Brown Trout - Stocking, Farming and Non-native Brown Trout

Stocking, Farming and Non-native Brown Trout

The species has been widely introduced for sport fishing into North America, South America, Australia, New Zealand and many other countries, including Bhutan, where they are the focus of a specialised fly fishery. First planting in the United States occurred April 11, 1884 into the Baldwin River, one mile east of Baldwin, MI. Brown trout have had serious negative impacts on upland native fish species in some of the countries where they have been introduced, particularly Australia. Because of the trout's importance as a food and game fish, it has been artificially propagated and stocked in many places in its range, and fully natural populations (uncontaminated by allopatric genomes) probably exist only in isolated places, for example in Corsica or in high alpine valleys on the European mainland.

Farming of brown trout has included the production of infertile triploid fish by increasing the water temperature just after fertilisation of eggs, or more reliably by a process known as pressure shocking. Triploids are favoured by anglers because they grow faster and larger than diploid trout. Proponents of stocking triploids argue, because they are infertile, they can be introduced into an environment that contains wild brown trout without the negative effects of cross-breeding. However, stocking triploids may damage wild stocks in other ways. Triploids certainly compete with diploid fish for food, space and other resources. They could also be more aggressive than diploid fish and they may disturb spawning behaviour.

Scottish and Irish sea trout populations in recent years have seriously declined, possibly due to infestation by sea lice from salmon farms.