Physical Characteristics
Shaped like a salmon, the rainbow trout has highly variable coloration although it's generally described as silvery with dark-green on the back, where it has numerous spots. Sometimes flecks of metallic pink occur on its side and head. The bull trout on the other hand has no black spots on its dorsal fin, and its large head and jaws are distinctly out of proportion to the rest of its body. It has pale yellow spots along the back and red or orange spots along its side. The weight and length of both types of trout vary tremendously depending on habitat.
Conservation Status
The bull trout is listed as a threatened species under the U.S. Endangered Species Act, meaning it's likely to become endangered within the foreseeable future throughout all or a significant portion of its range. Deliberately fishing for bull trout is illegal, and fishermen are advised to release any catch immediately. For the rainbow trout, the situation isn't as dire. Although it is suffering increasing habitat loss owing to human factors such as water pollution, it breeds easily in hatcheries, and the young are then used to restock rivers and lakes.
Classification
Both the bull and rainbow trout are classified as Salmonidae under the order Salmoniformes, which includes salmon, trout, chars, freshwater whitefishes and graylings. The difference is that the bull trout is also recognized as Salvelinus, a genus of salmonid fish, which means it is actually a char rather than a trout. This genus also includes brook trout, lake trout and dolly varden trout, among others.
Range
Both trout types prefer the cool waters of the Northern Hemisphere, but the bull trout is found only west of the Continental Divide in Montana. The rainbow trout, on the other hand, is native to the Pacific Coast of North America from Alaska to Mexico. In addition, it is stocked over much of the United States. Unlike the rainbow trout, the bull trout inhabits an entire river system from the mainstem to all the tributaries.