The bigmouth buffalo, Ictiobus cyprinellus, also known as the gourd head, redmouth buffalo, buffalo fish, bernard buffalo, roundhead, or brown buffalo, is the largest species of the Catostomidae or "sucker" family.
The bigmouth is a dull brownish olive color with dusky fins. Like other suckers it has a long dorsal fin, but unlike others it has a large oblique and terminal mouth. It is the largest of the buffalo fish and reaches a length of more than 4 ft (1.2 m) and 65 lb (29 kg) in weight.
It migrates upstream to spawn in the spring, usually April to June where it lays its eggs on plants to which they adhere. Bigmouth buffalo, unlike its close relatives the black and smallmouth buffalos, is a filter-feeder, using its very fine gill rakers to strain crustacean zooplankton from the water. It sometimes feeds near the bottom, using short up-and down movements to swirl the water and thus be able to filter from the water the plants and animals that hover near the bottom or rest lightly on it, including small crustaceans, insects, and other invertebrates. More than one male will assist in spawning by moving the female to the top of the water to help mix eggs and milt. Spawn is usually April–May.
The fish is vulnerable in shallow water and is often captured by spearing. It is commercially caught on trot lines, setlines, hoop and trammel nets, and seines. Though it has numerous small bones, its good flavor makes it one of the most valuable of the non-game freshwater fish.
They generally live in shallow lakes, large slow-moving rivers or swamps since they seem to be adept at dealing with these low oxygen type habitats.
The bigmouth's native and introduced distribution is confined to the countries of Canada and the United States of America. In Canada they inhabit the Milk River. In the United States they are native to Iowa, South Dakota and Minnesota, and more southern states include eastern Texas and Oklahoma. Among other reservoirs and waterbodies, the major drainages they are found in include Lake Erie, Ohio River and the Mississippi River.