Lake trout (Salvelinus namaycush) is a freshwater char living mainly in lakes in northern North America. Other names for it include mackinaw, lake char (or charr), touladi, togue, and grey trout. In Lake Superior, they can also be variously known as siscowet, paperbellies and leans. Lake trout are prized both as game fish and as food fish.
Lake trout are the largest of the charrs, the record weighing almost 46.3 kg (102 lb). They were fished commercially in the Great Lakes until lampreys, overharvest and pollution extirpated or severely reduced the stocks. Commercial fisheries still exist in some smaller lakes in northern Canada.
The lake trout is a slowly growing fish, typical of oligotrophic waters. It is also very late to mature. Populations are extremely susceptible to overexploitation. Many native lake trout populations have been severely damaged through the combined effects of hatchery stocking (planting) and overharvest.
It is generally accepted that there are two basic types of lake trout populations. Some lakes do not have pelagic forage fish during the period of summer stratification. In these lakes, lake trout take on a life history known as planktivory. Lake trout in planktivorous populations are highly abundant, grow very slowly and mature at relatively small size. In those lakes that do contain deep water forage, lake trout become piscivorous. Piscivorous lake trout grow much more quickly, mature at a larger size and are less abundant. Notwithstanding differences in abundance, the density of biomass of lake trout is fairly consistent in similar lakes, regardless of whether the lake trout populations they contain are planktivorous or piscivorous.
In Lake Superior, three distinct phenotypes of lake trout persist, commonly known as "siscowet", "paperbelly" and "lean". The distinct groups operate, to some level at least, under genetic control and are not mere environmental adaptations. Siscowet numbers, especially, have become greatly depressed over the years due to a combination of the extirpation of some of the fish's deep water coregonine prey and to overexploitation. Siscowet tend to grow extremely large and fat and attracted great commercial interest in the last century. Siscowet populations have rebounded since 1970, with one estimate putting the number in Lake Superior at 100 million.
From a zoogeographical perspective, lake trout are quite rare. They are native only to the northern parts of North America, principally Canada but also Alaska and, to some extent, the northeastern United States. Lake trout have been introduced into many other parts of the world, mainly into Europe but also into South America and certain parts of Asia. In Canada, approximately 25% of the world's lake trout lakes are found in the province of Ontario. Even at that, only 1% of Ontario's lakes contain lake trout.
Lake trout have been known, very rarely, to hybridise in nature with the brook trout, but such hybrids are almost invariably reproductively sterile. Hybrids, known as "splake" are also artificially propagated in hatcheries and then planted into lakes in an effort to provide sport fishing opportunities.
The specific epithet namaycush derives from an indigenous North American name for the species, most likely in one of the Algonquian languages (c.f. Ojibwe: namegos = "lake trout"; namegoshens = "rainbow trout").