The specific gravity of the flying-fish can be most admirably regulated in correspondence with the element through which it may move. The swim-bladder, when distended, occupies nearly the entire cavity of the abdomen, thus containing a large volume of air; and in addition to this, there is a membrane in the mouth which can be inflated through the gills. The pectoral fins, though so large when expanded, can be folded into an exceedingly slender, neat, and compact form, so as to be no hindrance to swimming. A light displayed from the chains of a vessel in a dark night, will bring many flying-fishes on board, where they are esteemed as a great delicacy. Their fate, thus to be persecuted in both elements and to find security nowhere, has often been pitied in prose and verse; but although they excite so much sentimental commiseration, they are themselves no less predaceous than their enemies, feeding chiefly on smaller fishes.
The flying-fish of the West Indian waters is frequently allured by the tepid waters of the Gulf-stream into higher latitudes, and Pennant cites several examples of its having been found near the British coast.
The Flying-Gurnard (_Trigla volitans_) of the Mediterranean, Atlantic, and Indian seas, a highly singular and beautiful species, also raises itself into the air by means of its large pectoral fins. It does not fly very high, but swings itself as far as a musket-ball reaches, and may thus elude even the rapidity of the dolphin. That strangely formed fish, the _Pegasus_ of the Indian seas, is also enabled by its large pectoral fins to support itself for some moments in the air, when it springs over the surface of the water.
Neither the quadrupeds nor the birds are subject to so many persecutions as the fishes, which have inexorable enemies in all classes of animals. Numberless molluscs and zoophytes feed upon their eggs, or devour their minute fry; myriads of sea-birds are on the look-out for them along the strands, or on the high ocean; seals and ice-bears lie in wait for them, while with weapons and deceit, with net, angle and harpoon, man carries death and destruction into their ranks. It would be a difficult task to state with any degree of exactness the number of fishermen disseminated over the face of the globe, but if we consider that, on a moderate calculation, at least a million of persons are directly or indirectly engaged in fishing in Great Britain and Ireland alone, and then cast a glance over the immense coast-line of the ocean, we may without exaggeration affirm that at least one-fiftieth part of the human race lives upon the produce of the seas. If we further reflect that fishes form a great part of the food of all coast-inhabitants, and consider in what masses they are sent into the interior,--fresh, dried, salted, smoked, and pickled,--we cannot doubt that the great extent of the ocean only apparently limits the numbers of the human race, for how many thousands of square miles of the most fruitful soil would it not require to bring forth the quantity of food which the blue and green fields of ocean supply to man? "Bounteous mother," "_Alma parens_," was the name given by the grateful ancients to the corn and grass-producing, herd-feeding earth; but how much more deserving of that endearing appellation is the sea, that, without being ploughed or manured, dispenses her gifts with such inexhaustible profusion! Numberless indeed are the various kinds of fishes which she furnishes to man, for almost every species affords an equally agreeable and healthy food: but of all the finny families or tribes that people the ocean none can compare for utility with that of the _Clupeidæ_, or Herrings, small in size but great in importance. In mile-long shoals, often so thickly pressed that a spear cast into them would stand upright in the living stream, the common herring appears annually on the coasts of north-western Europe, pouring out the horn of abundance into all the lochs, bays, coves, and fiords, from Norway to Ireland, and from Orcadia to Normandy. Sea-birds without end keep thinning their ranks during the whole summer; armies of rorquals, dolphins, seals, shell-fish, cods, and sharks devour them by millions, and yet so countless are their numbers, that whole nations live upon their spoils.