were stocked there. Trout were also introduced into the White River below Bull Shoals Dam in 1952, and two years later, a significant fishery had become established. Rainbow trout were once stocked in Lake Ouachita but are no longer introduced. The majority of trout (primarily rainbow, brown, and cutthroat) stocked in the state come from federal hatcheries, particularly the Norfork National Fish Hatchery administered by the U.S. Fish and Wildlife Service. Their present production is over 226,000 kg (250 tons) annually. Others come from the Jim Hinkle Spring River State Fish Hatchery at Mammoth Spring, which is the Arkansas Game and Fish Commission’s only coldwater hatchery. It is also one of the largest trout hatcheries in the southeastern United States.

Brown Trout
Originally from Europe, the brown trout (often referred to as the brownie) is an exotic fish that is not indigenous anywhere in the United States. It was first stocked on the North American continent (Michigan and New York) in 1883 and is native to Europe and parts of Asia, from Afghanistan and the Aral Sea across Europe to the British Isles and Iceland, and back across Scandinavia to Cape Kanin, Russia, and farther on to the Barents Sea. Today, S. trutta is found throughout the United States in the Great Lakes area, south in the Appalachians to the northern edge of Georgia, and farther south in some high-gradient streams and rivers of the Mississippi River drainage system, throughout much of Nebraska, and in every state west of Texas and Nebraska to the Pacific coast.

This trout is a sleek, streamlined fish with soft-rayed fins and small cycloid scales. The dorsal fin has ten to thirteen dorsal rays and round, black spots, and the body possesses small reddish or orange spots surrounded by a lighter halo. The caudal (tail) fin is usually not forked and usually does not have spots, and the adipose fin is orange to orange-red. The anal fin usually has nine to twelve rays. The all-tackle world-record S. trutta was caught in 2013 in New Zealand and weighed 19.1 kg (4.0 lbs., 1.0 oz.). The conventional tackle world record brown trout was caught in 1992 by Howard Collins below Greers Ferry Lake on the Little Red River and weighed 18.3 kg (40.0 lbs., 4.0 oz.).

Brown trout (S. trutta) is one of the most difficult types of trout to capture by any angling method. It will sometimes be startled by live bait or a fly whereas at other times take no notice of them. Sculpins (Cottus spp.) are also used as bait. In Arkansas, S. trutta inhabits streams in the White River below Bull Shoals Dam and in the Little Red River. It is often found around logs and undercut banks or in deep waters below riffles. It appears to be tolerant of turbid and polluted waters more so than other trout. Young S. trutta feed on aquatic invertebrates, whereas the carnivorous adults feed on fish and crayfish.

This trout spawns in the fall or early winter and has been reported to be successful in breeding in some waters in Arkansas, particularly the White River below Bull Shoals. Its reproduction is similar to other trout, with females digging a gravel pit in a riffle and depositing 4,000 to 12,000 eggs that are fertilized by the male. Neither sex exhibits parental care. Brown trout have the ability to hybridize with brook trout (S. fontinalis), which results in a strikingly marked fish called a “tiger trout.” Some minor releases of tiger trout have been made in some Arkansas waters; however, few of the eggs or hatchlings of this cross survive due to genetic differences between the two genera, and offspring are unable to reproduce. Since populations of S. fontinalis in Arkansas are not self-sustaining, regular stocking in cold streams is necessary to maintain a population for fishing in the state. Their lifespan averages about four years, but some are capable of surviving for eight or more years.

Rainbow Trout
Rainbow trout (O. mykiss), formerly Salmo gairdneri, are native to the west coast of North America in coastal streams from southern Alaska to Durango, Mexico, and far inland to central Alberta, Canada, and Idaho and Nevada. It has been extensively introduced across the lower Canadian provinces and throughout the area of the Great Lakes to the Atlantic coast, south in the Appalachians to northern Georgia and Alabama, east in the southern United States to western Texas, and sporadically in the central United States as well as above the Great Lakes on the Atlantic coast. It has also been removed to Africa, Australia, New Zealand, South America, Japan, southern Asia, Europe, and Hawaii. There are six highly distinctive recognized subspecies. Although there is no direct commercial demand for O. mykiss, it is sometimes taken by Pacific salmon fishermen and is also pond reared in Japan and Europe, where it is sold as frozen whole fish.

