Synonyms for Blackfish (same or very similar meaning)
WordNet sense 1 (large dark-colored food fish of the Atlantic coast of North America):
tautog, Tautoga onitisWordNet sense 2 (small dark-colored whale of the Atlantic coast of the United States; the largest male acts as pilot or leader for the school):
pilot whale, black whale, common blackfish, Globicephala melaenaFrom the ODE community, based on WordNetadd/edit