Table of Contents
The filefishes recall the triggerfishes in their general form, being similarly deep and flattened sidewise, with the same peculiar profiles, small terminal mouths, projecting incisor teeth, eyes set high up, very stout dorsal spines, and short gill openings; also in the fact that the ventral fins are either lacking altogether or at least are reduced to a single short blunt movable spine at the end of the very long pelvic bone, forming a keel-like continuation of the general ventral profile of the head and connected with that of the belly by a dewlap of skin. The filefishes differ from triggerfishes in having only one dorsal spine instead of three, and in the fact that their scales are so minute that the skin is velvety to the touch although very tough. Most of the species are tropical or subtropical, and none has any commercial or sporting value. Adults of the four species known from the Gulf of Maine are separable as follows:
| KEY TO GULF OF MAINE FILEFISHES | |||
|---|---|---|---|
| 1. | There is a prominent external ventral spine; the gill openings are nearly vertical | 2 | |
| There is no external ventral spine; the gill openings are very oblique | 3 | ||
| 2. | Dorsal profile of head in front of the eyes is straight, or only very slightly concave; there are no thorns on the sides of the caudal peduncle | — | Filefish (Monacanthus hispidus), p. 522 |
| Dorsal profile of head in front of the eyes is conspicuously concave; there are about 6 stout thorns pointing forward on each side of the caudal peduncle | — | Filefish (Monacanthus ciliatus), p. 523 | |
| 3. | Dorsal fin with about 34 to 38 soft rays; anal with 36 to 41 rays; also, in small specimens, the caudal fin is more than one-half as long as the body | — | Orange filefish (Alutera schoepfii), p. 524 |
| Dorsal fin with about 44 to 48 soft rays; anal with 47 to 52 rays; also, in small specimens, the caudal fin is less than one-half as long as the body | — | Unicornfish, p. 525 (Alutera scripta) | |