Mooneye (Hiodon tergisus) is a freshwater species recorded in the United States.
Scientific name: Hiodon tergisus · Water: Freshwater
Size: up to 47 cm
The mooneye is a hiodontid whose adults occur in deep pools and backwaters of medium to large rivers, lakes and impoundments. Maximum length is about 47 cm total length, commonly about 28.3 cm, and it can live ten years. It is a gamefish. Fishing vulnerability is moderate at 38 of 100 and resilience medium. IUCN lists it as least concern.
It is endemic to eastern North America, reaching as far north as Hudson Bay and as far south as the Mississippi Delta, as far west as central Alberta and as far east as the western edge of North Carolina. Historically it occurred in all of the Great Lakes except Lake Superior, but its populations in Lake Michigan and Lake Erie have been declining, and its present distribution is becoming confined to larger rivers where it once used much smaller tributaries. Part of the apparent change may be inaccurate record-keeping, because the mooneye is easily mistaken for gizzard shad and alewives; the rest is put down to the dams that block fish from moving from smaller rivers into large ones, with climate change and pollution also implicated. It inhabits clear river and lake environments, is mostly intolerant of turbid water and is usually active by day. A surface feeder, it takes aquatic and terrestrial insects as well as crustaceans, molluscs and small fish, while the young feed in more benthic areas on immature caddisflies, mayflies, midges, corixids and stoneflies. No predator of adult mooneyes is known, but the young are vulnerable to larger piscivorous fish. Two trematode parasites are specific to the species, Crepidostomum hiodontos and Paurorhynchus hiodontis, and both are thought to be acquired from ingested food; whether they affect the fish's populations or ecology has not been studied. Growth rates vary with latitude, northern populations maturing faster than southern ones.
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