July 1915. The trout weighed only because, at the time of weighing, it was badly decomposed after 21 days in the bush without refrigeration. A brook trout, caught in October 2006 in Manitoba, is not eligible for record status since it was released alive. This trout weighed about based on the accepted formula for calculating weight by measurements, and it currently stands as the record brook trout for Manitoba. Artificial propagation and aquaculture 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. Brook trout are also raised commercially and sold to angling organizations or groups to stock their lakes or ponds. Some businesses hold a "U-fish license" where the public can fish at their lake or pond and buy the fish they catch. Commercial fisheries do not commonly raise brook trout because they do not grow as fast as other types of fish. Brook trout raised commercially are often kept in large circular tanks with a constant water flow going through them. This allows for a current to circulate through the tank and keep it clean, acting as a flush of water that takes fish waste with it. Some more elaborate systems operate on a re-circulation system where the water is filtered and reused. The fish are typically fed a pelleted food consisting of 40–50% protein and 15% fat. The fish food is usually made from fish oil, animal protein, plant protein and vitamins and minerals. The protein is often sourced from soy beans. Conservation status 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. If already stressed by overharvesting or