The Harvest of the Sea / A contribution to the natural and economic history of the British food fishes

by James Glass Bertram

Any of my readers who wish to manipulate these figures may try by way of experiment a few calculations with the herring. The produce of a single herring is, let us say, thirty-six thousand eggs, but we may—and the deduction is a most reasonable one—allow that half of these never come to life, which reduces the quantity born to eighteen thousand. Allowing that the young fish will be able to repeat the story of their birth in three years, we may safely calculate that the breeding stock by various accidents will by that time be reduced to nine thousand individuals; and granting half of these to be females, or let us say, for the sake of rounding the figures, that four thousand of them yield roe, we shall find by multiplying that quantity by thirty-six thousand (the number of eggs in a female herring) that we obtain a total of one hundred and forty-four millions as the produce in three years of a single pair of herrings; and although half of these might be taken as the food of man as soon as they were large enough, there would still be left an immense breeding stock even after all deductions for casualties had been given effect to; so that the devastations committed by man on the shoals while capturing for food uses must be enormous if they affect, as I suppose, the reproductiveness of these useful animals. Of course this is but guess-work, and is merely given as a basis for a more minute statement; but I have conversed with practical people who do not think that, taking all times and seasons into account, even five per cent of the roe of a herring comes to life, far less that such a percentage reaches maturity as table fish.

It is now well enough known, even to the merest tyros in the study of natural history, and to anglers and others interested as well, that the impregnation of fish-eggs is a purely external act; but at one time this was not believed, and even so lately as six years ago a portion of the experiments at the Stormontfield salmon-breeding ponds was dedicated, by Mr. Robert Buist, to a solution of this question, with what result may be easily guessed. The old theory, so stoutly maintained by Mr. Tod Stoddart and others, that it is contrary both to fact and reason that fish can differ from land animals in the matter of the fructification of their eggs, was signally defeated, and the question conclusively settled at the ponds in a very simple way—namely, by placing in the breeding-boxes a quantity of salmon eggs which had not been brought into contact with the milt, and which rotted away; proving emphatically that the sexes do not come into alliance at the time of spawning, and that there is no way of rendering the eggs fruitful unless they are brought into immediate contact with the milt. Curious ideas used to prevail on this branch of natural history. Herodotus observes of the fish of the Nile, that at the season of spawning they move in vast multitudes towards the sea; the males lead the way, and emit the engendering principle in their passage; this the females absorb as they follow, and in consequence conceive, and when their ova are deposited they are consequently matured into fry. Linnæus backed up this idea, and asserted that there could be no impregnation of the eggs of any animal out of the body, and as fish have no organs of generation, there was in the mind of the great naturalist no more feasible explanation of their mode of reproduction than that given in Beloe’s Herodotus. It is this wonderfully exceptional principle in the life of fish that has given rise to the art of pisciculture—i.e. the artificial impregnation of the eggs of fish forcibly exuded from these animals, which, as will be fully explained in another portion of this work, are brought into contact with the milt, independent altogether of the animal.

The principle of fish life which brings the male and female together at the period of spawning is unknown. It is supposed by some naturalists that fish do not gather into shoals till they are about to perform the grandest action of their nature, and that till that period each animal lives a separate and individual life. If we set down the sense of smell as the power which attracts the fish sexes, we shall be very nearly correct: such cold-blooded animals cannot very well have any more powerful instinct. A very clever Spanish writer on pisciculture hints that the fish have no amatory feeling for each other at that period, thus forming a curious exception to most other animals, and that it is the smell of the roe in the female that attracts the male. As the writer well expresses it—“The curious phenomenon of the fecundation of the eggs or spawn of the female fish away from the bowels of the mothers, and independent of their co-operation in every way, constitutes an interesting exception to the almost universal law of instinct and sympathy in the sexes—a law simple in its essence, as are all nature’s laws, but most prolific in its results; for we see it pass through all the phases of an immense series, from the phenomena of organic attraction shown by the first-named living beings up to the great passions of love and maternity in the human species, forming the affectionate and solid bases of families and the imperishable foundation of society.”

This idea—viz. as to the shoaling of the fish at the period of spawning only—has been prominently thrown out in regard to the herring by parties who do not admit even of a partial migration from the deep to the shallow water, which, however, is an idea that is stoutly held by some writers on the herring question. It is rather interesting, however, in connection with this phase of fish life, to note that particular shoals of herrings deposit their spawn at particular places, that the eggs come simultaneously to life, and that it is quite certain that the young fish remain together for a considerable period—a few months at least—after they are hatched. This is well known from the fact of large bodies of young herrings having been caught during the sprat season; these could not, of course, have been assembled to spawn—they were too young and had no development of milt or roe. This, if these fish separate, gives rise to the question—At what period do the herrings begin their individual wanderings? Sprats, of course—if sprats be sprats and not the young of the herring—may have come together at the period when they are so largely captured for the purpose of perpetuating their kind; but if so, they must live long together before they acquire milt or roe. And how is it that we so often find young herrings in the sprat shoals? Then, again, how comes it that the fishermen do not frequently fall in with the separate herrings during the white-fishing seasons? How is it that fishermen find particular kinds of fish always on particular ground? How is it that eels migrate in immense bodies? My opinion is, that particular kinds of fish do hold always together, or at all events gather at particular seasons into greater or lesser bodies. No doubt, life among the inhabitants of the sea, if we could know it, is quite as diversified as life on land, where we observe that many kinds of animals colonise—ants, bees, etc. Are the old stories about each kind of fish having a king so absolutely incredible after all? That there are schools of fish is certain; how the great bodies may be divided can only be guessed.

