Twenty fish species have been found in the waters of NPR-A. Eleven are in the salmonid family. Of these, seven are anadromous, meaning that they spawn in fresh water but spend some portion of their life cycle in the ocean. This strategy results in some waters of NPR-A being used for part of the year, even though they may be frozen solid at other times. These species are the arctic cisco, broad whitefish, humpback whitefish, least cisco, pink salmon, chum salmon and chinook salmon. None of the salmon species is very numerous this far north.
Most ichthyologists currently consider the char to be two species.
One, still called the arctic char, is a year-round resident of deep lakes. The other, dolly varden, lives in rivers, but some individuals are anadromous. Other species found in NPR-A are rainbow smelt, ninespine stickleback, slimy sculpin, fourhorn sculpin, Alaska blackfish, northern pike, longnose sucker, burbot and arctic flounder.