This trout has small cycloid scales and a small, fleshy adipose fin on the back behind the dorsal fin, with ten to twelve rays. There is a small triangular (axillary) projection at the base of the pelvic fin, which has nine to ten rays. The upper parts of the rainbow trout are dark olive green and thickly speckled with black spots; the undersides are silvery white. There are prominent dark spots on the caudal fin. The side lacks orange or reddish spots, but there is a pink or reddish longitudinal stripe. The caudal fin is slightly forked, and the anal fin averages ten or eleven rays. The all-tackle world record O. mykiss was caught in Canada in 2009 and weighed 21.8 kg (48.0 lbs.). The Arkansas rod-and-reel record rainbow trout was caught in the White River in 1981 and weighed 8.6 kg (19.0 lbs., 1.0 oz.).

Rainbow trout require Arkansas waters that are constantly below 70°F, so they are limited mostly to Ozark and Ouachita spring branches and spring-fed streams, where cold water releases just upstream are discharged from the lower levels of reservoirs. The Arkansas Game and Fish Commission operates trout hatcheries and has stocked them in the state at various sites, including the White River below Beaver and Bull Shoals dams and North Fork River below Norfork Dam south to Lakes Catherine, Hamilton, and Ouachita; the Ouachita River below Remmel Dam; and the Little Missouri River above and below Lake Greeson. Where trout have established self-sustaining populations, creel and size limits help keep those populations healthy.

Rainbow trout feed on a variety of invertebrates and vertebrates, but aquatic insects, terrestrial insects, snails, and small fishes often make up the bulk of their diet. There is a growing demand for trout fishing in Arkansas, and angling-related activities contribute millions of dollars annually to the state’s economy.

Spawning of O. mykiss in Arkansas has met with limited success, but where it does occur, these fish deposit eggs in clean, swift gravelly riffles from late December to early February. From 2,500 to 4,500 eggs are covered with gravel, and the female leaves them unguarded, although during actual spawning, both sexes defend the nest against other fishes. Rainbow trout can hybridize with other trout, especially with cutthroat (O. clarkii) and golden trout (Oncorhynchus mykiss).

Cutthroat Trout
The cutthroat trout (O. clarkii) is one of the most widely distributed of all the western trouts of North America. The anadromous forms are distributed from the Eel River in California, north to Prince William Sound, Alaska. Inland (non-anadromous) forms occur from southern Alberta, Canada, to as far south as New Mexico, and as far east as Colorado and most of Montana and west to Alberta and eastern California. In Arkansas, it has been stocked into the White River below Bull Shoals Dam and in the North Fork River below Norfork Dam. There are fourteen highly distinctive recognized subspecies.

This trout can be a highly variable fish, both in coloration and size. It has a yellow, orange, or red streak or dash (cutthroat mark) in the skin fold on each side under the lower jaw. The color of the body ranges from cadmium blue and silvery (sea run) to olive green or yellowish green. There may or may not be red on the sides of the head, front part of the body, and belly. The body is covered with black spots that extend onto the dorsal and adipose fins and then onto the caudal fin. On the caudal fin, the spots radiate evenly outward as they do in other trout species. Interestingly, only the cutthroat trout has hyoid teeth (teeth on the back of the tongue). The caudal fin of O. clarkii is slightly forked, and all the fins are soft rayed. The all-tackle world record was an O. clarkii caught in California in 1925 that weighed 18.6 kg (41.0 lbs.). The rod-and-reel record in Arkansas was a specimen caught in the White River in 1985 that weighed 4.5 kg (9.0 lbs., 9.0 oz.).

