NUTRITION AND GROWTH OF FISHES.
The nutritive functions of fishes follow the same order of progression as those of the other classes of the vertebrated kingdom. They seize, and in some measure divide, their food with their teeth; they digest it in the stomach, from whence it passes into the intestinal canal, where it receives a supply of bile from the liver, and frequently a liquid similar to that of the pancreas; the nutritive juices, absorbed by vessels analogous to lacteals, and probably taken up in part also directly by the veins, are mingled with the venous blood which is flowing towards the heart, from whence it is pushed to the branchiæ, in which, coming in contact with the water, it is converted into arterial blood, and then proceeds to the nourishment of the whole body.
Fishes are in general extremely voracious, and the rule of “eat or be eaten,” applies to them with unusual force. They are almost constantly engaged either in the active pursuit or patient waiting for their prey—their degree of power in its capture depending, of course, on the dimensions of the mouth and throat, and the strength of the teeth and jaws. If the teeth are sharp and curved, they are capable of seizing and securing either a large and fleshy bait, or the slenderest and most agile animal; if these parts are broad and strong, they are able to bruise the hardest aliment; if they are feeble or almost wanting, they are only serviceable in procuring some inert or unresisting prey. Fishes indeed, in most instances, show but little choice in the selection of their food, and their digestive powers are so strong and rapid as speedily to dissolve all animal substances. They greedily swallow other fishes, notwithstanding the sharp spines or bony ridges with which they may be armed; they attack and devour crabs and shell-fish, gulping them entire, without the least regard to the feelings of their families; they do not object occasionally to swallow the young even of their own species, and the more powerful kinds carry their warfare into other kingdoms of nature, and revel on rats, reptiles and young ducklings, to say nothing, gentle reader, of the ferocious shark, which not seldom makes a meal even of the lord of the creation. A particular friend of ours has his right leg in the West Indies, in consequence of an act of aggression alike unpleasant and uncalled for, and which a Christian-minded pedestrian finds it easier to forgive than forget. The species which live chiefly on vegetables are few in number, almost all fishes preferring pork to green peas.
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.