Cuvier & Valenciennes, 1846
Eohiodon Cavender, 1966
The mooneyes are a family, the Hiodontidae, of primitive ray-finned fish comprising two living and three extinct species in the genus Hiodon. They are large-eyed, fork-tailed fish that physically resemble shads. Their common name comes from the metallic gold or silver shine of their eyes.
The higher classification of the mooneyes is not as yet fully established. Some sources place them in their own Order - Hiodontiformes (as in the treatment here), while others retain them in the order Osteoglossiformes.
The fish monitoring plan described below was developed for Hiodon tergisus (Mooneyes), which are important native freshwater fish to North America. Tergisus is characterized by its silvery appearance, strongly compressed deep body, and keel that extends from its anal to pelvic fin (Hammerson). Hiodon contains only two species, tergisus and alosiodes, both of which are classified in the subgroup Osterglossimorpha. They are the only two species in this subgroup in North America. The average length for H. tergisus is 28 cm, but they are capable of reaching lengths up to 45 cm (MSUBT). H. tergisus can be found throughout Eastern North America, stretching from the Hudson Bay region all the way to the Mississippi River delta. Their natural habitat includes medium to large rivers and deep lakes with low turbidity. Although they are invertivores, they have been known to eat other fish. H. tergisus has no known natural predators as adults, but they are at risk of predation during early stages of life by picivorous fish. Spawning in the spring, Tergisus migrates to local spawning areas where it releases “semibouyant” eggs (Hammerson). This species has a life span of 7 to 9 years, with the females generally living the longest. Currently, H. tergisus is not endangered or threatened; however, it is susceptible to decline. Although its distribution is large, many populations are isolated from one another due to human influence. This isolation, along with urbanization that increases turbidity, could eventually negatively affect this species (MSUBT). Conservation efforts must be taken to allow alternate pathways for separate populations to connect and lower human pollution through waste management and other practices.
Mooneyes are endemic to eastern North America. They can be found as far north as the Hudson Bay and as far south as the Mississippi delta. They have been found as far west as central Alberta, Canada, and as far east as the western edge of North Carolina. Historically Mooneyes have been found in all of the Great Lakes, excluding Lake Superior (Hammerson). Currently, their populations in Lake Michigan and Lake Erie have been declining. Furthermore, the current distribution of Mooneyes is becoming more confined to larger rivers, whereas historically they have inhabited much smaller tributaries. The historical distribution of Hiodon tergisus may not be fully accurate due to the misidentification with other species, such as gizzard shad and alewifes (MSUBT). 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.
Mooneyes inhabit non-turbid river and lacustrine environments. They are mostly intolerant of turbid waters and are usually active during the day. As surface feeders, Mooneyes eat primarily aquatic and terrestrial insects, but they are also known to eat crustaceans, mollusks, and small fish (D. Etnier and Wayne Starnes). Young mooneyes tend to feed in more benthic regions, eating immature caddisflies, mayflies, midges, corixids, and plecopterans. Although there are no known predators of adult mooneyes, young mooneyes are susceptible to predation by larger piscivorous fish (Boltz). Two metazoan parasites specific to Hiodon tergisus are Crepidostomum hiodontos and Paurorhynchus hiodontis. Researchers believe said 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 (Glenn). Studies have shown that Hiodon tergisus observe 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 (Katechis).
Mooneyes are spring spawners. Since their distribution varies greatly in latitudinal gradient, southern populations spawn much sooner than northern populations. The southern populations spawn in March and April, and the northern populations spawn in June and July. Each spring, adult mooneyes migrate upstream to clearer waters to spawn. Females are capable of producing 10,000-20,000 semi buoyant eggs each year (D. Etnier and Wayne Starnes). Mooneyes prefer clear running water and solid substrates when spawning. Newly hatched larvae are 8–9 mm in length and mostly inhabit the limnetic portion of the water column. Mooneyes eat larval forms of mayflies, caddisflies and midges during the first few months after hatching (MSUBT). Mooneyes exhibit rapid growth within their first year, reaching up to 200mm. Females reach sexual maturity at 4–5 years and males reach sexual maturity at 3 and will continue to spawn every year after. Adult mooneyes reach an average length of 298 mm and weigh an average of 226 grams (R. Wallus and J. P. Buchanan). Males live up to 7 years and females are capable of living up to 9 years (Glenn and Williams).
