What is any marine fish of the genus Macrurus, in which the body and tail taper to a point; they mostly inhabit the deep sea; -- called also onion fish, and rat-tail fish called?

grenadier — (Zoöl.) Any marine fish of the genus Macrurus, in which the body and tail taper to a point; they mostly inhabit the deep sea; -- called also onion fish, and rat-tail fish. (Webster's 1913.)