The main species farmed in Switzerland today are trout, whitefish and northern pike. Two kinds of farming can be distinguished: intensive commercial fish farming and breeding for restocking purposes.
One species that has proven particularly amenable to intensive farming is the rainbow trout, which was introduced into Europe from the United States in around 1880. Under certain conditions, it can be grown from the hatching stage to what is known in the trade as the “portion size” (that is, the size at which it can be served in a restaurant) in one year, a rate of growth which is not possible in nature, due to lower water temperatures and fewer available food sources.
Intensive farming is carried on almost exclusively in privately-owned facilities, while the task of breeding for restocking purposes in Switzerland is largely entrusted to the cantons, which often delegate it in turn to fishing companies.
The spawning process is an extremely delicate operation. By applying slight pressure in the direction of the opening adjacent to the anal opening, the eggs are removed from the females and the sperm from the males. These are then delicately mixed using a goose feather: this is how the eggs are artificially fertilised.
Incubation takes place in special containers; the eggs must remain immersed in cool, oxygenated water. The incubation period varies from species to species and according to the temperature of the water. Immediately after the eggs hatch, the tiny fish are extremely vulnerable, as they are still feeding on the reserves which they have in the yolk sac: only after they have exhausted these reserves are they capable of taking sustenance from the environment.
It is not difficult to imagine the many dangers to which the fry would be exposed in nature. The mere fact that the water is not completely clean, in some sensitive species, can prevent the eggs from hatching. This is why, increasingly, fish are farmed through to the pre-fingerling or fingerling stage or even fish aged up to a year before they are released into open waters.
Fish adapt quickly to their new environmental conditions, making it possible to keep many rivers abundant in fish: rivers which, without such artificial restocking, would have long been depleted of fish stocks.