Zoarces viviparus has a continuous dorsal, caudal and anal fin with a characteristic notch at the caudal end of the dorsal fin, where the fin rays are short and spiny. The scales are minute and the skin is very slimy. It has a terminal mouth, with gill openings extending below the base of the well developed pectoral fins. Pelvic fins are present, but small. The body is coloured grey-brown on its dorsal surface, with several blotches, and is yellowish along its ventral side. Adults can occassionally reach 52 cm but are typically 25-35 cm long.