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(Mitchill, 1814) 
(Mitchill, 1814) 
The brook trout (Salvelinus fontinalis), sometimes called the eastern brook trout, is a species of fish in the salmon family of order Salmoniformes. In many parts of its range, it is known as the speckled trout or squaretail. A potamodromous population in Lake Superior is known as coaster trout or, simply, as coasters. Though commonly called a trout, the brook trout is actually a char, along with lake trout, bull trout, Dolly Varden and the Arctic char. The brook trout is the state fish for eight states: Michigan, New Hampshire, New Jersey, New York, Pennsylvania, Vermont, Virginia and West Virginia
The brook trout inhabits small streams, creeks, lakes, and spring ponds. Some brook trout, referred to as sea-run brook trout, are anadromous. One study showed that sea-run brook trout were longer, heavier, and had higher carbon to nitrogen ratios (indicator of carbon content) than equivalent resident trout. This relationship shows that offspring of sea-run trout could have potential adaptive advantages over resident offspring  Brook trout are native to a wide area of eastern North America, but increasingly confined to higher elevations southward in the Appalachian Mountains to northern Georgia, Canada from the Hudson Bay basin east, the Great Lakes–Saint Lawrence system, and the upper Mississippi River drainage as far west as eastern Iowa.
The typical pH range of brook trout waters is 5.0 to 7.5, with pH extremes of 3.5 to 9.8 possible. Water temperatures typically range from 34 to 72°F (1 to 2 °C). Warm summer temperatures and low flow rates are stressful on brook trout populations—especially larger fish. This trend shows a connection between season-specific survival and future problems associated with climate change.
This species is green to brown in basic colour, with a distinctive marbled pattern (called vermiculations) of lighter shades across the flanks and back and extending at least to the dorsal fin, and often to the tail. A distinctive sprinkling of red dots, surrounded by blue haloes, occur along the flanks. The belly and lower fins are reddish in color, the latter with white leading edges. Often, the belly, particularly of the males, becomes very red or orange when the fish are spawning. The species reaches a maximum recorded length of 86 cm (33 in) and a maximum recorded weight of 6.6 kg (14.5 lb). It can reach at least seven years of age, with reports of 15 year old specimens observed in California habitats to which the species has been introduced. Typical lengths vary from 25 to 65 cm (10 to 26 in), and weights vary from 0.3 to 3.0 kg (0.7 to 7.0 lb). Growth rates are dependent on season, age, water and ambient air temperatures, and flow rates. In general flow rates affect the rate of change in the relationship between temperature and growth rate. For example in spring growth increased with temperature at a faster rate with high flow rates than with low flow rates.
S. fontinalis prefers clear waters of high purity and a narrow pH range in lakes, rivers, and streams, being sensitive to poor oxygenation, pollution, and changes in pH caused by environmental effects such as acid rain. Its diverse diet includes crustaceans, frogs and other amphibians, insects, molluscs, smaller fish, invertebrates, and even small aquatic mammals such as voles. It provides food for seabirds and suffers attack by lampreys. The brook trout is a short-lived species, rarely surviving beyond four or five years in the wild.
Individuals normally spend their entire lives in fresh water, but some—colloquially called "salters" or "sea-run"—may spend up to three months at sea in the spring, not straying more than a few kilometres from the river mouth. The fish return upstream to spawn in the late summer or autumn. The female constructs a depression in a location in the stream bed, sometimes referred to as a "redd", where groundwater percolates upward through the gravel. One or more males approaches the female, fertilizing the eggs as the female expresses them. A majority of spawnings involve peripheral males which directly influences the amount of eggs that survive into adulthood. In general the larger the number of peripheral males present the more likely the eggs will be cannibalized. The eggs are slightly denser than water. The female then buries the eggs in a small gravel mound; they hatch in 95 to 100 days.
A potamodromous population of brook trout native to Lake Superior, which run into inflowing rivers to spawn, are called "coasters". Coasters tend to be larger than most other populations of brook trout, often reaching 2–3 kg in size. Many coaster populations have been severely damaged by overfishing and habitat alterations, especially by the construction of hydroelectric power dams, on their inflowing streams. In Ontario and Michigan, efforts are underway to restore and recover coaster populations.
The possibility of hydrofracking in several states could have lasting implications on brook trout populations. Hydrofracking could put a substantial strain on fresh water supply which could affect water levels in brook trout habitat. Building of infrastructure and transportation in relation to hydrofracking would also impact water and habitat quality for brook trout. Finally, the leaching of waste water from wells could affect water quality and chemistry in brook trout habitat.
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The brook trout is a popular game fish with anglers, particularly fly fishermen. Today, many anglers practice catch-and-release tactics to preserve remaining populations, and organizations such as Trout Unlimited have been in the forefront of efforts to institute air and water quality standards sufficient to protect the brook trout. Revenues derived from the sale of fishing licenses have been used to restore many sections of creeks and streams to brook trout habitat. Brook trout are also commercially raised in large numbers for food production, being sold for human consumption in both fresh and smoked forms. Because of its dependence on pure water and a variety of aquatic and insect life forms, the brook trout is also used for scientific experimentation in assessing the effects of pollution and contaminated waters.
