The brown trout is an economically important species, particularly due to its popularity with anglers, and stocks are maintained in many areas by artificial introductions (2). This fish feeds on invertebrates, insect larvae, aerial insects, and molluscs, as well as the occasional fish and frog (4). Spawning occurs between January and March, when females are accompanied by a number of males. The eggs, which are fertilised externally, are covered with gravel by the female. For the first days after hatching, the young fish (fry) derive their nutrients from their large yolk sacs; they then feed on small arthropods, such as insect larvae (2). The maximum-recorded life span of a brown trout is 5 years (4).
The brown trout is a beautiful fish, similar in general shape to the salmon; the back is dark, the sides pale, and both are flecked with variable reddish spots that have pale borders (3). The belly is a creamy yellowish-white. Juveniles and immature adults can be distinguished as they have bluish-grey spots, and adult males have a strongly curved lower jaw (2).
The brown trout is found throughout Europe; those that live in rivers which empty into the North Sea and the Baltic Sea belong to the subspecies Salmo trutta fario, those that live in rivers that empty into the Black Sea are of the subspecies Salmo trutta labrax, and those in rivers emptying into the Mediterranean belong to the subspecies S. t. macrostigma (2). The brown trout (Salmo trutta fario) is found throughout the British Isles (3).