Compiling all species mentioned across various sources. Hudson & James Bay is mostly brackish, having an extremely high freshwater inflow from large rivers and a low evaporation rate due to its freezing temperatures. Most of the ichthyofauna of the basin are freshwater species that have adapted some salt tolerance, such as walleye, brook trout, burbot, and several whitefish species.

This list is of the comparatively few entirely marine species known from Hudson & James Bays. All are arctic in origin, as there's no means of fish dispersal other than through the arctic via the Hudson Strait.

Great article here by Mark Conboy on the fishes of the region.

https://publications.gc.ca/collections/collection_2007/dfo-mpo/Fs97-4-2674E.pdf