Rainbow Trout

Names in dialect: iridea.

Rainbow trout originate from the rivers of North America that flow out into the Pacific Ocean, from Alaska to California, where there are both migratory and freshwater populations, which are very different. They have a greenish-brown colour body, covered with a large number of round black markings, which also appear on the dorsal and caudal fins; a red or pink band runs along the flanks, which becomes more vivid during the spawning period in the male, which also has a hook-shaped lower jaw. They can exceed lengths of 70 cm and 7 kg in weight. In Trentino, in the few streams where they have acclimatised, they rarely exceed 30 cm.
They live in running and lake waters that are cool in temperature (lower than 20 - 22 °C) and well oxygenated. Stocks that have been farmed for many generations in fish farms are less discerning in terms of quality of the environment, and easily survive in habitats that would not be suitable to original stock.
They are basically carnivorous, eating aquatic invertebrates and small fish. A diet based on crustaceans gives the meat a “salmon” colour, which can be achieved in fish farming by using a specific foodstuff.
The spawning period is usually between October and March, but some stocks acclimatised in mountain springs breed in May. Spawning is basically the same as for native trout. Sexual maturity is reached between the 2^nd and 3^rd year. Each female produces from 1000 to over 3000 eggs per kg of body weight. The eggs are 3.5 - 5 mm in diameter and require a total of 350 degrees centigrade to hatch.
Rainbow trout were imported into Trentino for the first time in 1885 by the Torbole hatchery, and breeding started immediately. Rainbow trout farming is a thriving business and an important source of income. There are about sixty fish farms in the province of Trento that raise rainbow trout. Large numbers of fish have been introduced since the beginning of last century; however the presence of rainbow trout in public waters today is fairly limited. The species has hardly ever managed to acclimatise, and its introduction is increasingly being banned because it can cause imbalances, such as the disappearance of Arctic char from high latitude lakes. Rainbow trout, especially those that have grown in a natural environment, are an excellent food fish.