The bigmouth buffalo, Ictiobus cyprinellus, also known as the gourd head, redmouth buffalo, buffalo fish, bernard buffalo, roundhead, or brown buffalo, is a large species of the Catostomidae or "sucker" family.
The bigmouth buffalo 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 is distributed from the Red River of the North, Manitoba, Canada and North Dakota, United States to the Ohio River and south in the Mississippi River system to Texas and Alabama in the United States. It lives in sluggish areas of large rivers and shallow lakes and streams.
The bigmouth buffalo 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 (Pflieger 1997). 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.
This is a description of a monitoring plan for the bigmouth buffalo, Ictiobus cyprinellus, and a short life history of the fish and previous management done. The bigmouth buffalo is naturally found throughout the United States from the Great Lakes south to Alabama and Louisiana drainages and west to Texas and Minnesota. They generally live in shallow swells, large slow-moving rivers or swamps since they seem to be adept at dealing with these low oxygen type habitats. This species of buffalo spawn in rock and gravel (open substratum) and have pelagic free embryos which they lay sometime in the spring. Populations of the bigmouth buffalo are currently shown as stable. The bigmouth buffalo is a popular foodfish throughout the United States and has been introduced into multiple states. There does not seem to be any considerable impact on their population that would harm their population numbers drastically in the near future. There are certain ecological needs that the bigmouth have in order to live though. They prefer shallow, slow-moving water like flooded vegetation. Bigmouth buffalo are also susceptible to anchor parasites which can lead to secondary infections which can be harmful in poor water conditions. Future management plans may need to include a treatment of major bigmouth buffalo habitats for these parasites if they become more abundant. In some areas of its distribution bigmouth buffalo may present a problem with overpopulation, there have been studies done on the effectiveness of electrical barriers in Lake Heron to decrease the population. A way to maintain the current populations or decrease them will certainly be a potential management need in the future for certain areas if cases like Lake Heron become more common.
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 which flows through Alberta and the Qu'Appelle River which flows through Saskatchewan and Manitoba into Lake Winnipeg. Beginning in the northern United States they are native to Iowa, South Dakota and Minnesota, more southern states include eastern Texas and Oklahoma. The major drainages they are found in include Lake Erie, Ohio River, and Mississippi River drainages. From these drainages they are found into Arkansas, the Gulf region of Louisiana and down the Tennessee River into Alabama. The introduction of bigmouth has been largely done for commercial purposes. The regions include reservoirs within Arizona, North Dakota and Montana. The reservoirs in North Dakota and Montana are of the Missouri River drainage. Within California they have also been introduced to the aqueduct system of Los Angeles. And also Kansas  The distribution has only increased in size so there is nothing determined to extirpate the bigmouth.
The bigmouth buffalo has numerous ecological needs. Diet is important in any organisms' ecology. The larval bigmouth are benthic feeders of copepods and cladocerans mostly but also eat phytoplankton and chironomids. The juveniles and adults are benthic and limnetic plankton feeders that also eat cladocera, copepods, algae, Chironomidae, ostracods, and other insect larvae and invertebrates depending on availability. The optimum habitat for bigmouth buffalo requires highly vegetated and turbid waters. Turbidity levels of over 100 ppm are optimal, they also like muddy bottoms. A minimum total dissolved solids is 200 ppm during the growing season. During spring and summer there should be 50–75% pools, backwaters, and marsh areas and 25-75% littoral area and protected embayments during summer for the habitat to be suitable. Bigmouth can be found in waters from 22.5–38.0°C but their preferred temperature is between 31-34°C. The optimal temperature for incubation and hatching of eggs is from 15-18°C but they can develop in temperatures reaching up to 26.7°C. The bigmouth prefer slow-moving water that does not reach a velocity over 30 cm/s. Salinity can be a problem for reproduction. Spawning can occur from 1.4-2.0 ppt of salinity which eggs and yearlings not being able to survive a salinity of over 9 ppt. The minimum dissolved oxygen during the spring and summer is 5 mg/l. All of these factors in the ecology of bigmouth buffalo result in their seclusion to slow-moving vegetated/marshy areas in oxbows of rivers and reservoirs.
