What's the noun for muttons? Here's the word you're looking for.
muttonfish
(chiefly US) Any of several Atlantic and Caribbean fishes which are said to taste of mutton, especially the mutton snapper, Lutjanus analis, the ocean pout, Macrozoarces americanus, or the Irish pompano, Diapterus auratus. [from 18th c.]
(Australia) Any of several edible molluscs of the genus Haliotis; an abalone. [from 19th c.]