Fishes in general are male and female; the former possessing the melt and the latter the roe, although some individuals of the cod and sturgeon are said to contain both. The spawn of the greater number of fishes is deposited in the sand or gravel; and in that state, it is probable that the roe and melt are mixed together. A fish whose weight, at twenty years old, shall be thirty pounds, generates the first or second year, when perhaps it does not weigh more than half a pound; and it is certain that the male seems more attached to the eggs than the female, for when she ceases to drop them, the male instantly abandons her, and with ardour follows the eggs which are carried down by the stream, or dispersed amongst the waves by the wind, passing and repassing many times over every spot where he finds the eggs.
Summer is the usual spawning time, because at that season the water is tepified by the beams of the sun, and is therefore better adapted for quickening the eggs into life. How the eggs of fishes are impregnated is wholly unknown. All that obviously offers is, that in ponds, the sexes are often seen together among the long grass at the edge of the water; that there they seem to struggle, and are in a state of suffering, as they grow thin, lose their appetite, whilst their flesh becomes flabby, and in some, the scales grow rough and lose their lustre; on the contrary, when the time of coupling is over, their appetite returns, their natural agility is resumed, and their scales become brilliant and beautiful. The spawn continues in the state of eggs a longer or shorter period, but this is for the most part proportioned to the size of the animal. The young animal remains in the form of an egg from December until April in the salmon kind; the carp not above three weeks, and the gold fish from China is produced in a still less time. With all the advantages of minuteness and agility when excluded from the egg, there is not one, perhaps, of a thousand, that survives the dangers of its youth. Among the spinous fishes there is no trace of parental affection; they abandon their eggs to be hatched by the warmth of the season, and if they ever return to the spot where their young first received life, the parents that gave them birth, become their most formidable enemies.
By the rapacity of one another although the fishes perish by millions, yet they have other destroyers. Many of the quadrupeds and a great proportion of the sea fowls, either feed on fish, are the merciless invaders of the small fry, or devour the spawn. In a savage state, numbers of the human race wander round the lakes and rivers, whence a considerable proportion of their sustenance is derived, and among those nations whom arts and agriculture have rendered less dependent on this precarious support, superstition has usurped the place of want, and given a new edge to their avidity for this species of food; but the munificent Author of nature, notwithstanding the annual consumption of fishes is constant and immense, has made a kind provision for his creatures, in which the glory of his providence is remarkable in a twofold manner. First, by giving fishes at certain fixed seasons of the year, a particular inclination to approach the land; and this always at a time when they are the fattest, and not emaciated by breeding; as the salmon in the spring, mackerel about midsummer, herrings in the autumn, cod in the winter, &c. Secondly, by the amazing fertility which he has conferred on this class of beings. The fecundity of fishes far surpasses that of any other animals; if we should be told of a being so prolific, that it would bring forth in one season as many of its kind as there are inhabitants in England, our surprise would be deeply excited, yet upwards of 9,000,000 of ova have been found in the spawn of a single cod. 1,357,400 have been taken from the belly of a flounder; the mackerel, carp, tench, and a variety of others, are endowed with a fertility but little inferior. Such an astonishing progeny, were it allowed to arrive at maturity, would soon overstock the element allotted them; but their numbers, by the means above-mentioned, are considerably lessened, and thus two important purposes are answered in the economy of nature; by the extraordinary fruitfulness of fishes, amongst a host of foes it preserves the species, and furnishes the rest with an aliment adapted to their nature.
Fishes are the most voracious animals in nature. Many species prey indiscriminately on everything digestible that comes in their way, and devour not only other species of fishes, but even their own. As a counter-balance to this voracity, they are amazingly prolific. Some bring forth their young alive; others produce eggs. The viviparous blenny brings forth 200 or 300 live fishes at a time. Those which produce eggs are all much more prolific, and seem to proportion their stock to the danger of consumption. Leuwenhoek affirms that the cod spawns above 9,000,000 in a season. The flounder produces above 1,000,000, and the mackerel above 500,000. Scarcely one in a hundred of these eggs, however, is supposed to come to maturity; but two wise purposes are answered by this amazing increase: it preserves the species in the midst of numberless enemies, and serves to furnish the rest with a sustenance adapted to their nature.
How long a fish, that seems to have scarce any bounds put to its growth, continues to live, is not ascertained; the date prescribed as the age of man, would not perhaps be sufficient to measure the life of the smallest. In the royal ponds at Marli, in France, there are some fishes that have been preserved tame since the time, it is said, of Francis the First, and which have been individually known to the persons who have succeeded to the charge of them, ever since that period. These have now attained a size much beyond the common bulk of fishes of the same kind; and although there are certain peculiarities distinguishing them from younger fishes, yet they evince no symptoms of that decrepitude and disease, which inevitably accompany a life protracted much beyond the usual space, among quadrupeds.
When any fish is hog-backed, with a small head, this is a sure sign of that fish being in season, of whatever sort it is.