Brook trout (Salvelinus fontinalis) are part of the trout and salmon (Salmonid) family and the Char (Salvelinus) genus that include Bull Trout, Lake Trout and Artic Char.
Brook trout are native to Eastern North America, from Labrador and Newfoundland south to the southern Appalachian mountains of Georgia and South Carolina, west to Iowa and Minnesota and north to eastern Manitoba.
Brook trout require cold, clean, highly-oxygenated water. Brook trout, like other salmonids, have developed a rich life history diversity over time. This means that they have evolved the capacity to take advantage of a variety of aquatic environments. Brook trout can live in river and stream systems, tiny first order tributaries, small ponds, large lakes and estuaries. Like other trout and salmon, brook trout can migrate from fresh to salt water where they live in estuaries and the ocean close to shore, called "salters." As a char, brook trout spawn in the fall among loose gravel in streams and rivers, or on groundwater upwellings in ponds and lakes.
Because brook trout are so sensitive to water quality and water temperature, they serve as a classic "indicator" species of the larger aquatic ecosystem and the watershed draining into the water body where they live.
The reason that brook trout serve as such good "indicators" of aquatic health is that they have very specific water chemistry requirements.
Temperature
Studies have determined that brook trout cannot tolerate sustained water temperatures exceeding 77 F0 and prefer water temperatures less than 68 F0. Brook trout are less tolerant of warmer water temperatures than brown or rainbow trout. Research has documented that brook trout can migrate many miles for spawning or to find thermal refuge.
pH
This is a measure of the concentration of H+ ions in water. pH ranges from 0 (very acidic) to 14 (very basic) with 7 being neutral. Water with a pH lower than 6.0 can cause metals found in soil and rocks to dissolve in solution and suffocate and poison aquatic organisms.
Brook trout have evolved to be the most tolerant of the trout species to acidic conditions, and adult fish can tolerate pH levels as low as 5.0. However, acid mine drainage and acid deposition often produce pH levels below this threshold, and currently render lifeless thousands of miles of former brook trout streams and hundreds of lakes and ponds across the East.
DO
Brook trout require relatively high concentrations of dissolved oxygen in water compared to other fish and even other trout species. Water temperature is inversely related to dissolved oxygen concentrations, so as water warms, it holds less oxygen. In nutrient-rich systems with high biological activity (high densities of plants and algae) or where diffusion rates between water and the atmosphere are relatively slow (stagnant ponds), levels of DO can fluctuate widely over the course of 24 hours. During the day, photosynthesis produces high concentrations of oxygen, but at night photosynthesis stops and plant, algae and bacteria respiration continues to use oxygen, causing DO levels can drop to dangerously low levels. High levels of nutrients also can cause algal blooms. As algae dies, bacteria consume available oxygen as they decompose the algae, reducing oxygen levels. This is referred to as BOD or Biological Oxygen Demand.