Radiant Rainbow Trout (Oncorhynchus mykiss): North America's Valiant, Versatile, Vivid Freshwater Fish

A rainbow arises from an interaction between the rays of the sun and the drops of moisture in the Earth’s atmosphere. It calls to mind bright colors whose sequence from the upper to the lower sides of the arc is as follows: Red, orange, yellow, green, blue, indigo and violet. Within that sequence, red stands out as the brightest, cheeriest and topmost of rainbow colors.

Indeed, it is the similar occurrence of a bright, cheery, foremost slash of red that is behind the name of the rainbow trout.

The common name of the rainbow trout: The rainbow trout is the common name which people most often use to refer to the rainbow trout. Depending upon the locale, it may be joined or replaced by other common names. For example, residents of the Canadian province of British Columbia may refer to their version of the rainbow trout as the Kamloops trout. This designation relates to the trout’s presence in the area around the south central city of Kamloops.

Likewise, residents in the area of North America’s Great Lakes and Pacific Northwest generally call the rainbow trout the steelhead. The term references the rainbow trout which hatches in freshwater, migrates to brackish and sea waters, and returns for freshwater spawning. The word specifically refers to the steel blue color which the rainbow trout sports as a predominantly salt water resident.

A list of alternative common names includes the following:

· Bow;

· Coast rainbow trout;

· Kamloops (Shuswap: Tk'əmlúps, “meeting of the waters”);

· Rainbow;

· Redband, redband trout;

· Silver trout;

· Steelhead, steelhead trout.

The scientific name of the rainbow trout: Johann Julius Walbaum (June 30, 1724-August 21, 1799) is the German gentleman who conferred a scientific name upon the rainbow trout. The Wolfenbüttel-born scientist mastered the disciplines of medicine, natural history and taxonomy. In terms of medicine, he pioneered the use of surgical gloves to discourage post-operative infections. In terms of natural history and taxonomy, he traveled widely and sought the lesser known examples of the animal and plant kingdoms.

One of the places which the German scientist visited was the Kamchatka Peninsula (Russian: полуо́стров Камча́тка, poluostrov Kamchatka) in what is now the Far Eastern Federal Region (Дальневосто́чный федера́льный о́круг, Dalnevostochny federalny okrug) within the Russian Federation (Российская Федерация, Rossiyskaya Federatsiya). It was during his visit that the German naturalist espied specimens of the rainbow trout. The German taxonomist wrote a description and gave the Far Eastern fish the scientific name Salmo (Latin: “salmon”) + mykiss (Kamchatka: mikizha, mykizha, mykz, “trout”) in 1792.

The name experienced subsequent modification. The final change reflected recognition of the following details:

The fish identified as Salmo mykiss by Herr Walbaum in 1792 was similar to the fish identified as Salmo gairdneri by Scottish explorer, naturalist and naval surgeon Sir John Richardson (November 5, 1787-June 5, 1865) in 1836;

The genus most accurately was that of the trout instead of the salmon;

The specific epithet was to respect the older of the two choices in terms of date of first official description and scientific designation.

The name of the species therefore remained the same, mykiss. But the genus was changed to Oncorhynchus (Greek: ὄγκος, onkos, “hook” + ρύγχος, rynchos, “nose”) in honor of the rainbow trout’s close genetic relationship to Pacific salmon.

The home of the rainbow trout: The rainbow trout is native to Asia as well as to North America. In terms of Asia, it is a freshwater native of the Kamchatka Peninsula. From this easternmost extension of mainland Russia, the range runs south to the Amur River (река Аму́р) mouth at the Tartar Strait (Татарский пролив) crossing over to Sakhalin Island (Сахалин) in the east and to the Seas of Okhotsk (Охо́тское мо́ре, Okhotskoye More) in the north and of Japan (Японское море, Yaponskoye more) in the south.

In terms of North America, the rainbow trout is native to freshwater bodies draining into the Pacific Ocean. In terms of Canada, its native range therefore runs through part of the upper Mackenzie River drainage of the Northwest Territories. In terms of Mexico and the United States of America, it spans the continent from Alaska south all the way into northern Mexico.

From its native range, the rainbow trout is widely introduced into all of the world’s continents except Antarctica. For example, it is naturalized in many streams which drain the Blue Ridge and Valley and Ridge provinces of western and northwestern Virginia. Specifically, its introduction into Virginia traces back to shipments from California to the Wytheville hatchery between 1880 and 1882.

Within its native and introduced ranges, the rainbow trout can handle watery habitats in which the following conditions prevail:

· Brackish waters of estuaries and sea waters as long as a return is possible to home streams for spawning;

· Calm pools or pockets within swift waters;

· Clean, fast-flowing, gravel-bottomed streams with pools, riffles, submerged objects and plants, and undercut banks;

· Cool, deep, sandy-bottomed lakes;

· Depths up to 35 feet (10.67 meters);

· Escape cover, especially if the preferred overhanging canopy cover is absent or sparse;

· Water temperatures ranging between 53.6 and 66.2 °F (12 and 19 °C), with 59 °F (15 °C) considered most favorable and with drops below 41 °F (5 °C) and rises above 77 °F (25 °C) constituting hardships.

