River trout
Salmo trutta fario, sometimes called the river trout, is a river-dwelling freshwater predatory fish from the genus Salmo of the family Salmonidae. It is one of the three main subspecies or morphs of the brown trout (Salmo trutta), besides sea trout (Salmo trutta trutta) and the lacustrine trout (Salmo trutta lacustris).
Depending on the supply of food, river trout measure 20 to 80 cm (0.7–2.6 ft) in length; exceptionally they may be up to 1 m (3.3 ft) long and weigh up to over 13 kg (29 lb), although they usually attain an average weight of up to 2 kg (4.4 lb). Their back is olive-dark brown and silvery blue, red spots with light edges occur towards the belly, the belly itself is whitish yellow. They can live for up to 18 years.
Like other salmonids, river trout live in cool, fast-flowing, oxygen-rich, clear waters with gravel or sandy riverbeds. Their native ranges occur across almost all of Europe, from Portugal on the Iberian Peninsula to the Volga in Russia, and are found as far north as Lapland. They can be found in most of the tributaries of the northern Mediterranean and western Black Sea, but do not occur in Greece, Central Anatolia and the Caucasus regions or on the islands of Corsica, Sardinia and Sicily.
River trout are very faithful to their habitat, only leaving the home range stream for smaller upstream headwaters to reproduce. Even after being disturbed they will return to their traditional sites. The adult river trout requires its own territory. During the day it is hidden in the shadows of the river bank, facing upstream.
Depending on size and habitat, they feed mainly on insects and larvae, small baitfish (such as European bullhead), small crustaceans, snails and other water animals. Cannibalism has also been frequently observed among river trout. They are fast-swimming pursuit predators, but in faster-flowing rivers and streams they are usually opportunistic and will take prey that is floating past by the current.
The river trout has special significance as a host fish for the glochidia of the freshwater pearl mussel (Margaritifera margaritifera).
River trout spawn between October and January in the northern hemisphere, and introduced populations in the southern hemisphere spawn between May and June. The fish uses rapid fanning of the tail and caudal fin on a rock riverbed to make several shallow pits, into which about 1,000 to 1,500 reddish eggs 4–5 mm (0.16–0.20 in) in size are laid. The fish larvae emerge after two to four months.
