An adult male 160 cm long weighed about 47 kg. In at least some populations the color of the back extends to a circle around the eye, onto the pectoral fin, and to the sides of the tail. In some populations the sides are yellowish orange and there is a bright yellow patch on each side of the dorsal fin near the top. The underparts of S. f. guianensis are white, pinkish, or grayish. In S. f. fluviatilis the upper parts are bluish or pearl gray, the color being darker anteriorly.
Larger animals are noticeably paler above.
The pectoral fin, both above and below, is the same color as the back. The underparts are pinkish white to white. A prominent band of the ventral coloration extends upward on the sides of the body to slightly above the level of the eye. The dorsal color, however, extends down to a distinct line from the corner of the mouth to the base of the pectoral fin and includes the eye. The tip of the beak and the apex of the dorsal fin are conspicuously white.