''Hiodon tergisus'', the mooneye, is a freshwater fish that is widespread across eastern North America.

Anatomy and appearance

''H. tergisus'' is characterized by its silvery appearance, strongly compressed deep body, and

keel The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic and counterbalancing purpose, as well. As the laying down of the keel is the initial step in the construction of a ship, in Br ...

that extends from its anal to pelvic fin. Adult mooneyes reach an average length of R. Wallus and J. P. Buchanan. Contributions to the Reproductive Biology and Early Life Ecology of Mooneye in the Tennessee and Cumberland River. American Midland Naturalist. Vol. 122, No. 1 (Jul., 1989), pp. 204–207 and may reach up to . They weigh an average of .

Distribution

Mooneyes are endemic to eastern North America. They can be found as far north as the

Hudson Bay Hudson Bay ( crj, text=ᐐᓂᐯᒄ, translit=Wînipekw; crl, text=ᐐᓂᐹᒄ, translit=Wînipâkw; iu, text=ᑲᖏᖅᓱᐊᓗᒃ ᐃᓗᐊ, translit=Kangiqsualuk ilua or iu, text=ᑕᓯᐅᔭᕐᔪᐊᖅ, translit=Tasiujarjuaq; french: b ...

and as far south as the

Mississippi delta The Mississippi Delta, also known as the Yazoo–Mississippi Delta, or simply the Delta, is the distinctive northwest section of the U.S. state of Mississippi (and portions of Arkansas and Louisiana) that lies between the Mississippi and Yazoo ...

. They have been found as far west as central

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...

, Canada, and as far east as the western edge of

North Carolina North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia and So ...

. Historically, mooneyes have been found in all of the

Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lakes ...

, excluding

Lake Superior Lake Superior in central North America is the largest freshwater lake in the world by surface areaThe Caspian Sea is the largest lake, but is saline, not freshwater. and the third-largest by volume, holding 10% of the world's surface fresh wa ...

.Hammerson, G. 2012 Hiodon Tergisus. NatureServe Explorer: An online encyclopedia of life Their populations in

Lake Michigan Lake Michigan is one of the five Great Lakes of North America. It is the second-largest of the Great Lakes by volume () and the third-largest by surface area (), after Lake Superior and Lake Huron. To the east, its basin is conjoined with that o ...

and

Lake Erie Lake Erie ( "eerie") is the fourth largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has t ...

have been declining. Furthermore, their current distribution is becoming more confined to larger rivers, whereas historically they have inhabited much smaller

tributaries A tributary, or affluent, is a stream or river that flows into a larger stream or main stem (or parent) river or a lake. A tributary does not flow directly into a sea or ocean. Tributaries and the main stem river drain the surrounding drainage b ...

. The historical distribution of ''H. tergisus'' may not be fully accurate due to the misidentification with other species, such as

gizzard shad ''Dorosoma'' is a genus that contains five species of shads, within the herring family Clupeidae. The five species are native to the North and/or Central America, and are known from both fresh water and the waters of estuaries and bays. The Am ...

and . The difference between current and historical distributions may be due to the construction of dams that restrict fish from migrating from smaller rivers to large rivers. Factors such as climate change and pollution may also affect their distributions.

Ecology

Mooneyes inhabit clear river and lake environments. They are mostly intolerant of

turbid Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Fluids can ...

waters and are usually active during the day. As surface feeders, they eat primarily aquatic and terrestrial insects, but they are also known to eat

crustaceans Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

mollusks Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

, and small fish.D. Etnier and Wayne Starnes. The Fishes of Tennessee. The University of Tennessee press/Knoxville. p117-118. 1993 Young mooneyes tend to feed in more

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

regions, eating immature

caddisflies The caddisflies, or order Trichoptera, are a group of insects with aquatic larvae and terrestrial adults. There are approximately 14,500 described species, most of which can be divided into the suborders Integripalpia and Annulipalpia on the b ...

mayflies Mayflies (also known as shadflies or fishflies in Canada and the upper Midwestern United States, as Canadian soldiers in the American Great Lakes region, and as up-winged flies in the United Kingdom) are aquatic insects belonging to the order ...

midges A midge is any small fly, including species in several families of non-mosquito Nematoceran Diptera. Midges are found (seasonally or otherwise) on practically every land area outside permanently arid deserts and the frigid zones. Some midg ...

