Yes, SILVERSIDES is a Scrabble word!

Letter values in Scrabble US: S 1, I 1, L 1, V 4, E 1, R 1, S 1, I 1, D 2, E 1, S 1.

Is it a valid word?

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

small fishes having a silver stripe along each side; abundant along the Atlantic coast of the United States
the common North American shiner
small fishes having a silver stripe along each side; abundant along the Atlantic coast of the United States

Also: common shiner, notropis cornutus.