The Brown Trout is an originally European species of salmonid fish. The Brown Trout is a medium-sized fish, growing to 20 kg or more and a length of about 100 cm in some localities, although in many smaller rivers, a mature weight of 1 kg (2 lb) or less is common.
The fish is not considered to be endangered, although, in some cases, individual stocks are under various degrees of stress mainly through habitat degradation, overharvest and artificial propagation leading to introgression. Increased frequency of excessively warm water temperatures in high summer causes a reduction in dissolved oxygen levels which can cause 'summer kills' of local populations if temperatures remain high for sufficient duration and deeper/cooler or fast, turbulent more oxygenated water is not accessible to the fish. This phenomenon can be further exacerbated by eutrophication of rivers due to pollution - often from the use of agricultural fertilizers within the drainage basin.
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 . 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 .
Brown trout are caught by various methods which include: natural baits, spinners and wobblers, artificial flies which include nymph, wet fly, feathered lure and dry fly. They are considered to be more wary than the rainbow trout and, in a fly caster’s opinion, it is the most difficult of the species to deceive with these kinds of baits. Anglers today release many of the larger trout they catch. This makes good conservation sense, especially in high country rivers where large brown trout are highly valued.
The native range of brown trout (S. trutta) extends from northern Norway and White Sea tributaries in Russia in the Arctic ocean to the Atlas Mountains in North Africa. The western limit of their native range is Iceland in the north Atlantic ocean while the eastern limit is in Aral Sea tributaries in Afghanistan and Pakistan.
Brown trout have been widely introduced into suitable environments around the world including North and South America, Australasia, Asia, South and East Africa. Introduced brown trout have established self-sustaining, wild populations in many introduced countries. Successful introductions into the Natal and Cape Provinces of South Africa took place in 1890 and 1892 respectively. By 1909, brown trout were established in the mountains of Kenya. The first introductions into the Himalayas in northern India took place in 1868 and by 1900, brown trout were established in Kashmir and Madras.
The first introductions were in Australia in 1864 when 300 of 1500 brown trout eggs from the River Itchen survived a four month voyage from Falmouth, Cornwall to Melbourne on the sailing ship Norfolk. By 1866, 171 young brown trout were surviving in a Plenty Riverhatchery in Tasmania. Thirty-eight young trout were released in the river in 1866. By 1868, the Plenty River hosted a self-sustaining population of brown trout which became a brood source for continued introduction of brown trout into Australian and New Zealand rivers.
Brown trout occur almost everywhere in New Zealand south of Auckland. Populations in the northern North Island are limited because winter water temperatures are probably too warm for successful egg development. Although brown trout have spread to Fiordland, they have not become established on Chatham or Stewart Islands.