Trout farming was introduced to the UK in the 1950s by a DanIsh entrepreneur. Since that time the industry has grown to its current size of almost 360 trout farms.
Rainbow trout (onchorynchus mykiss), although native to North West America has been introduced to regions throughout the world. It is the most popular trout to farm In the UK, as it copes best with the climate and farming system. Other fanned varieties include Brown Trout (salmo trutta) which is indigenous to Britain and other European Countries, also Golden Trout (ancorhynchis mykiss aguabonita) and Blue Trout, albeit in smaller quantities.
Around 16,000 tonnes of Rainbow trout are produced in Britain each year, with around 75% of this farmed by table producers. Most of this number produced is farmed in freshwater in tanks, ponds, netting cages and raceways, with a small quantity farmed In sea cages.
Fish farms usually concentrate on different aspects of the life cycle. Hatcheries produce ova from brood stock and sell on to fingerling producers who grow fingerlings and fry from the eggs. Fingerling producers supply Re-stockers and Table producers. Table producers in turn provide fish to Processors, while Re-stockers will supply Fisheries. Some farms may undertake several of these business activities and in addition may have a shop, a smokery / processing unit, or a Fishery (where anglers can fish in artificially stocked lakes) that is often open to the public.
Trout is farmed widely in the UK, but particularly in central and southern Scotland, south England and North Yorkshire. The main facility needed is a clean river for adequate water supply, in an accessible spot. Trout are cold blooded and are greatly affected by water temperature. The warmer the water, the fewer the fish that can be stocked there and the greater the water flow needs to be; this is because the solubility of oxygen in water decreases with temperature. Ideally, oxygen level. should be 7mg/l or greater. The flow of the water source will in part determine your stocking level. While artificial aeration can be used to increase oxygen levels a sufficient water flow is still needed to remove waste produced by the fish. The total volume of water available on any one site will be a limiting factor in the expansion of a trout farming business.
A farm on a river will consist of ponds, tanks or raceways with the water supplied by gravity. Often a location with a weir is utilised. Cage farming is an altemative method involving the siting of net cages In deep freshwater lakes. The Scottish lochs provide the best location for this method of farming in Britain.
Screens are installed at the inlet channel, to keep out debris and migratory fish. Water should be treated before being discharged back into the river and further screens installed at the outlet. All effluent control is strictly monitored with regular testing by the appropriate Environment Agency.
Although trout can be bred to different sizes, they generally reach their harvesting size at 300-400g in approximately seven and a half months, building muscle by swimming against the current of the water as it passes through the farm.
Once harvested, the trout will be processed for use. Larger farms often have processing facilities on site, which contain machinery designed to gut, fillet, smoke and pack the fish, depending on what is required. The trout may then be sold direct to customers at farm shops, or sent to wholesale markets, caterers or retailers.