The Arctic grayling (Thymallus arcticus) is a species of freshwater fish in the salmon family Salmonidae.

[9] The Arctic grayling occurs primarily in cold waters of mid-sized to large rivers and lakes, returning to rocky streams to breed.

Adult fish seek shallow areas of rivers with fine, sand substrate and moderate current.

Although the Arctic grayling does not excavate a nest, the highly energetic courtship and mating tends to kick up fine material which covers the zygotes.

The fluvial population in the upper Missouri river basin once merited a high priority for listing under the Endangered Species Act (ESA) by the US Fish & Wildlife Service (FWS).

This unique southernmost population is now extirpated from all areas of the basin with the exception of the Big Hole River watershed.

In preparation for an ESA listing, the US FWS began implementing a "Candidate Conservation Agreement with Assurances" (CCAA).

This agreement protects cooperating landowners from being prosecuted under the ESA "takings" clause so long as they fulfill specific obligations, spelled out in a contractual arrangement and intended to restore the dwindling population.