Currently Hiodon tergisus is listed as threatened in the states of New York, North Carolina, and Michigan (Protected Wildlife Species of North Carolina; Bouton and Stegemann; MSUBT). Although mooneyes inhabit much of eastern North America, many of their habitats are isolated or “discontinuous.” This means that if an isolated population goes extinct or begins to go extinct there will not be an influx of outside mooneye to take their place. Furthermore, the development of agricultural and industrial practices has led to low water quality (MSUBT). In a study by the University of Louisville, researchers found that Hiodon 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 New York’s Department of Environmental Conservation the decline in Mooneye population may be due to increased siltation or competition with newly introduced species (Bouton and Stegemann). 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 routs of mooneyes and other species (Katechis). Currently there are no direct management efforts for Hiodon tergisus. One of the main reasons why no management practices are yet in place is because very little research has been done on this species. Furthermore, more threatened species such as the lake sturgeon are taking priority in conservation efforts.
Since little research has been done on the current standing of Hiodon tergisus, studies need to be done on the size of the mooneye population and where individuals are located. This can be accomplished by performing and comparing random transect sampling across known successful habitats and across habitats that are suspected of struggling. Gill nets can be placed in lacustrine habitats and seines may be used for river habitats to collect samples. Also, research must be done on potential causes of the decline in population. Each population may have a different cause for their decline. Check for turbidity using a turbidity meter, or if it is a stream, look to see if it ends at a dam downstream. Since little research has been done on how parasites affect mooneye populations, inspect fish for Crepidostomum hiodontos and Paurorhynchus hiodontis. Also, look for invasive species that eat the same food as mooneyes. Depending on the cause and its severity, certain measures must be taken. If a dam is blocking the mooneyes’ migratory path, an alternate path must be made through or around the dam. In a situation were turbidity resulting from agriculture or urbanization has significantly impacted the population, new polices must be made restricting the dumping or runoff of pollutants. Furthermore, policies must be made to encourage fishermen to catch and release of mooneyes in vulnerable areas, such as New York or Lake Michigan. In North Carolina, where mooneyes are almost extinct, fish hatcheries can reestablish a population if managed correctly. In the long run, Hiodon tergisus populations need to be monitored annually in order to track success and management.
The goldeye (Hiodon alosoides (Rafinesque, 1819)) is also widespread across North America, and is notable for a conspicuous golden iris in the eyes. It prefers turbid slower-moving waters of lakes and rivers, where it feeds on insects, crustaceans, fish, frogs, shrews, and mice. The fish has been reported up to 52 centimetres (20 in) in length. The smoked meat is highly valued and sold as "Winnipeg goldeye".
- Hilton, E. J. & Grande, L. 2008; "Fossil Mooneyes (Teleostei: Hiodontiformes, Hiodontidae) from the Eocene of western North America, with a reassessment of their taxonomy" in "Birth of the modern world: the Tertiary" Geological Society, London, Special Publications 295:221-251
- Berra, Tim M. (2001). Freshwater Fish Distribution. San Diego: Academic Press. ISBN 0-12-093156-7
- Froese, Rainer, and Daniel Pauly, eds. (2011). "Hiodontidae" in FishBase. June 2011 version.
- L. Guo-Qing and M. V. H. Wilson. An Eocene Species of Hiodon from Montana, Its Phylogenetic Relationships, and the Evolution of the Postcranial Skeleton in the Hiodontidae (Teleostei). Journal of Vertebrate Paleontology Vol. 14, No. 2 (Jun. 22, 1994), pp. 153–167
- E. S. Zyznar, F. B. Cross and J. A. C. Nicol. Uric Acid in the Tapetum Lucidum of Mooneyes Hiodon (Hiodontidae Teleostei). Proceedings of the Royal Society of London. Series B, Biological Sciences , Vol. 201, No. 1142 (Apr. 13, 1978), pp. 1–6.
- 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
- 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
- C. Glenn. Seasonal Parasitic Infections In Mooneye, Hiodon-tergisus (Lesueur). The Assinboine River Canadian Journal Of Zoology-Revue Canadienne De Zoologie Vol: 58 Issue: 2 Pages: 252-257 Published: 1980
- 2004. Hiodon Tergisus. Michigan State University Board of Trustees.
- Hammerson, G. 2012 Hiodon Tergisus. NatureServe Explorer: An online encyclopedia of life
- Dean Bouton & Eileen C. Bouton and Stegemann Endangered and Threatened Fishes of New York. The Conservationist. Sept. 1993.
- Protected Wildlife Species of North Carolina N.C. Wildlife Resources Commission Nov. 2008
- W. and B. Pearson. Fishes of the Ohio River. Ohio Journal of Science Vol. 89 Issue 5 p. 181-187. 1989.
- D. Etnier and Wayne Starnes. The Fishes of Tennessee. The University of Tennessee press/Knoxville. p117-118. 1993
- Jay R. Stauffer, Jr., Jeffrey M. Boltz and Laura R. White. The Fishes of West Virginia. Proceedings of the Academy of Natural Sciences of Philadelphia , Vol. 146, (1995), pp. 1–389