FILE-FISH

file-fish, or trigger-fish, the names given to fishes of the genus _balistes_ (and _monacanthus_) inhabiting all tropical and subtropical seas. their body is compressed and not covered with ordinary scales, but with small juxtaposed scutes. their other principal characteristics consist in the structure of their first dorsal fin (which consists of three spines) and in their peculiar dentition. the first of the three dorsal spines is very strong, roughened in front like a file, and hollowed out behind to receive the second much smaller spine, which, besides, has a projection in front, at its base, fitting into a notch of the first. thus these two spines can only be raised or depressed simultaneously, in such a manner that the first cannot be forced down unless the second has been previously depressed. the latter has been compared to a trigger, hence the name of trigger-fish. also the generic name _balistes_ and the italian name of "pesce balistra" refer to this structure. both jaws are armed with eight strong incisor-like and sometimes pointed teeth, by which these fishes are enabled, not only to break off pieces of madrepores and other corals on which they feed, but also to chisel a hole into the hard shells of mollusca, in order to extract the soft parts. in this way they destroy an immense number of molluscs, and become most injurious to the pearl-fisheries. the gradual failure of those fisheries in ceylon has been ascribed to this cause, although evidently other agencies must have been at work at the same time. the _monacanthi_ are distinguished from the _balistes_ in having only one dorsal spine and a velvety covering of the skin. some 30 different species are known of _balistes_ and about 50 of _monacanthus_. two species (_b. maculatus_ and _capriscus_), common in the atlantic, sometimes wander to the british coasts. [illustration: _balistes vidua_]