The freshwater drum (Aplodinotus grunniens) belongs to the order Perciformes and family Sciaenidae; it is the only freshwater member of the family. Freshwater drum are endemic to freshwater environs of the Americas, and their distributional range extends as far north as the Hudson Bay of Canada and reaches as far south as the Usumacinta River Basin of Guatemala. In the United States, eastward distribution includes the eastern Appalachians westward as far as Kansas, Oklahoma, and Texas. This fish appears to have the greatest latitudinal range of any freshwater fish in North America. In Arkansas, A. grunniens occurs throughout the state but mainly is found in the larger lakes and rivers.
The closest living relatives of A. grunniens are a group of marine genera including the spotfin croaker (Roncador) and red drum (Sciaenops). The black drum (Pogonias cromis), which occurs in the western Atlantic Ocean, is a sister taxon.
This fish was given its name because of the loud, booming croaks that mature males (at least three years old) make by contracting muscles along their air bladder walls. Although the purpose of the grunting has yet to be proven, only mature males make the sound, so it is assumed to be linked to spawning activities. For example, drumming sounds become more frequent and longer as breeding reaches its peak and they gradually diminish through the summer and completely cease in late August. Commercial fishermen as well as anglers have given A. grunniens several colloquial names, including gaspergou (in Louisiana), grunter, and sheepshead.
One of the first reports of a freshwater drum in North America was in 1774 by the ethnographer, historian, and naturalist Antoine-Simon Le Page du Pratz (1695–1775) in his 1758 History of Louisiana, where he reported “burgobreaker” (freshwater drum) that fed on mollusks by crushing them with their pharyngeal teeth. Additionally, fishes recovered from digs at archaeological sites of the Red River Caddo (dated from AD 1050 to 1750) included freshwater drums. The freshwater drum was described in 1819 by Constantine Samuel Rafinesque (1783‒1840).
The freshwater drum prefers deep pools and backwaters of medium to large rivers and reservoirs with sluggish current. It appears to prefer clear water, but it is also tolerant of turbid and murky water. They are bottom-feeders on clean sand and gravel substrates, where they eat a variety of prey, including bivalve mollusks, chironomids, small crustaceans, crayfish, other aquatic macroinvertebrates, and small fishes (mostly various shad species and small freshwater drum). In addition, because of their heavy pharyngeal molar-like crushing teeth, A. grunniens have been reported to prey upon various bivalves, including nuisance zebra mussels (Dreissena polymorpha) in the northern part of their range, but they are apparently not halting the spread of this invasive species.
Freshwater drum are dusky gray to silvery deep-bodied humpbacked fishes with a white belly; a blunt snout; a subterminal mouth; and a long, divided dorsal fin with ten (nine anterior, one posterior) stiff spines and twenty-six to thirty-two soft rays. The scales of A. grunniens are of the ctenoid type, and the lateral line scales range from forty-nine to fifty-three. One unusual character of this fish is that its lateral line extends into its dorsal fin. The average drum weighs about 2.3 to 6.8 kg (5–15 lbs.), and females are larger than males. A world record specimen was caught in 1972 from Nickajack Lake in eastern Tennessee and weighed 24.7 kg (54 lbs., 8 oz.). In Arkansas, a record freshwater drum was caught in 2004 on Lake Wilson (Ashley County) and weighed 20.6 kg (45 lbs., 7 oz.).
Freshwater drum serve as forage fish to several species of predatory fish during their first year of development, including walleye, bass, and pike. Thereafter, gulls and humans are the primary predators. They are important in commercial fisheries on the Mississippi River, although the market price is quite low compared to other fishes. Up to 453,000 kg (one million lbs.) of A. grunniens are harvested each year in some localities. In Arkansas, from 1975 and 1981, between 200,000 kg (441,000 lbs.) and 470,000 kg (1,000,000 lbs.) of freshwater drum were taken by commercial fishermen yearly from Arkansas River systems. Freshwater drum are strongly nocturnal, and most are harvested or caught by angling at night, although some are even taken by bow-fishing.
In general, spawning occurs in the summer as freshwater drum move into warmer, shallower waters that are usually less than 10.0 m (33.0 ft.) deep. They typically spawn during a six- to seven-week period in early to mid-summer (June to July) when the water temperatures reach about 18 to 20°C (65 to 67°F). However, spawning in Arkansas has been reported to occur in late spring (April or May) when adults move out of rivers and reservoirs into tributaries. During the spawning run, females release their eggs into the water column, followed by the males releasing their sperm. Females have a tremendous fecundity, with clutch sizes averaging 40,000 to 60,000 but as high as over half a million eggs; however, many eggs are prone to predation. Freshwater drum are pelagic spawners but give no parental care to their larval spawn. Following fertilization, the eggs are buoyant and float to surface. They stay attached to the surface film for one to two days, and hatch in another twenty-four to forty-eight hours. Many eggs and larvae are predated upon hatching. Small pre-larvae average 3.2 mm (0.13 in.) in length, and the post-larval stage begins about two days after hatching, at which point they reach a length of 4.4 mm (0.17 in.). Once they are about 25.0 mm (1.0 in.) long, they move to deeper waters and eventually assume their normal lifestyle of bottom-dwelling.
A. grunniens are known to be long-lived among native freshwater fishes. The average age of a freshwater drum is between six and thirteen years, although some have lived into a seventh decade.
On December 29, 2010, about 100,000 A. grunniens were found dead on the banks of the Arkansas River in Arkansas. The fish kill covered 27.4 km (17.0 mi.) of river from the Ozark-Jetta Taylor Lock and Dam (Franklin County) downstream to River Mile 240, south of Hartman (Johnson County). Examination and testing of these fish determined that the most likely cause of the kill was gas bubble trauma when the spillways were opened on the Ozark Dam. Concerning conservation, A. grunniens do not require significant protection or major management, monitoring, or research actions.
Freshwater drum have been reported to harbor over sixty-six taxa of parasites, including protozoans, monogenes, trematodes, cestodes, nematodes, acanthocephalans, leeches, mollusks, and crustaceans. As of 2018, none of these parasites have been reported from Arkansas populations of A. grunniens.
For additional information:
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Chris T. McAllister
Eastern Oklahoma State College
Last Updated: 12/11/2018