The tail fin will also serve as an identifying characteristic as it is square or very shallowly forked. The teeth on the roof of the mouth are confined to only a small cluster near the front and do not occur along its length as in the Atlantic salmon, brown trout, and rainbow trout. Juvenile brook trout are very similar in coloration to young Atlantic salmon. Both have dark and light alternating vertical bars, and the spots on the side are not pronounced in the brook trout. The distinction is the forked verses the squarish tail and the upper teeth in the brook trout.
Brook trout are cold water fish.
It is more rigid in its temperature requirements than rainbow or brook trout and as a rule will not be found in streams where 68 degrees F are exceeded for an extended amount of time. Temperatures above 77 degrees F are fatal if sustained for a prolonged period of time. In lakes and ponds with higher temperatures where brook trout are found usually cold water springs or other sources of cold water are near by. The brook trout spawns in late summer or autumn depending on temperature and latitude. Through the southern reaches it spawns during September, October, or November, but it may take place as early as August in northern Canada and as late as December in the south.