Freshwater Drum/Sheepshead (Aplodinotus grunniens)

(c) MN DNR, C. Iverson

Fish of the Mississippi River

Introduction

The freshwater drum is a fish known for its noise. Males make a grunting or rumbling sound during the breeding season, which is thought to attract females. That noisiness generated many colorful nicknames, including croaker, thunder pumper, grunter, grinder, bubbler. Other names include silver bass, gray bass, lavender bass, and gaspergou from the French casse-burgeau "to break a clam." Locally many anglers refer to them as "sheepshead."

Freshwater drum like turbid water and inhabit slow or moderate current over sand or mud bottoms. A freshwater drum’s lateral line (a visible line of sense organs on the side of a fish for detecting pressure and vibration) extends to the end of its tail, which is farther than most other fish species. This adaptation allows the drum to pick up vibrations in the water and better locate food and enemies. It feeds on many different types of food from crustaceans and seeds to minnows and aquatic insects. It can use its high snout and forehead to flip stones and expose food.

Fascinating Facts

• Male freshwater drum makes its unique sound with muscles rubbed along its swim bladder. Anglers may be surprised to feel them vibrate like a cell phone.
• Native Americans strung together the freshwater drum’s large otoliths (granules of calcium carbonate) as necklaces or bracelets. All vertebrates have ototliths in the inner ear but the freshwater drum’s can be an inch in diameter. The otolith help fish stay balanced and oriented in murky water.
• Freshwater drum's eggs float on the water surface until they hatch, sometimes traveling for miles on rivers or windswept lakes before the tiny fry (newly hatched fish) emerge.
• Freshwater drum is the only member of its family in North America to occur completely in freshwater habitats.
• There is some indication that this fish, with its big molar-like crushing teeth, may be learning to eat zebra mussels.

Identification

Key ID Features: Freshwater drum average 10-14 inches in length. It has a humped back with a long, sloping forehead and white lips. Coloration is gray with purple/bronze reflection and rounded triangular tail.
Present in Park: Commonly found in the Mississippi River. It is one of the most often caught fish in our fishing programs.
Habitat: Primarily in large rivers and shallow lakes that have mud or sand bottoms
MN Status: Present

For Further Reading

Minnesota Department of Natural Resources. 2017. “Freshwater Drum.” Accessed May 8. http://www.dnr.state.mn.us/fish/freshwaterdrum.html