The southern kingcroaker can grow to about but a more usual adult length is . The southern kingcroaker is a slender fish, deepest about two fifths of the way along. The upper jaw projects further than the lower and the snout overhangs the mouth. There is a small
barbel on the fleshy lower lip. The dorsal fin is divided into two parts. The number of spines and soft rays in the fins is indicative of the species and in
M. americanus, the front part of the dorsal fin is broadly triangular and has 10 spines and the other part is long and has 1 spine and 22 to 25 soft rays. The pointed pectoral fins are large and the anal fin has 1 spine and 7 or 8 soft rays. The tail fin has a characteristic slightly concave upper lobe and a rounded lower lobe. The colour of the fish is silvery grey, sometimes with a coppery sheen, and paler grey below. There are sometimes several broad slanting bands of darker colour on the back of the fish. ==Distribution and habitat==