Rainbow trout and brown trout are two widely recognized freshwater game fish. These distinct species often coexist, yet possess unique characteristics. Their widespread distribution and popularity contribute significantly to recreational angling and the ecological balance of many freshwater systems.
Visual Identification
Distinguishing rainbow and brown trout begins with their coloration and spot patterns. Rainbow trout display an iridescent pink or red stripe along their lateral line, from gill plate to tail. Their bodies are adorned with numerous small, dark spots, also present on their dorsal and caudal fins. In contrast, brown trout exhibit a body color ranging from buttery-yellow to olive-brown, marked with dark spots and often red or orange spots surrounded by pale halos.
The tail fin provides another clear differentiator. A rainbow trout’s caudal fin is broad and covered in small, distinct black spots. Brown trout, however, have a tail fin that is unspotted or features only a sparse scattering of spots, and its shape tends to be more square or slightly forked.
The maxillary bone can also be helpful. In rainbow trout, this bone does not extend beyond the back edge of the eye. In larger brown trout, it often extends noticeably past the eye. Additionally, brown trout fins sometimes display a subtle white or orange leading edge, a feature less common on rainbow trout.
Habitat and Geographic Range
These trout species have distinct native ranges. Rainbow trout are indigenous to the Pacific drainages of North America, from Alaska to northern Mexico. Brown trout originated in Europe and Western Asia, thriving in various freshwater systems. Both species have since been extensively introduced worldwide, establishing populations in diverse aquatic environments.
Brown trout tolerate warmer water and slightly lower oxygen levels than rainbow trout. Rainbow trout prefer colder, clearer, and more oxygenated waters, often found in fast-flowing rivers and streams. Rainbow trout hold positions in faster currents and riffles, where oxygen levels are higher. Brown trout seek refuge under submerged logs, undercut banks, and in deeper, slower-moving pools for cover and ambush.
Behavioral and Feeding Differences
Dietary habits distinguish these two trout species, though both are opportunistic feeders. Rainbow trout diets consist predominantly of aquatic and terrestrial insects, small crustaceans, and other invertebrates. Larger brown trout, particularly those over 15 inches, are more piscivorous, meaning their diet includes a higher proportion of smaller fish like sculpins, dace, or other trout. They also consume crayfish, amphibians, and occasionally small rodents.
Rainbow trout are more aggressive and willing to strike a lure or fly, making them accessible to anglers. Brown trout are more cautious and wary, often exhibiting a nocturnal feeding pattern, especially for larger individuals. This wariness makes them a challenging target. When hooked, rainbow trout are known for acrobatic leaps and fast, powerful runs. Brown trout fight deeper, employing strong headshakes and bulldog-like resistance.