Cutthroat trout inhabit small, gravel-bottomed mountain streams, rivers, and lakes. It eats mostly aquatic insects, but larger adults will feed on minnows and other fishes. They are early spring spawners in their native range, and reproductive behavior is similar to other trout. This trout has not been found to reproduce naturally in Arkansas. It has been reported to hybridize with rainbow and golden trout, as well as other close relatives.

Brook Trout
The brook trout (S. fontinalis), actually a type of char, is native to northeastern North America, generally from the Great Lakes north to the Hudson Bay and east to the Atlantic and Arctic coasts. These trout (often called brookies) occur in the Appalachians southeast of the Great Lakes to the northeastern corner of Georgia, where they inhabit clear, cold mountain streams and lakes and even small creeks and ponds. They have been introduced into areas of upland elevation throughout most of western North America and can be found in scattered locations from the central portions of the lower Canadian Provinces south nearly to Mexico (west of Texas). They have also been introduced into other continents, notably South America (Argentina) and Europe. The term “coaster” refers to a brook trout that moves into lakes to feed and returns to streams to spawn.

The lower fins (pectoral, pelvic, and anal) of the brook trout have a milky white leading edge, distinguishing chars from trouts. It is often identified by the light green to cream colored vermiculations (wavy lines) on the dorsum and top of the head, and by the pale yellowish or greenish spots and the red spots with blue halos (ocelli) on the sides. The dorsal fin, with its ten to fourteen rays, has heavy black vermiculations. The basic color of the dorsum is olive green to dark brown, lightening to white on the belly. Once spawning nears, the lower flanks and belly of the males turn bright orange-red with a black edge on the lower sides. Sea run specimens turn silvery, often with a light iridescent purplish sheen, and with only the red spots showing. The caudal fin is spotted and only very slightly forked. The all-tackle world record S. fontinalis was caught in 1915 and weighed 6.6 kg (14.0 lbs., 8.0 oz.). The rod-and-reel record in Arkansas was a brook trout caught in the North Fork River in 2002 that weighed 2.3 kg (5.0 lbs.).

In Arkansas, only a few S. fontinalis have been stocked in the North Fork River below Norfork Dam; some have been reported to migrate downstream into the White River. Here, brook trout inhabit cold, clear waters and are often found near cover such as rocks, logs, and undercut banks. Catching brook trout is very rare in the state, but they rate extremely high as a food and game fish. Its flesh is white to bright orange and is considered delicious. It is one of the most popular game fishes in northeastern North America, actively sought by both fly fishing and spinning enthusiasts.

Young brook trout feed on plankton and aquatic insects, whereas the adults eat insects and small fishes. Although it has not been reported to breed successfully in Arkansas, in its native range, S. fontinalis spawns in late fall and winter at water temperatures of 12.8°C (55°F). The female digs a pit for depositing eggs in gravelly riffles, the male moves in to release milt (sperm) over the eggs, and the female then buries them; neither sex takes part in parental care.

Lake Trout
Lake trout (S. namaycush), another char, are found throughout most of Canada and into Alaska as well as the Great Lakes, including sections of the western United States, where they have been introduced. Salvalinus namaycush seeks out the deeper, cooler waters of lakes, some as deep as 30 to 60 m (100 to 200 ft.). In northern lakes, it may occur in either shallow or deep water. In Arkansas, lake trout were first stocked in 1986 in Bull Shoals and Greers Ferry lakes. Some of the same specimens were later found below Greers Ferry Lake in the Little Red River.

Like other chars, it has white leading edges on all the lower fins and light-colored spots on a dark background, versus the dark spots on a light background characteristic of salmon and trout. The body is typically grayish to brownish, with white or nearly white spots that extend onto the dorsal, adipose, and caudal fins. There are no red, black, or haloed spots of any kind. They have a more deeply forked caudal fin than other chars. The all-tackle world record S. namaycush is a 32.7 kg (72.0 lb.) specimen caught in 1995 in Canada. In Arkansas, the rod-and-reel record lake trout is a 5 kg (11.0 lb., 5.0 oz.) specimen caught in 1997 in Greers Ferry Lake.

