Burbot

The burbot ("Lota lota") is the only gadiform (cod-like) freshwater fish. It is also known as bubbot, mariah, freshwater cod, freshwater ling, freshwater cusk, the lawyer, coney-fish, lingcod, and eelpout.
The burbot can live under ice, and it needs frigid temperatures to breed. "These were ice-age fish that once swam unhindered in a glacial world".