The appearance of the rainbow trout: The rainbow trout may be characterized as having the following physical traits:

Head:

Jaw angles ending beyond eyes;

Mouth moderate to large;

Body:

Back brassy olive to blue, brown, or yellow green with green and purple iridescent spots;

Belly off to dirty or silvery white;

Lateral line running from the gill covers to the base of the tail;

Mature body length of about 6 to 16 inches (15.24 to 40.64 centimeters) in Virginia and of 20 to 30 inches (50.8 to 76.2 centimeters) in the Great Lakes, with a known maximum of 4 feet (1.2 meters);

Mature body weight of 3 to 8 up to 17 pounds (1.36 to 3.63 to 7.71 kilograms), with a known maximum of 57 pounds (25.85 kilograms);

Sides dark olive to black-spotted, with blotches or stripes of pink, purple or red (or silver in the case of lake dwellers) above;

Fins, rays, spines:

Adipose (Latin: adeps, “soft fat of animals”) fin small and pale olive to amber or purple gray with black spots;

Anal fin with 12 to 16 rays;

Caudal (Latin: caudālis, “of or relating to the tail of an animal”) fin broad, forked and pale olive to amber or purple gray with black spots;

Dorsal (Latin: dorsālis, “of or relating to the back”) fin centrally located along top, with 13 to 17 rays colored pale olive to amber or purple gray with black spots;

Lower fins pale or orange red, purple gray or red, sometimes with black spots;

Pectoral (Latin: pectorālis, “of or relating to the breast”) fin with 11 to 17 rays;

The diet of the rainbow trout: The rainbow trout fry, which hatches attached to its yolk sac, can eat waterfleas within 16 to 21 days of hatching. The young and juvenile rainbow trout expand their diets to include aquatic insects such as caddisflies, mayflies, and midges as well as crustaceans such as crayfish, and the eggs of cutthroat (Oncorhynchus clarkia) and rainbow trout and salmon (Salmo spp). The adult rainbow trout opportunistically preys on algae; crayfish; fish eggs; freshwater shrimp (scuds); insect larvae and adults such as ants, flies and grasshoppers; leeches; other fishes; sideswimmers; snails; and worms.

The predator of the rainbow trout: Birds, fish and mammals are the main predators of the young rainbow trout. Examples of predatory birds include the bald eagle (Haliaaetus leucocephalus), belted kingfisher (Megaceryle alcyon), great blue heron (Ardea herodias), and osprey (Pandion haliaetus). Predatory fish may include the sculpin and smallmouth bass (Micropterus dolomieu). Mammals such as the otter and raccoon (Procyon lotor) also may prey on the young rainbow trout.

Anglers and fishers tend to be the only predators of the adult rainbow trout.

But the rainbow trout also can be preyed upon by bacteria and parasites. In fact, it is susceptible to infections, such as the bacteria-induced enteric redmouth disease and the parasite-induced whirling disease which deforms the skeleton and spines of rainbow trout young. Specifically, enteric redmouth disease is a bacterial infection which is caused by the pathogen Yersinia ruckeri. It reddens eyes, fins, gill tips, mouths and throats because of subcutaneous hemorrhaging. Its incidence will bloat the fish’s abdomen with yellow fluid and erode the fish’s jaw and palate. It will have no effect on human predators of the rainbow trout.

· Control of the disease requires the following care:

· Control of bacteria content through monitoring of freshwater quality;

· Lower density of fish populations in stocked lakes, ponds and reservoirs.

The spawning time of the rainbow trout: The rainbow trout breeds when water temperatures range between 50 and 59 °F (10 and 15°C) during a time of increasing day length and quickening water flow. In the wild, spawning therefore can occur in late winter and spring. In Montana, the rainbow trout may spawn between April and July. In Virginia, it spawns in the wild between February and early May, with peak breeding in March and April.

The rainbow trout migrate to spawning grounds except in small streams, from which they tend not to move. The male gets to the grounds first. But it is the female that prepares a redd, which is a shallow depression in gravel- or sandy-bottomed streams.

The female rainbow trout can produce 200 to 9,000 eggs. She covers the fertilized eggs with gravel or sand. Like the male before her, she then leaves the area.

The ¼ inch (6.35 millimeter), translucent yellow rainbow trout eggs hatch in the wild, generally during the summer and always without any prior or subsequent parental care. They may hatch within 44 to 50 days at water temperatures of 45.5 to 50 °F (7.5 to 10 °C). They may take as long as 101 days to hatch at water temperatures of 37.76 °F (3.2 °C).

