Yes, MONKFISHES is a Scrabble word!

Letter values in Scrabble US: M 3, O 1, N 1, K 5, F 4, I 1, S 1, H 4, E 1, S 1.

Is it a valid word?

MONKFISHES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

flesh of a large-headed anglerfish of the Atlantic waters of North America
fishes having large mouths with a wormlike filament attached for luring prey
sharks with broad flat bodies and winglike pectoral fins but that swim the way sharks do

Also: angler fish, lophius americanus, angel shark, squatina squatina.

Not playable in Scrabble US: ALLMOUTH.