The Rainbow Trout
Richard D. Moccia & David J. Bevan
OAC Publication 1991, July 1991
AGDEX 485 06

Did you know that the rainbow trout with its scientific name, Oncorhynchus mykiss, is a species not native to most regions of Canada, or indeed, the world? In fact, the original range of the rainbow was limited to the eastern Pacific Ocean and the freshwater drainage basins mainly west of the Rocky mountains. The historical distribution extended from Mexico to Alaska, but was not known to occur in other regions of the continent, or for that matter, most other countries in the world. As we are now aware, this incredibly versatile (or plastic) species, is thriving well - both as a wild and farmed species - in many countries around the world. The rainbow trout has been introduced to Africa, Japan, Southeast Asia, most of South America and Central America, Australia and New Zealand, and also widely throughout Europe and Hawaii. In Canada the species now exists in every province (and the Territories) and is known to occur naturally in the far northern Alsek River in the Yukon.

There is some confusion about the early transfers of rainbow trout from the west coast, Pacific Ocean watershed. It is generally accepted that the first movement of rainbow trout occurred to New York State in 1874 from a native spring spawning stock from Campbells Creek on the McLeod River, California. The pioneering fish culturist Seth Green is attributed with initiating these first transfers. It is believed that many of the cultured rainbow trout stocks today, were developed from this original strain of McLeod River fish. In 1879, the United States Fish Commission established a spawning station for the taking and distribution of trout eggs around the United States. This facility was closed nine years later in 1888, after a whopping total of 2.7 million eggs had been collected and distributed! The Great Lakes Basin first received fish in 1876 into the Au Sable River, Lake Huron, State of Michigan. The Great Lakes received a number of other plantings including: L. Ontario - 1878; L. Michigan - 1880; L. Erie - 1882; and L. Superior -1883.

The original introductions into Canada are suspected to have occurred in 1877 to Newfoundland, and 1899 to New Brunswick and Nova Scotia. The Province of Ontario was rainbowless until about 1904, although some authors have traced suspected transfers back to 1883. The Ontario government introduced rainbow trout in 1914, and transferred fish in 1917 to the governments' Normandale Hatchery on Lake Erie to establish a brood stock program. Saskatchewan received fish in 1924, Prince Edward Island in 1925, Manitoba in 1938, the Yukon in 1943 and finally Alberta in 1958.

Of all the scientific and common names that have been given to the rainbow trout, it is now accepted that the scientific name, Oncorhynchus mykiss should replace the long used Salmo gairdneri which the fish was known by for some 150 years. There is also confusion about the difference in a so-called 'normal' rainbow, versus a 'steelhead' rainbow or a 'Kamloops' trout. These are all identical species, (ie. the same Oncorhynchus mykiss). However, there are differences in the life history of the individual groups. Specifically, the steelhead trout generally refers to the large, west coast sea-run fish which utilize both freshwater and saltwater as part of their native habitat. Kamloops trout refers to a silvery-coloured, freshwater lake form originally described in 1892. Smaller, and usually more darkly pigmented fish inhabiting streams and rivers are normally referred to simply as rainbow trout. Some authors have suggested that it was the steelhead, seawater strain that was originally introduced into the Great Lakes, and these fish still utilize the Great Lakes and the surrounding tributary streams in much the same way that sea-run trout move between saltwater and freshwater rivers for spawning. Fishermen often call any big rainbow trout a steelhead, but it is more likely that these are just simply large fish which may have originated from any number of sources. Great Lakes trout are a complex mixture of wild and domestic strains from various geographical origins that are now widespread and self-sustaining, or naturalized.

It is also interesting to note that the rainbow trout, and all of the west coast stocks that provided the rest of the world with seed fish, were, and still are, true genetic spring-spawners. In fact, some California populations are reported to spawn twice a year. Most of the European and Canadian farmed stocks have transformed themselves, at least behaviourally, to fall spawning strains, with photoperiod being the prime determinant of spawning time. This is noteworthy, considering the genetic, spring spawning heritage of the fish.

At any rate, the rainbow trout, by all its names, is here to stay, and for at least the next 10 to 15 years will provide the foundation for aquaculture production in this province. It is one of the most popular farmed and sports fish in Ontario. Current data indicate that Ontario farmed some 2,500 metric tonnes of rainbow trout in 1990, which contributes in its own small way to the overall world production of rainbow trout which is estimated at 300,000 metric tonnes.

Anybody who would like additional information on the rainbow trout is encouraged to either call the Aquaculture Extension office or check the following references: W.B. Scott and E.J. Crossman, 'Freshwater Fishes of Canada'; H.R. MacCrimmon, 'World Distribution of rainbow trout (Salmo gairdneri)', Journal of Fish. Res. Board Canada, 1971,28:663-704; and H.R. MacCrimmon and B.L. Gots, 'Rainbow Trout in the Great Lakes", Ontario Ministry of Natural Resources, 1972.
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