, corixids, and plecopterans. Although no predators of adult mooneyes are known, young mooneyes are susceptible to predation by larger

piscivorous A piscivore () is a carnivorous animal that eats primarily fish. The name ''piscivore'' is derived . Piscivore is equivalent to the Greek-derived word ichthyophage, both of which mean "fish eater". Fish were the diet of early tetrapod evoluti ...

fish. Two

trematode Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host ...

parasites specific to ''H. tergisus'' are '' Crepidostomum hiodontos'' and '' Paurorhynchus hiodontis''. Researchers believe these parasites are derived from ingested food items. Thus far, no research has been done on how or if these parasites affect populations and ecology of mooneyes. ''H. tergisus'' has latitudinal variation in growth rates in which northern populations mature faster than southern populations. This may be due to less turbidity in the northern latitudes.C. Katechis, P. Sakaris and E. R. Irwin. Population Demographics of Hiodon tergisus (Mooneye) in the Lower Tallapoosa River. Southeastern Naturalist , Vol. 6, No. 3 (2007), pp. 461–470

Lifecycle

Mooneyes are spring spawners. Since their distribution varies greatly in latitudinal gradient, southern populations spawn much sooner than northern populations, in March and April compared to June and July, respectively. Each spring, adult mooneyes migrate upstream to clearer waters to spawn. Females are capable of producing 10,000-20,000 semibuoyant eggs each year. They prefer clear-running water and solid substrates when spawning. Newly hatched

larvae A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

are in length and mostly inhabit the limnetic portion of the

water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...

. Mooneyes eat larval forms of mayflies, caddisflies, and midges during the first few months after hatching. Mooneyes exhibit rapid growth within their first year, reaching up to . Adult mooneyes reach an average length of . Females reach sexual maturity at four to five years and males reach sexual maturity at three, and will continue to spawn every year after. Males live up to seven years and females are capable of living up to nine years.

Conservation and management

Currently, ''H. tergisus'' is listed as threatened in

New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...

, and

Michigan Michigan () is a state in the Great Lakes region of the upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the 10th-largest state by population, the 11th-largest by area, and the ...

.Protected Wildlife Species of North Carolina N.C. Wildlife Resources Commission Nov. 2008Dean Bouton & Eileen C. Bouton and Stegemann Endangered and Threatened Fishes of New York. The Conservationist. Sept. 1993. Although mooneyes inhabit much of eastern North America, many of their habitats are isolated or discontinuous, so if an isolated population goes extinct or begins to go extinct, no influx of outside mooneyes can take their place. Furthermore, the development of agricultural and industrial practices has led to low water quality. ''H. tergisus'', along with other pollution-intolerant fish in the Ohio River, have migrated north away from polluted waters over the past 20 years. According to the

New York State Department of Environmental Conservation The New York State Department of Environmental Conservation (informally referred to as NYSDEC, DEC, EnCon or NYSENCON) is a department of New York state government. The department guides and regulates the conservation, improvement, and protection ...

, the decline in population may be due to increased

siltation Siltation, is water pollution caused by particulate terrestrial clastic material, with a particle size dominated by silt or clay. It refers both to the increased concentration of suspended sediments and to the increased accumulation (temporary or ...

or competition with newly

introduced species An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived there ...

. Dams are another factor affecting not only mooneye populations, but also a variety of other fish species. Dams are particularly bad due to their ability to block migration routes of mooneyes and other species. Currently, no direct management efforts for ''H. tergisus'' are active.

References

{{Taxonbar, from=Q931237 Hiodontidae Fish of North America Taxa named by Charles Alexandre Lesueur Fish described in 1818 Freshwater fish of North America