Yes, CRAYFISH is a Scrabble word!

Letter values in Scrabble US: C 3, R 1, A 1, Y 4, F 4, I 1, S 1, H 4.

Is it a valid word?

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

warm-water lobsters without claws; those from Australia and South Africa usually marketed as frozen tails; caught also in Florida and California
tiny lobster-like crustaceans usually boiled briefly
small freshwater decapod crustacean that resembles a lobster
large edible marine crustacean having a spiny carapace but lacking the large pincers of true lobsters

Also: spiny lobster, rock lobster, sea crawfish.

Not playable in Scrabble US: ECREVISSE.