Stretched like a promontory, sleeps or swims,
And seems a moving land, and at his gills
Draws in, and at his trunk spouts out, a sea.”
Their tails therefore are different from those of all other fish: they are placed so as to lie flat upon the surface of the water; while the other kinds have their tails, as we frequently see, upright or edge-ways. This position of the tail enables them to force themselves suddenly to the surface of the water, at pleasure. How well is it that animals of this enormous size do not approach our shores, for their presence would fright the other valuable fish from our coasts: they are therefore kept in the abysses of the ocean: just as wild beasts, impelled by the same over-ruling Power, which hide themselves in the recesses of the forest.[142]
The cartilaginous tribe, which have gristles instead of bones, unite the principal of both the other classes in their conformation: like the cetaceous, they have organs of hearing, and lungs: like the spinous, they have gills, and a heart without a partition. From the structure of their gills, these animals are enabled to live a longer time out of water than other fishes. The cartilaginous Shark, or Ray, lives some hours after it is taken; while the spinous Herring, or Mackarel, expires a few minutes after it is brought on shore. Some of this class bring forth their young alive; and others produce them by eggs, which are afterwards brought to maturity. Most fishes having cold blood, have not heat sufficient to produce the fœtus. The all-wise Creator therefore has ordained, that many of them shall propagate their species by eggs, and this they do near the shore; where, by means of the solar rays, the water is warmer, and fitter for that purpose; and also because water-insects abound more there, which afford the young fry nourishment. To the fish of the ocean, which cannot reach the shores by reason of the distance, the Creator has given eggs that swim, and these are hatched amidst the floating fucus, called sargazo. In all, however, the manner of gestation is nearly the same: for, on dissection, it is ever found, that the young, while in the body, continue in the egg till a very little time before they are brought forth; and as soon as they leave the shell, they also begin to quit the womb. It is confidently asserted, that the young of the several species of the Shark, when pursued, will take refuge in the belly of its mother, by swimming in at her mouth. Of the same class of fishes are the Ray, the Torpedo,[143] the Lamprey, the Sturgeon, the Diodon, the Angler, the Lump-Sucker, the Pipe Fish, the Hippocampus, or Sea Horse, the Sea Porcupine, and the Galley Fish.
Of the spinous, or bony kind of fishes, these are obviously distinguished from the rest, by having a complete bony covering to their gills; by their being furnished with no other method of breathing than through the gills only; by their bones which are sharp and thorny; and by their tails, which are placed in a situation perpendicular to the body. The history of any one of this order very much resembles that of all the rest. They propagate not by bringing forth their young alive, as do the cetaceous tribes, nor by distinct eggs, as do the generality of the cartilaginous tribes, but by spawn, or pease, as they are generally called, which they produce by hundreds of thousands. The bones of this order of fishes, when examined slightly, appear to be entirely solid; yet, when viewed more closely, every bone is seen to be hollow, and filled with a substance less rancid and oily than marrow. These bones are very numerous, and pointed; and, as in quadrupeds, are the props or stays to which the muscles are fixed, which move the different parts of the body. The number of bones in all spinous fishes of the same kind is always the same. As this species partake less of the quadruped in their formation than any other, so they can bear to live out of their own element a shorter time. Some, indeed, are more vivacious in air than others: the eel will live several hours out of water; and the carp has been known to be fattened in a damp cellar. The method is, by placing the fish in a net well wrapped up in wet moss, the mouth only out, and hung up in a vault; then fed with white bread and milk, and the net sometimes plunged into the water.
The spinous class of fishes is more prolific than any other animal. Although their usual way of propagation is by spawn, yet there are some, such as the eel and the blenney, which produce their young alive. Their power of increasing is such, that if they were suffered to multiply unmolested, and remain undiminished for only a few years, the progeny of an individual would far exceed all human calculation. It is asserted, that a single herring, in the space of twenty years, would yield an offspring greater in bulk than ten such globes as this we inhabit. A female herring deposits at least 10,000 eggs, in the sea near to Great Britain![144] A tench lays 1,000 eggs. There have been 200,000 ova or eggs found in a carp; and in one of eighteen inches, 342,144: in a perch, weighing one pound two ounces, 69,216; and in a sturgeon of one hundred and sixty pounds, there was the enormous number of 1,467,500. Leewenhoeck counted in a middling-sized cod, nine million 384,000.
This multiplication of fishes is very astonishing; but the fact is, as they are obliged to devour one another for necessary subsistence, the whole natives of the deep without these extraordinary supplies, would soon be totally extinct. Were they to bring forth no more at a birth than land animals, the increase would be far too small for the consumption. The weaker species would soon be destroyed by the stronger, and the latter would soon after perish. Therefore to supply millions of animals with food, and yet not depopulate the watery realms, the issue produced by some of their species is almost incredible. The spawn is not by scores, but by millions: and by this amazing expedient, constant reparation is made proportionable to the immense havoc.
As the different species of fishes are designed to occupy the waters, and range to and fro in that element, so they are wonderfully formed for that purpose. The chief instruments of the motion of a fish are the fins, which in some fishes are more numerous than in others. The fish in a state of repose, spreads all its fins, and seems to rest on its pectoral and ventral fins near the bottom: on folding the right pectoral fin, its body inclines to the right side; and on folding the left fin, it inclines to that side.—When the fish desires to have a retrograde motion, striking with the pectoral fins, in a contrary direction, effectually produces it. When the fish desires to turn, a blow from the tail sends it round; but if the tail strike both ways, then the motion is progressive. If the dorsal and ventral fins be cut off, the fish reels both to the right and left, and endeavors to supply its loss by keeping the rest of the fins in constant action. If the right pectoral fin be cut off, the fish leans to that side; if the ventral fin on the same side be cut off, then it loses its equilibrium entirely. When the tail is cut off, the fish loses all motion, and is carried wherever the water impels it.
In addition to the fins, an aquatic animal is furnished with an air bladder, a philosophical apparatus in its body; this sustains and enables it, at will to raise itself to the surface of the water, or, otherwise, to descend. When any accident has burst this air bladder, or it has been punctured by way of experiment, the fish remains at the bottom of the vessel or river, totally unable to ascend. Flounders, Soles and Skates, which are without this appendage, seldom rise in the water, and when they do, require a great effort. The simple action of the fins is not sufficient to raise the fish, its specific gravity being greater than the fluid in which it is immersed. The bag containing the air is supposed to be muscular, and when the air is compressed into a smaller compass by the action of this muscular power, the bulk of the fish is contracted with it; whereby, since the absolute weight remains the same, the specific gravity, which is the sinking force, is increased, and the fish sinks; when, on the contrary, this compression is removed, the air bladder expands, the fish is specifically lighter, and it ascends.