Principles of Genetics and Breeding

14.1.7.Rainbow trout and other salmonids

Techniques of artificial reproduction were developed in the 18^th and 19^th centuries, leading to the production of brown (Salmo trutta) and rainbow trout (Salmo gairdneri) in captivity.

Originally, “the fish produced were mainly used for restocking angling waters and commercial net fisheries.”

In the latter half of the 19^th century, brown trout in Europe and rainbow trout in North America were genuinely ‘farmed’, in the sense that although originally from wild stocks, brood fish were kept and the fish spent their whole life cycle in an artificial environment.

At present close to 200 stocks of different trout species; rainbow trout, brown trout, brook trout (Salvelinus fontinalis), lake trout (Salvelinus namaycush), and cutthroat trout (Salmo clarki) are maintained at state fish and game departments in the U.S. Further strains are maintained outside of the U.S.

Among salmonids, rainbow trout is the major species under cultivation and the most highly domesticated.

A large number of rainbow trout strains (54) are maintained in the U.S. including a high proportion of domesticated ones. Rainbow trout are endemic to Western North America from where they were distributed throughout North America and other countries. The major source of these transfer appears to be from the McCloud River in Northern California.

Thus, in spite of their natural distribution from Alaska to Mexico, presumably resulting in a corresponding genetic variation, the origin of many domestic strains is much more restricted.

Another salmonid of commercial importance in aquaculture is the Atlantic salmon (Salmo salar). Its culture in sea cages was initiated in Norway in the 1960s and is now also practiced in other areas, such as off the northeast coast of Britain.

Natural salmon populations were sampled from different Norwegian rivers. These fish were spawned in hatcheries and their progenies grown to maturity first in tanks during the freshwater stage and then in sea cages.