The round whitefish (Prosopium cylindraceum) is a freshwater species of fish that is found in North American drainages from Alaska to New England, including the Great Lakes except for Lake Erie,[2] and in Arctic tributaries of northeast Asia, as well as northern Kamchatka Peninsula and the northern coasts of the Sea of Okhotsk.

The round whitefish is now protected in some U.S. states, such as New York and New Hampshire, from harvest or possession as an endangered or threatened species.

Its back has a green tinge to its appearance with scales that range from sepia brown to bronze and are edged with black.

Fertilized eggs are 3.1–3.25 mm (0.12–0.13 in) in diameter and are held in spaces between rocks as well as in the ice crystals of the slushy, tributary floor.

[10] Round-fish are fall spawners, laying their eggs between early October and late November, when the water temperature is at or below 2.5 °C (36.5 °F).

[10] Round whitefish are found in cold freshwaters of Arctic seas, post-glacial lakes, rivers, and brackish waters.

[8][13] In addition to the previous list, the generalized feeding pattern of the round-fish diet includes amphipods, gastropods, isopods, chironomid larvae and pupae, and various aquatic insects, such as spiny water flea (Bythotrephes longimarus).

[10][13] Round whitefish are stable generalized feeders due to the majority of their food being found in the deeper parts of the water.

[14][13] When species return to their non-spawning body of water after spawning and winter, round-fish diet consists of more of chironomids, isopods, and gastropods.

During the migration to spawning sites, they mostly feed on spiny water fleas, black fly larvae, and other aquatic insects.

Although, this change in round-fish populations is minimal in comparison to other aquatic species,[citation needed] this could grow into a larger problem if global warming continues to progress.

[16] Predation from native and introduced species such as yellow perch (Perca flavescens), smallmouth bass (Micropterus dolomieu)[15][16] and rainbow smelt (Osmerus mordax)[15][17] are detrimental to existing populations and may prevent reintroductions of round whitefish.

[15][16] Siltation, which can damage spawning habitat, and chloride pollution from road salt runoff may also impact round whitefish in developed areas.