The bigmouth buffalo is a spring spawner generally spawning between April and June when the water temperature is between 13–26°C. The bigmouth is a broadcaster that has adhesive eggs which it lays in highly vegetated waters. They seek high submergent and emergent vegetation and high turbidity to keep their eggs safe and in ideal habitat for hatching. The substrate found is generally a mixture of a medium amount of rubble and gravel and a high amount of sand and silt. The water levels but substantially rise before spawning and stabilize afterwards. The sexual maturity of bigmouth is dependent on their size. Females mature once they are over 475 mm while males begin to mature around 305–328 mm and should be mature by the time they are 356–379 mm. The bigmouth are group spawners which produce 250,000 eggs/kg of adult weight, their eggs are approximately 1.5 mm in diameter. The age of bigmouth is around 2 years old when they reach sexual maturity but it is said that they have been found as old as 20.
The bigmouth buffalo is not listed as threatened or endangered in any region of its native or introduced distribution. There is a parasite that fingerlings are susceptible to, Lernea cyprinacae, but most are unaffected by the time they reach a length of 30 mm. They are anchor parasites that insert themselves between scale margins and fin insertions. The real problem is a secondary infection that may arise due to these parasites, the protozooan Epistylis and bacteria Flavobacterium columnare are both attached to serious parasite infestations. It has been reported that bigmouth hybridizes. The bigmouth has been seen to hybridize in the wild with smallmouth buffalo, and it is possible that some fish identified as black buffalo are indeed these hybrids. The hybridization does not seem to be negatively impacting their populations but makes it difficult to determine how many hybrids and how many black buffalo are actually in certain reservoirs and therefore difficult to manage for either species. There are currently no found specific management plans for the bigmouth buffalo either privately or governmentally funded. Bigmouth buffalo are seen as a commercial foodfish for the most part and do not seem to be in any danger of decreasing in population. They are very readily reproduced by hatcheries and if ever needed could be easily stocked.
Overall there is no need to protect or set aside conservation easements for the bigmouth buffalo, it seems to be a very well adapted species to its range and maintains its population well naturally. However it would be good to have a proper estimate on the abundance of species across its native range and monitored in order to catch any beginning of decline quickly to take action. Since the bigmouth is a foodfish it is easy to look at the commercial catching as a way to sample the population. It is shown that knotted nets can harm the fish causing hemorrhages and scale loss which would not be conducive to having little impact on the species while sampling. It would be ideal to seine for the bigmouth through oxbows and other regions of their range. This should be done in multiple locations in the Lake Erie, Ohio River, Mississippi River, Tennessee River, Milk River, Los Angeles aqueducts and Missouri River reservoirs where the fish are known to be caught. The species should be netted, sized, counted, and released. If the funding was available it would be good to tag the small ones for future population estimates. Doing this every five years or so would give a good dynamic population estimate.
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On June 21, 2013, Austin Morgan (16 years old) caught the Wisconsin state record bigmouth buffalo fish. It measured 49.5 inches and weighed 76.8 pounds. Amazingly, it was caught on an 5 lb. test line and Austin only weighed 60.5 pounds more than the fish. It was caught on the Wisconsin River at Devil's Elbow which is on the north end of the Petenwell Flowage. It was officially recognized to be the new world record by the National Fresh Water Fishing Hall of Fame as both 8 lb line class and all tackle. A Mt. Juliet, Tennessee, man is in the record books for catching a 62-pound (28 kg) bigmouth buffalo while fishing on Percy Priest Lake. The fish, caught by Jeff Wilkins in late March, was 45 inches (110 cm) in length and snagged in the Seven Points area of the lake. The Tennessee Wildlife Resources Agency said it took him 35 minutes to reel in the fish. The new record surpasses the previous mark of 52 pounds, two ounces, previously held since April 6, 2001 by Greg Megibben. The giant fish also came from Percy Priest Lake. After the record was certified, Wilkins released the fish back into the lake. In Omaha, Nebraska, Joe Slavic is in the record books for catching a 64-pound (29 kg) Buffalo Bigmouth on June 8, 2000, in a sand pit located in Dodge County.
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