Many different parasites have been reported from the five species of salmonids introduced in Arkansas, as well as other species. One of the main hosts of piscicolid leeches is the rainbow trout. However, no parasites have been reported from those introduced populations in the state.

For additional information:
Allendorf, F. W., and G. H. Thorgaard. “Tetraploidy and the Evolution of Salmonid Fishes.” In Evolutionary Genetics of Fishes, edited by B. J. Turner. New York, NY: Plenum Press, 1984.

Baker, R. F., and W. P. Mathis. “A Survey of Bull Shoals Lake, Arkansas, for the Possibility of an Existing Two-Story Lake Situation.” Proceedings of the 21st Annual Conference of the Association of Game and Fish Commission 1967: 360–368.

Behnke, Robert J. “Salmo clarki (Cutthroat Trout).” In Atlas of North American Freshwater Fishes, edited by David S. Lee, et al. Raleigh: North Carolina State Museum of Natural History, 1980.

———. “Salmo gairdneri (Rainbow Trout).” In Atlas of North American Freshwater Fishes, edited by David S. Lee, et al. Raleigh: North Carolina State Museum of Natural History, 1980.

———. “Salmo trutta (Brown Trout).” In Atlas of North American Freshwater Fishes, edited by David S. Lee, et al. Raleigh: North Carolina State Museum of Natural History, 1980.

Behnke, Robert J. Trout and Salmon of North America. First Chanticleer Press Edition. New York: The Free Press, 2002.

Berthelot, C., and F. Brunet, et al. “The Rainbow Trout Genome Provides Novel Insights into Evolution after Whole-Genome Duplication in Vertebrates.” Nature Communications 5 (2014): 1–10.

Carlander, K. D. Handbook of Freshwater Fishery Biology, Vol. 1. Ames: Iowa State University Press, 1969.

Cope, Oliver B. “Annotated Bibliography of the Cutthroat Trout.” Fishery Bulletin of the Fish and Wildlife Service 140 (1958): 1–30.

Estes, R. D., ed. Bibliography of the Eastern Brook Trout Salvelinus fontinalis (Mitchell). Cookeville, TN: Trout Commission Division of the American Fisheries Society, 1983.

Hendricks, David L. “Salvelinus fontinalis (Brook Trout).” In Atlas of North American Freshwater Fishes, edited by David S. Lee, et al. Raleigh: North Carolina State Museum of Natural History, 1980.

Hoffman, Glenn L. Parasites of North American Freshwater Fishes. 2nd ed. Berkeley: University of California Press, 2009.

Lee, David S. “Salmo trutta (Brown Trout).” In Atlas of North American Freshwater Fishes, edited by David S. Lee, et al. Raleigh: North Carolina State Museum of Natural History, 1980.

Martin, B., S. P. Platania, and Don E. McAllister. “Salvelinus namaycush (Lake Trout).” In Atlas of North American Freshwater Fishes, edited by David S. Lee, et al. Raleigh: North Carolina State Museum of Natural History, 1980.

Matthews, William J., and R. S. Matthews. “Additions to the Fish Fauna of Piney Creek, Izard County, Arkansas.” Proceedings of the Arkansas Academy of Science 32 (1978): 92.

Page, Larry M., and Brooks M. Burr. Peterson Field Guide to Freshwater Fishes of North America North of Mexico. 2nd ed. Boston: Houghton Mifflin Harcourt, 2011.

Quinn, T. The Behavior and Ecology of Pacific Salmon and Trout. Seattle: University of Washington Press, 2004.

Robison, Henry W., and Thomas M. Buchanan. Fishes of Arkansas. Fayetteville: University of Arkansas Press, 1988.

Stoneking, M., D. J. Wagner, and A. C. Hildebrand. “Genetic Evidence Suggesting Subspecific Differences Between Northern and Southern Populations of Brook Trout (Salvelinus fontinalis).” Copeia (1981): 810–819.

Chris T. McAllister
Eastern Oklahoma State College

Last Updated: 07/17/2019