Whatever may be the attracting cause, and however powerful the sexual instinct may be among fish, it can scarcely be discussed fully in a work which makes no pretension to being scientific or even technological. It is noteworthy, however, that fish-eggs afford us an admirable opportunity of studying a peculiarly interesting stage of animal life—viz. the embryo stage—which naturally enough is rather obscure in all animals. Having had opportunities of observing the eggs of the salmon in all their stages of progress, from the period of their first contact with the milt till the bursting of the egg and the coming forth of the tiny fish, I will venture briefly to describe what I have seen, because salmon eggs are of a convenient size for continued examination. The roe of this fine fish is, I daresay, pretty familiar to most of my readers. The microscope reveals the eggs of the salmon as being more oval than round, although they appear quite round to the naked eye. A yolk seems to float in the dim-looking mass, and the skin or shell appears full of minute holes, while there is an appearance of a kind of canal or funnel, which opens from the outside and is apparently closed at the inner end. The milt is found to swarm with a species of very small creatures with big heads and long tails, apparently of very low organisation. On the contact of this fluid with the egg, into which it enters by the canal I have described, an immediate change takes place—the ovum, so to speak, becomes illuminated as if by some curious internal power, and the aspect of the egg then appears a great deal brighter and clearer than before; and it is surely wonderful that on the mere touching of the egg with this wonder-working sperm so great a change should take place—a change which indicates that the grand process of reproduction characteristic of all living nature has begun in the ovum, and will go on with increasing strength to maturity.

Beds containing salmon-spawn are so accessible, comparatively speaking, as to render it easy to trace the development of the egg from the embryo to the complete animal. I have personally watched the egg from the date of its contact with the milt till the little salmon has burst out of its fragile prison and waddled away to the shady side of a friendly pebble, evidently anxious to hide its nakedness. I was enabled, in fact, to hatch a few salmon eggs, brought from Stormontfield last Christmas-day, by means of a very simple apparatus in a printing-office, and had therefore an opportunity of daily observation. As may be supposed, however, the transmutation of a salmon egg into a fish is a tedious process, which takes above a hundred days to accomplish. The eggs of the female under the natural system of spawning are laid in the secluded and shallow tributary of some choice stream, in a trough of gravel ploughed up by the fish with great labour, and are there left to be wooed into life by the eternal murmuring of the water. From November till March, through the storms and floods of winter, the ova lie hid among the gravel, slowly but surely quickening into life, and few persons would guess from a mere casual glance at the tributary of a great salmon stream that it held among its bubbling waters such a countless treasure of future fish. A practised person will find out a burrow of salmon eggs with great precision, and a little bit of water may contain perhaps a million of eggs waiting to be summoned into life by the mysterious workings of nature. During the first three weeks from the milting of the egg scarcely any change is discernible in its condition, except that about the end of that period it contains a brilliant spot, which gradually increases in its brilliancy, when certain threads of blood begin faintly to prefigure the anatomy of the young fish. After another day or two, the bright spot seems to assume a ring-like form, having a clear space in the centre, and the blood-threads then become more and more apparent. These blood-like tracings are ultimately seen to take an animal shape; but it would be difficult at first to say what the animal may turn out to be—whether a tadpole or a salmon. After this stage of the development is reached, two bright black specks are then seen—the eyes of the fish. We can now, from day to day, note the form as it gradually assumes a more perfect shape; we can see it change palpably almost from hour to hour. After the egg has been laved by the water for a hundred days, we can observe that the young fish is then thoroughly alive and, to use a common expression, kicking. We can see it moving and can study its anatomy, which, although as yet very rudimentary, contains all the elements of the perfect fish. Heat expedites the birth of the fish. The eggs of a minnow have been sensibly advanced towards maturity by being held on the palm of the hand. The spawn of the lobster has the advantage of being nursed on the tail of the animal till it is just on the point of ripening into life. Salmon eggs deposited early in the season, when the temperature is high, come sooner to life than those spawned in mid-winter: indeed there is a difference of as much as fifty days between those deposited in September and those spawned in December, the one requiring ninety days, the other one hundred and forty days to ripen into life. Salmon have been brought to life in sixty days at Huningue; but the quickest hatching ever accomplished at the Stormontfield breeding-ponds was when the fish came to life in one hundred and twenty days.

I have endeavoured to illustrate these early stages of fish life by a drawing, which shows the eggs at about their natural size, as also the advance of the fish in size and shape.

EGGS OF THE SALMON KIND JUST HATCHING.

At the salmon-ponds of Stormontfield the eggs laid down the first season were hatched in one hundred and twenty-eight days, but the eggs of other fish have been known to come to life a great deal sooner. The usual time for the hatching of salmon eggs in our northern rivers is one hundred and thirty days, or between four and five months, according to the openness or severity of the season. When at last the infant animal bursts from the shell, it is a clumsy, unbalanced, tiny thing, having attached to it the remains of the parental egg, which hamper its movements; but after all, the remains of its little prison are exceedingly useful, as for a space of about thirty days the young salmon cannot obtain other nourishment than what is afforded by this umbilical bag.