Yes, WEAKFISH is a Scrabble word!

Letter values in Scrabble US: W 4, E 1, A 1, K 5, F 4, I 1, S 1, H 4.

Is it a valid word?

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

lean flesh of food and game fishes of the Atlantic coast of the United States
food and game fish of North American coastal waters with a mouth from which hooks easily tear out

Also: cynoscion regalis.