<P> Global climate change is also of concern . S. trutta morpha fario prefers well - oxygenated water in the temperature range of 60 to 65 ° F (16 to 18 ° C). S. trutta bones from an archaeological site in Italy, and ancient DNA extracted from some of these bones, indicate that both abundance and genetic diversity increased markedly during the colder Younger Dryas period, and fell during the warmer Bølling - Allerød event . </P> <P> Cover or structure is important to trout, and they are more likely to be found near submerged rocks and logs, undercut banks, and overhanging vegetation . Structure provides protection from predators, bright sunlight, and higher water temperatures . Access to deep water for protection in winter freezes, or fast water for protection from low oxygen levels in summer are also ideal . Trout are more often found in heavy and strong currents . </P> <P> The brown trout is a medium - sized fish, growing to 20 kg (44 lb) or more and a length of about 100 cm (39 in) in some localities, although in many smaller rivers, a mature weight of 1.0 kg (2.2 lb) or less is common . S. t . lacustris reaches an average length of 40--80 cm (16--31 in) with a maximum length of 140 cm (55 in) and about 60 pounds (27 kg). The spawning behaviour of brown trout is similar to that of the closely related Atlantic salmon . A typical female produces about 2,000 eggs per kg (900 eggs per lb) of body weight at spawning . On September 11, 2009, a 41.45 - lb (18.80 - kg) brown trout was caught by Tom Healy in the Manistee River system in Michigan, setting a new state record . As of late December 2009, the fish captured by Healy was confirmed by both the International Game Fish Association and the Fresh Water Fishing Hall of Fame as the new all - tackle world record for the species . This fish now supplants the former world record from the Little Red River in Arkansas . </P> <P> Brown trout can live 20 years, but as with the Atlantic salmon, a high proportion of males die after spawning, and probably fewer than 20% of anadromous female kelts recover from spawning . The migratory forms grow to significantly larger sizes for their age due to abundant forage fish in the waters where they spend most of their lives . Sea trout are more commonly female in less nutrient - rich rivers . Brown trout are active both by day and by night and are opportunistic feeders . While in fresh water, their diets frequently include invertebrates from the streambed, other fish, frogs, mice, birds, and insects flying near the water's surface . The high dietary reliance upon insect larvae, pupae, nymphs, and adults allows trout to be a favoured target for fly fishing . Sea trout are fished for especially at night using wet flies . Brown trout can be caught with lures such as spoons, spinners, jigs, plugs, plastic worm imitations, and live or dead baitfish . Freshwater brown trout range in colour from largely silver with relatively few spots and a white belly, to the more well - known brassy brown cast fading to creamy white on the fish's belly, with medium - sized spots surrounded by lighter halos . The more silver forms can be mistaken for rainbow trout . Regional variants include the so - called "Loch Leven" trout, distinguished by larger fins, a slimmer body, and heavy black spotting, but lacking red spots . The continental European strain features a lighter golden cast with some red spotting and fewer dark spots . Notably, both strains can show considerable individual variation from this general description . Early stocking efforts in the United States used fish taken from Scotland and Germany . </P>

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