The sheepshead minnow is a small, thick-bodied fish with a high, arched back and a flat-topped head.  These fish are found in shallow, brackish inlets, often in the company of mummichogs and silversides.  Sheepshead minnows can be immediately distinguished from mummichogs by their thicker body shape, which is nearly half as tall as it is long, and by their thick, square tails.  The body and head are covered with large round scales, and its small mouth holds large, wedge-shaped teeth with tricuspid cutting edges.

Male sheepshead minnows, on average, are larger than females.  The male has a black bar along the square edge of its thick tail, while the female has an obvious dark spot on the back of the dorsal fin.  During the spawning season, male sheepshead minnows become an iridescent blue with a dark orange belly.  Young sheepshead minnows are more slender than adults and have irregular bands on their sides.

The sheepshead minnow is omnivorous, feeding on plants, invertebrates, and other fish.  They are quite aggresive and can injur and kill fish much larger than themselves by repeatedly slashing a victim with its sharp teeth.

During the winter months, sheepshead minnows will burrow in the mud, lying dormat during the cold weather.

Found in salt marshes, sheepshead minnows have a high resistance to environmental extremes.  Like mummichogs, they can withstand changing levels in oxygen, temperature, and salinity conditions that are commonplace in coastal salt marshes.  Sheepshead minnows are often used as bait in recreational fishing.