- Written by Clyde McMillan-Gamber Clyde McMillan-Gamber
Johnny darters, black-nosed dace, and banded killifish live in clear, flowing brooks and streams in southeastern Pennsylvania, as elsewhere in the eastern United States.
The crystalline water of these small waterways tumbles over and around rocks and allows us to see down to their stony or mud bottoms.
Each species of these fish is about 2 inches long as adults and streamlined to cope with currents in those waterways. And each kind is mostly brownish, which blends them into their habitats of gravel or mud bottoms. I see their dark shadows on waterway bottoms better than the fish themselves.
When plate tectonics in the Earth heave the land up, gravity pulls water downhill, creating waterways, which are then filled with rain. Running water carves channels in the ground that transport the water.
These species of small fish generally live in the slower, deeper “holes” of each small waterway where the current is slower. There the fish can watch for invertebrates and plant material in the water with minimal swimming, saving energy.
These kinds of fish enjoy reduced competition for food because they inhabit different parts of the waterways, though there is some overlap.
With no air bladders to allow them to swim in mid-depth, darters get food among rocks on stream bottoms. Dace generally grab food from the middle depth, while killifish obtain it mostly on its surface.
Several kinds of critters find and eat some of these small fish in spite of their camouflage. Some of those animals are trout, a variety of herons, belted kingfishers, and water snakes. Crayfish consume the eggs of these small fish spawned in shallow water.
Individual darters swim in short bursts along stream bottoms and quickly slip between rocks to hide. Their brown-and-dark-streaked bodies blend well there as they watch for invertebrates to eat.
Little schools of dace swim in mid-stream. Each of these fish has a black stripe on each flank from its mouth back to the base of its tail. Male dace in June have attractive, orange fins and an orange streak along the dark one on each flank to exhibit their breeding readiness.
Schools of killifish are yellowish-brown like the mud-bottom waterways they prefer. They also have several vertical, darker stripes along each flank that helps camouflage them.
These streamlined, camouflaged fish help make clear waterways more interesting to us and feed several kinds of predatory animals. They are a major, pretty part of crystalline streams and brooks.
Clyde McMillan-Gamber is a retired Lancaster County Parks naturalist.