The growth of these creatures depends greatly on the nature and amount of food, different individuals of the same species exhibiting a large disparity in their dimensions. They grow less rapidly in small ponds or shallow streams, than in large lakes and deep rivers. We once kept a minnow, little more than half an inch long, in a small glass vessel for a period of two years, during which time there was no perceptible increase in its dimensions. Had it continued in its native stream, subjected to the fattening influence of a continuous flow of water, and a consequent increase in the quantity and variety of its natural food, its cubic dimensions would probably have been twenty times greater; yet it must have attained, long prior to the lapse of a couple of years, to the usual period of the adult state. The growth itself seems to continue, under favorable circumstances, for a length of time, and we can scarcely set bounds to, certainly we know not with precision, the utmost range of the specific size of fishes. Salmon sometimes attain a weight of eighty pounds and upwards, and the giant pike of Kaiserslautern is alleged to have measured nineteen feet, and to have weighed 350 pounds. No doubt, an incorrect allegation does not in any way increase the actual size of fishes, and few people now-a-days can take exact cognizance of what was done at Mannheim in the year 1497; but, even in these degenerate days, amid our own translucent waters, and among species in no way remarkable for their ordinary dimensions, we ever and anon meet with ancient individuals which vastly exceed the usual weight and measure of their kind. But, in spite of this, let no angler, whether in the bloom of early youth, the power of matured manhood, or with the silver locks of “hoar antiquity” above his wrinkled brow, ever induce within himself, or express to others, the belief that, at all times and places, he is perpetually catching enormous trouts in vast numbers, because we happen to know that this is not the case. We don’t insist upon any one weighing every fish he captures, but we insist that no one, after jerking out a few pair, will maintain next morning, or even that very night, that he has had a most toilsome but very glorious day, and has killed five dozen and four of the finest trouts the human eye ever gazed upon. “All men are liars”—and several anglers—is a proposition the exact import of which depends much on the mode of construction.
THE MUSCULAR MOVEMENTS OF FISHES.
The vertebral column, composed of numerous articulations, united by cartilages which permit of certain movements, curves with great facility from side to side; but the vertical motion is much more restricted, chiefly in consequence of the projection of the upper and under spiny processes of the vertebræ. The great organ of movement in all fishes is the tail. The muscles, by which it is brought into play, extend in lengthened masses on either side of the vertebral column. The body, being supported chiefly by the swimming bladder, (which, however, is absent in several species), is propelled forward by the rapid flexure of the extremity acting laterally upon the resistance offered by the water. Generally speaking, neither the pectoral nor the ventral fins are of any material use during swift progressive motion; they rather serve to balance the body, or to aid its gentler movements while in a state of comparative repose. In flying fishes, as they are called, the pectoral fins are of such great length and expansion as to support these creatures in the air; and the strength of muscular action might probably suffice even for a longer flight, but for the necessity of constant moisture for the purposes of respiration. The drying of the gills in an individual of this class is attended by results analogous to those produced in the case of a land animal; and a flying fish is obliged to descend to respire, in like manner as a swimming quadruped, or disguised mammiferous animal, as we may term a whale, is under the necessity of ascending for the same purpose.
The heads of fishes exercise but a slight movement independent of the rest of the body, but the jaws, opercular bones, branchial arches, and other parts, are very free in their motions. The muscles, like those of other vertebrated animals, are composed of fleshy fibres more or less colored, and of tendonous fibres of a white or silvery aspect. With the exception, however, of certain spinal muscles, which are sometimes of a deep red, the flesh of fishes is much paler than that of quadrupeds, and still more so than that of birds. In several species it is even entirely white.
THE NERVOUS SYSTEM AND SENSES OF FISHES.
As fishes respire through the intervention of water alone, that is, as they can scarcely avail themselves, in rendering their blood arterial, of anything more than the small portion of oxygen contained in the air which is suspended in the water, their blood is necessarily cold, and the general energy and activity of their senses are by no means so great as those of quadrupeds and birds. Their brain also, though of similar composition, is proportionally much smaller, whether as compared with the total size of the body, with the mass of nerves which proceed from it, or with the cavity of the cranium in which it is contained. In the turbot (Gadus lota) for example, the weight of the brain to that of the spinal marrow is ascertained to be as 8 to 12, and to that of the whole body as 1 to 720; and it has been ascertained that the brain of a pike, weighed in proportion to the whole body, is as 1 to 1305. Now, in many small birds, the brain, viewed in relation to the rest of the body, is equal to a twentieth part. In the generality of fishes, the spinal cord extends along the whole of the caudal vertebræ, and it is thus that it preponderates over the brain; but the fishing frog, or sea devil (Lophius piscatorius), the moon fish (Lampris guttatus), and a few others, form exceptions to this rule, the spinal marrow disappearing before it reaches the eighth vertebra. The brain of fishes by no means fills up the cavity of the cranium; and the interval between the pia mater, which envelopes the brain itself, and the dura mater, which lines the interior of the skull, is occupied only by a loose cellulosity, frequently impregnated by an oil, or sometimes, as in the sturgeon and thunny, by a more compact fatty matter. It has also been remarked that this void between the cranium and the brain is much less in young subjects than in adults; from which it may be inferred that the brain does not increase in an equal proportion with the rest of the body. Cuvier, in fact, has found its dimensions nearly the same in different individuals—of the same species—of which the general size of one was double that of the other.
Although we should be sorry to lower the subjects of our present observation in the estimation of society, we think it undeniable that, of all vertebrated animals, fishes exhibit the smallest apparent symptoms of refined sensibility. Having no elastic air to act upon, they are necessarily mute, or nearly so, and all the sweet sensations which the delightful faculty of voice has called into being among the higher tribes, are to them unknown. Their glazed, immovable eyes, their fixed and bony faces, admit of no playful range in their physiognomical expression, of no variation connected with emotion. Their ears, surrounded on every side by the bones of the cranium, destitute of external conch, without any internal cochlea, and composed merely of certain sacks and membranous canals, scarcely suffice for the perception of the loudest sounds. Yet they will sink affrighted into the darksome depths of lakes, beneath the banks of rivers, or in oceans blue profound, when the “sky lowers and mutters thunder,” and with elemental fierceness the sheeted lightning flashes broad and bright above their liquid dwellings.