black·fish 
(blăkfĭsh′)
(blăkfĭsh′)n. pl. blackfish or black·fish·es
1. Any of various dark-colored fishes, such as:
a. A small edible freshwater fish (Dallia pectoralis) that inhabits streams and ponds of Alaska and Siberia and is noted for its ability to withstand freezing.
b. See tautog.
2. Any of several dark-colored toothed whales, especially the pilot whale.