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

H. tergisus is characterized by its silvery appearance, strongly compressed deep body, and keel that extends from its anal to pelvic fin.

They have been found as far west as central Alberta, Canada, and as far east as the western edge of North Carolina.

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

[6] Young mooneyes tend to feed in more benthic regions, eating immature caddisflies, mayflies, midges, corixids, and plecopterans.

Newly hatched larvae are 8–9 millimeters (0.31–0.35 in) in length and mostly inhabit the limnetic portion of the water column.

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 decline in population may be due to increased siltation or competition with newly introduced species.