Body blue above, silvery below; variations in markings (spots, curved lines) occur. Silvery-yellow iris. When frightened or asleep, entire fish becomes mottled with very light and dark browns, with dark ones predominating in 7 diagonal zones across the sides; fins become mottled. Spines slender, pungent, venomous. Preopercle angle 85°-95°. Fine scales on cheek. Midline of thorax without scales. Superficially resembles S. canaliculatus and S. fuscescens, particularly when young, but differs by having a much more deeply forked tail (Ref. 1602).