Technically the brook trout is a char, more closely related to bull trout than to rainbows or cutthroats. They are not a native species in Idaho. The limit is high because brook trout are very prolific and tend to out-compete and interbreed with the other trout species, including the native bull trout, a federally listed species. Brook trout can be a significant threat to fishing opportunity for native cutthroat trout. They also tend to become stunted when over-crowded in lakes, and they are difficult to remove once established.