The rainbow trout may be sexually mature within 1 year of hatching in Virginia or within 3 to 5 years in Canada. It typically may live another 2 to 3 years. Seven years usually will be considered old age even though the known maximum is 11 years.

The use of the rainbow trout: Fishing, food and medicine are the most visible uses of the rainbow trout.

In terms of fishing, the rainbow trout earns the respect of anglers and fishers. It is a difficult but not impossible fish to catch. In its elusive and evasive maneuvers, it may engage in quite a spectacular sound and light display of darting speeds, leaping heights, and noisy splashes. But the following guidelines may prove useful to keep in mind:

Times:

Dawn or dusk;

Slightly cloudy or overcast weather;

Places:

Deeper waters, mid-summer;

Piers and shores, spring through fall;

Methods:

Careful approach;

Delicate casting or trolling of crank baits, spinners, spoons;

Natural bait, such as cheese, corn, insects, minnows, night crawlers, trout worms.

In terms of food, the rainbow trout is considered a healthy source of 130 calories -- with protein (0.78 ounces, or 22 grams), fat (0.14 ounce, or 4 grams) and saturated fat (0.04 ounces, or 1 gram) -- for every 3 ounce (0.11 kilogram) cooked serving. At its freshest and healthiest best, it may be described as having firm but tender flesh which is light pink to white in color. Additionally, it will be recognized for the shininess of the skin, the moist redness of the gills, and the bulging clearness of the eyes.

But the rainbow trout also may be criticized for its mild, nutty flavor sometimes taking on an earthy quality. Thorough washing may remove the earthy taste. But it should not remove the scales whose jelly allows rainbow trout to be breaded or coated without additional liquid. Neither should it remove the head or tails, whose removal must await the end of baking, broiling, etc., in order to avoid breaking the skin or introducing other flavors into sensitive trout flesh.

In terms of medicine, rainbow trout sperm contains protamine, which counters the anticoagulant heparin.

The future of the rainbow trout: The rainbow trout has the respect of anglers, fishers, and fish-eaters worldwide. It offers both adventurous fishing and healthy gustatory experiences to its admirers. It will continue to do so as long as the damming, logging and sedimentation of its freshwater habitats and the shipping in its brackish and marine environments do not pollute, stain or warm the waters beyond the valiant, versatile, vivid rainbow trout’s ability to survive and thrive.

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the Internet; as well as to Stessily for original artwork included below.

My special thanks to National Oceanic and Atmospheric Administration (NOAA), U.S. Fish and Wildlife Service, U.S. Geological Survey, and U.S. Department of Agriculture for the professionalism which is evinced in the high-caliber data and images which they make available in print and on the internet.

My special thanks also to Virginia Polytechnic Institute and State University, Texas State University-San Marcos, and Pennsylvania Fish and Boat Commission for the high caliber of their online resources.

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Gooch, Bob. Virginia Fishing Guide. Revised Edition. Charlottesville: University Press of Virginia, 1992.

Hart, David. Flyfisher’s Guide to Virginia Including West Virginia’s Best Fly Fishing Waters. Belgrade, MT: Wilderness Adventures Press, Inc., 2006.

Hassan-Williams, Carla, and Timothy H. Bonner. "Oncorhynchus mykiss rainbow trout." Texas State University-San Marcos Department of Biology: Texas Freshwater Fishes. http://www.bio.txstate.edu/~tbonner/txfishes/oncorhynchus%20mykiss.htm (Last accessed November 20, 2011)

Jenkins, Robert E. and Noel M. Burkhead. Freshwater Fishes of Virginia. Bethesda, MD: American Fisheries Society, 1994.

Ladewig, Katheleen F. and Michelle Morat. “Rainbow trout.” Southern Regional Aquaculture Center (SRAC) Publication No. 224, January 1995. http://aqua.ucdavis.edu/DatabaseRoot/pdf/224FS.PDF (Last accessed November 20, 2011)

"Rainbow Trout, Oncorhynchus mykiss." EFISH: The Virtual Aquarium of The Department of Fisheries & Wildlife Sciences of Virginia Tech. http://cnre.vt.edu/efish/families/muskell.html (Last accessed November 20, 2011)

"Rainbow Trout Oncorhynchus mykiss." Pennsylvania Fish & Boat Commission (PFBC) Gallery of Pennsylvania Fishes Chapter 15: Trout & Salmon, Family Salmonidae. http://www.fish.state.pa.us/pafish/fishhtms/chap15trout.htm (Last accessed November 20, 2011)

Rohde, Fred C., Rudolf G. Arndt, David G. Lindquist, and James F. Parnell. Freshwater Fishes of the Carolinas, Virginia, Maryland, and Delaware. Chapel Hill and London: The University of North Carolina Press, 1994.

Copyright Sunday, November 20, 2011 by Derdriu