Moonfish is a fish. The very deep, thin, sharp-edged body of the moonfish (adults are scarcely twice as long as deep, and young fry even deeper, relatively), tapering to a slender caudal peduncle, and the concave upper anterior profile of its head, are enough to separate it at a glance from pilotfish, scad, crevalle, hardtail, saurel, or goggle eye; its very low dorsal and anal fins distinguish it from the lookdown, which is of something the same shape (cf. fig. 204 with fig. 205). Its minute ventral fins, soft dorsal fin and anal fin which are nearly even in height from end to end, separate it from the threadfin, and from the Cuban jack (Hynnis cubensis), now thought to be the adult of the threadfin.