Body riband shaped; dorsal fin as long as the body; anal absent; caudal rudimentary, or not in the longitudinal axis of the fish.
Fig. 237.—Trachypterus tænia.
The “Ribbon-fishes” are true deep-sea fishes, met with in all parts of the oceans, generally found when floating dead on the surface, or thrown ashore by the waves. Their body is like a band, specimens of from fifteen to twenty feet long being from ten to twelve inches deep, and about an inch or two broad at their thickest part. The eye is large and lateral; the mouth small, armed with very feeble teeth; the head deep and short. A high dorsal fin runs along the whole length of the back, and is supported by extremely numerous rays; its foremost portion, on the head, is detached from the rest of the fin, and composed of very elongate flexible spines. The anal fin is absent. The caudal fin (if preserved, which is rarely the case, in adult specimens) has an extra-axial position, being directed upwards like a fan. The ventrals are thoracic, either composed of several rays or reduced to a single long filament. The coloration is generally silvery, with rosy fins.
When these fishes reach the surface of the water the expansion of the gases within their body has so loosened all parts of their muscular and bony system, that they can be lifted out of the water with difficulty only, and nearly always portions of the body and fins are broken and lost. The bones contain very little bony matter, are very porous, thin and light. At what depths Ribbon-fishes live is not known; probably the depths vary for different species; but although none have been yet obtained by means of the deep-sea dredge, they must be abundant at the bottom of all oceans, as dead fishes or fragments of them are frequently obtained. Some writers have supposed from the great length and narrow shape of these fishes that they have been mistaken for “Sea-serpents;” but as these monsters of the sea are always represented by those who have had the good fortune of meeting with them as remarkably active, it is not likely that harmless Ribbon-fishes, which are either dying or dead, have been the objects described as “Sea-serpents.”
Fig. 238.—Young Trachypterus.
Young Ribbon-fishes (from two to four inches) are not rarely met with near the surface; they possess the most extraordinary development of fin rays observed in the whole class of fishes, some of them being several times longer than the body, and provided with lappet-like dilatations. There is no doubt that fishes with such delicate appendages are bred and live in depths where the water is absolutely quiet, as a sojourn in the disturbed water of the surface would deprive them at once of organs which must be of some utility for their preservation.
Ribbon-fishes are divided into three genera:—
Trachypterus.—In which the ventral rays are well developed, and composed of several more or less branched rays. Specimens of this genus have been taken in the Mediterranean, Atlantic, at Mauritius, and in the Eastern Pacific. The “Deal-fish” (T. arcticus) is often met with in the North Atlantic, and specimens are generally found after the equinoctial gales on the coasts of the Orkneys and North Britain.