Darters are among the most ecologically important fishes found in found in the streams of the midwest. In many sections of stream up to a third of all fish species will be some kind of darter. But most fishermen that wade and fish these same streams know little or nothing about them.
Darters are also an important piece of that big puzzle we are always trying to put together when we are out on the water. So here is a mini primer on these cool little fish.
Each species of darter has evolved to occupy a specific slot or niche in the food chain. That is why there are often several species in the same section of riffle. Some may occupy bigger rocks and rubble than others. Some species may live in more current or shallower or deeper water than other species. In my favorite river, the Little Miami, there are a dozen species alone. Darters prey on insects and crustaceans, and in turn are preyed on by species such as smallmouth bass and saugeye. Darters are an indispensable link in the food chain. The presence of darters in a stream reflects good water quality and diversity of healthy habitats.
A darter is built to maneuver in, around and under rocks and gives it an advantage as a bottom forager. Fast swift riffles provide protection for darters because few predators can live there and must move in and out even if they do forage there. In nature, it is usually true that "form follows function." Many darters do not even possess a swim bladder. This lack of buoyancy allows them to stay near the bottom in swift currents. Many bottom-dwelling darters possess flattened, downward-sloping heads. This feature lets them take advantage of water flowing to help plane or push down on the fish's head, thereby helping the fish to remain near the bottom. Some darter species that live at mid-water depths do possess a swim bladder to help them remain suspended in the water column.
Darters are small. However, there is considerable variation in length among the species found in our rivers, anywhere from an inch or so up to six inches long.
What darters eat varies with the lifestage of the fish. Juvenile darters chomp on small crustaceans such as water fleas, plankton and zooplankton . Adults prefer midge larvae, blackfly larvae, mayflies and caddisflies. Larger darters species may also eat amphipods freshwater shrimp, isopods sowbugs and crayfish. Darters do not compete with most minnow species because the minnows often occupy the upper levels of the water column. Food availability and water velocity help to determine the activity levels of darters' foraging. For example, in pools or areas of slower current, darters range farther to procure food. Similarly, when flow rates are high, travel is reduced. The presence of large crayfish which will prey on darters as well as predatory fish such as smallmouth bass will affect how much darters move also. It turns out that in nature crayfish, while smallmouth prey themselves, benefited from darters being forced to hide underneath the rocks to avoid smallmouth predation. While at the same time the crayfish crawling around hunting in the rocks evicted the darters which made them become more active and available for smallmouth to prey upon. At the same time big darters will eat small crayfish, It is, as the saying goes a fish eat fish world down there.
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