As with so many other plants and animals found in Western North Carolina, the freshwater fish that occur here are more diverse than those found in other parts of the United States. The unique geology of the Blue Ridge Mountains and the rivers within them contributed to this wide range of fish species, as well as their distribution.
Disjointed ridges and valleys created by mountain-building activities that occurred millions of years ago separated various river drainage systems. Fish populations in these systems were either cut off from one another or entered new river basins and slowly evolved into different species.
While the term "freshwater fish" usually brings to mind such game fish as largemouth bass or sunfish, there are, in the southern Appalachians, a far greater number of small fish. These fish are well adapted to shallow, fast-running mountain creeks and tributaries. Often called minnows, and believed by many to be one type of fish species, there are, in fact, dozens of different species and subspecies, many exhibiting vividly colorful patterns.
There are several groups of small fish that many call minnows. The Cyprinid family contains, among others, minnows, shiners, dace, and chub. The Percid family includes perch but is almost entirely composed of darters. The snail darter found in the Little Tennessee River became the most famous of this group during the controversial construction of the Tellico Dam in the 1970s. It was believed that the dam would wipe out the endangered snail darter, but construction was completed nonetheless. Other snail darter populations were subsequently found in nearby drainages.
Streams are made up of different habitats, including deep, swift-flowing runs, deep quiet pools, and riffles—shallow fast-flowing currents that flow over boulders and rocks. Darters are found in riffles, bass and sunfish prefer pools, and minnows generally inhabit runs. Some minnows reach several feet in length, although the various minnows found in Western North Carolina mountain streams average only about 4 inches. About 25 species of minnows can be found in the state's mountain tributaries and rivers, including both carnivorous and herbivorous varieties.
Darters, so named for their quick movement, live and feed on the bottom of streams and are not easy to spot from above the surface. There are more than 20 species that occur in Western North Carolina, some restricted to small areas.
Ichthyologists, those who study the fishes, believe that populations of various darters and minnows were separated or combined by stream capture. The rivers flowing to the Atlantic have eroded faster than those flowing into the Mississippi basin, and at various times in the past, the eastern-flowing rivers have intercepted the headwaters of westward flowing rivers, thus capturing those streams. This interception may have influenced differences in such species as the turquoise, sea green, and Swannanoa darters. That all three species are similar implies that this separation occurred relatively recently.