Fish
Fantail Darter
Etheostoma flabellare · also called fantail darters
Beneath a flat streambed rock, a male fantail darter fans a cluster of eggs glued upside down to the stone above him, small fleshy knobs on his dorsal fin doing double duty as a possible decoy for passing females.
Overview
The fantail darter, Etheostoma flabellare, is a small darter native to rocky, moderately flowing stream habitat across the eastern and central United States. Its upside-down nest placement and egg-mimicking fin knobs on breeding males make it one of the more behaviourally distinctive members of a genus already full of unusual small fish.
A nest built on the ceiling
Where most stream fish either scatter their eggs or bury them in gravel, the fantail darter glues its entire clutch to the underside of a rock, turning the roof of a small stone cavity into a nursery the male defends until every egg hatches.
Status
Least Concern — widespread and stable across suitable stream habitat throughout the eastern and central United States.
Fantail Darter: common questions
What are the knobs on a male fantail darter's fin for?
Breeding male fantail darters develop small, fleshy knobs on the tips of their spiny dorsal fin rays, a feature some researchers believe may mimic fish eggs, potentially helping attract females toward an already-occupied nest site by suggesting successful spawning has already taken place there.
Why does the fantail darter lay its eggs upside down?
A female fantail darter attaches her eggs to the underside of a flat rock rather than the stream bottom, meaning the eggs end up hanging from the roof of the nest cavity, a positioning that keeps them away from settling sediment and easier for the guarding male to fan and defend.
Does the male fantail darter guard the nest alone?
Yes, a male fantail darter guards the chosen nest cavity beneath its rock until the eggs hatch, fanning water over the developing eggs to keep them oxygenated and driving off potential egg predators without any direct involvement from the female after spawning.
Why is the fantail darter found in a wider range of streams than some other darters?
The fantail darter is somewhat more tolerant of moderate stream disturbance and varied water conditions than many other darter species, a relative hardiness that allows it to persist across a broader range of stream habitat than its more sensitive relatives, such as the greenside darter or rainbow darter.