Partially as a result of its popularity as a game fish, the brook trout has been introduced in some areas to which it was not originally native, and has become established widely throughout the world. In some parts of the world, it has had a harmful effect on native species, and is a potential pest.
Brook trout can sometimes hybridise with other species, both natural and artificial hybrids are known. Native populations of bull trout (S. confluentus) are in danger of hybridization with introduced brook trout in the Pacific Northwest.
One such intergeneric hybrid, between the brook trout and the brown trout (genus Salmo) is the tiger trout. Tiger trout occur very rarely naturally, but are sometimes artificially propagated. Such crosses are almost always reproductively sterile. They are popular with many fish stocking programs because they can grow quickly, and may help keep rough fish populations in check due to their highly piscivorous (fish-eating) nature.
A less frequent natural hybrid is the splake, a hybrid between the brook trout and lake trout. Although uncommon in nature, some jurisdictions artificially propagate splake in substantial numbers for stocking into brook trout or lake trout habitats. An example would be in Ontario, where both F1 splake and the lake trout backcross have been planted for several years. The backcross is the result of an F1 splake male being crossed with a female lake trout (i.e., 75% lake trout and 25% brook trout).
Although splake were first described in 1880, Ontario began experimenting with the hybrids in the 1960s in an effort to replace collapsed lake trout stocks in the Great Lakes. Due to mediocre results, the experiment never really progressed beyond Georgian Bay. The theory was that splake would grow more quickly and mature sooner than lake trout with the hope that they would be able to reproduce before being attacked by the invasive sea lamprey. Unfortunately, although splake are relatively unusual among hybrids in that they are fertile, fertility in nature is behaviourally problematic—very few natural progeny are produced by introduced splake populations.
After some experimentation in the late 1970s, stocking in the Great Lakes and, especially, in Georgian Bay, was converted entirely to the so-called lake trout backcross in the early 1980s. Although the backcross program did succeed in creating some localised angling opportunities, it never achieved any degree of success in terms of natural reproduction—the backcross was only marginally better at reproducing than was the F1 splake. The F1 splake has proved to be a success, however, in providing angling opportunities in smaller lakes and most of the planting of splake in Ontario now goes to those situations. In the first of two cases, former brook trout waters which have become infested with spiny-rayed fish to the point where they no longer produce brook trout are stocked with splake. The splake grow more quickly than do wild-strain brook trout and become piscivorous at a younger age and, hence, are more tolerant of competitors than are brook trout. In the second case, relatively small lake trout lakes that experienced poor recruitment due to insufficient deep-water juvenile lake trout habitat will support fairly good splake fisheries, since splake are less dependent on extreme deep water than are the lake trout and they grow more quickly, providing a better return to anglers. In both cases, due to the behavioural sterility of splake, all such fisheries are entirely dependent on artificial propagation.
Brook trout populations depend on cold, clear, well-oxygenated water of high purity. As early as the late 19th century, native brook trout in North America became extirpated from many watercourses as land development, forest clear-cutting, and industrialization took hold. Streams and creeks that were polluted, dammed, or silted up often became too warm to hold native brook trout, and were colonized by transplanted smallmouth bass and perch or other introduced salmonids such as brown and rainbow trout. The brown trout, a species not native to North America, has replaced the brook trout in much of the brook trout's native water. Brook trout populations, if already stressed by overharvest or by temperature, are very susceptible to damage by the introduction of exogenous species. Many lacustrine populations of brook trout have been extirpated by the introduction of other species, particularly percids, but sometimes other spiny-rayed fishes.
In addition to chemical pollution and algae growth caused by runoff containing chemicals and fertilizers, air pollution has also been a significant factor in the disappearance of brook trout from their native habitats. In the United States, acid rain caused by air pollution has resulted in pH levels too low to sustain brook trout in all but the highest headwaters of some Appalachian streams and creeks. Brook trout populations across large parts of eastern Canada have been similarly challenged; a subspecies known as the aurora trout was extirpated from the wild by the effects of acid rain.
Today, in many parts of the range, efforts are underway to restore brook trout to those waters that once held native populations, stocking other trout species only in habitats that can no longer be recovered sufficiently to sustain brook trout populations.
The current world angling record brook trout was caught by Dr. W. J. Cook on the Nipigon River, Ontario, in July 1915. The 31 inch (79 cm) trout weighed only 14.5 lbs (6.6 kg) because, at the time of weighing, it was badly decomposed after 21 days in the bush without refrigeration. This is the longest-standing angling world record. A 29 inch (74 cm) brook trout, caught in October 2006 in Manitoba, is not eligible for record status since it was released alive.