alligator-fish

from The Century Dictionary.

• noun An agonoid fish, Podothecus acipenserinus, with a compressed tapering body, about 12 polygonal plates on the breast, 9 spines and 7 rays in the dorsal fins, gill-membranes united to the isthmus, and the lower jaw shutting within the upper. It is about a foot in length, and is common from Puget Sound northward.
• noun Any agonid; a fish of the family Agonidæ (which see).