We may now proceed to consider the final change,—that of the grilse into the adult salmon. We have just seen that smolts return to the rivers as grilse, (of the weights above noted,) during the summer and autumn of the same season in which they had descended for the first time to the sea. Such as seek the rivers in the earlier part of summer are of small size, because they have sojourned for but a short time in the sea:—such as abide in the sea till autumn, attain of course a larger size. But it appears to be an established, though till now an unknown fact, that with the exception of the early state of parr, in which the growth has been shown to be extremely slow, salmon actually never do grow in fresh water at all, either as grilse or in the adult state. All their growth in these two most important later stages, takes place during their sojourn in the sea. "Not only," says Mr Young, "is this the case, but I have also ascertained that they actually decrease in dimensions after entering the river, and that the higher they ascend the more they deteriorate both in weight and quality. In corroboration of this I may refer to the extensive fisheries of the Duke of Sutherland, where the fish of each station of the same river are kept distinct from those of another station, and where we have had ample proof that salmon habitually decrease in weight in proportion to their time and distance from the sea."[19]

Mr Young commenced marking grilses, with a view to ascertain that they became salmon, as far back as 1837, and has continued to do so ever since, though never two seasons with the same mark. We shall here record only the results of the two preceding years. In the spring of 1841, he marked a number of spawned grilse soon after the conclusion of the spawning period. Taking his "net and coble," he fished the river for the special purpose, and all the spawned grilse of 4 lb. weight were marked by putting a peculiarly twisted piece of wire through the dorsal fin. They were immediately thrown into the river, and of course disappeared, making their way downwards with other spawned fish towards the sea. "In the course of the next summer we again caught several of those fish which we had thus marked with wire as 4 lb. grilse, grown in the short period of four or five months into beautiful full-formed salmon, ranging from 9 lb. to 14 lb. in weight, the difference still depending on the length of their sojourn in the sea."

In January 1842, he repeated the same process of marking 4 lb. grilse which had spawned, and were therefore about to seek the sea; but, instead of placing the wire in the back fin, he this year fixed it in the upper lobe of the tail, or caudal fin. On their return from the sea, he caught many of these quondam grilse converted into salmon as before. The following lists will serve to illustrate the rate of growth:—

List of Grilse marked after having spawned, and re-captured as Salmon, on their second ascent from the Sea.

Period of marking. Period of recapture. Weight when marked. Weight when retaken.
1841. Feb. 18. 1841. June 23. 4 lbs.9 lbs.
18. 23. 4 lbs.11 lbs.
18. 25. 4 lbs.9 lbs.
18. 25. 4 lbs.10 lbs.
18. July 27. 4 lbs.13 lbs.
18. 28. 4 lbs.10 lbs.
March 4. July 1. 4 lbs.12 lbs.
4. 1. 4 lbs.14 lbs.
4. 27. 4 lbs.12 lbs.
1842. Jan. 29. 1842. July 4. 4 lbs.8 lbs.[20]
29. 14. 4 lbs.9 lbs.[20]
29. 14. 4 lbs.8 lbs.
March 8. 23. 4 lbs.9 lbs.
Jan. 29. 29. 4 lbs.11 lbs.
March 8. Aug. 4. 4 lbs.10 lbs.
Jan. 29. 11. 4 lbs.12 lbs.

During both these seasons, Mr Young informs us, he caught far more marked grilse returning with the form and attributes of perfect salmon, than are recorded in the preceding lists. "In many specimens the wires had been torn from the fins, either by the action of the nets or other casualties; and, although I could myself recognise distinctly that they were the fish I had marked, I kept no note of them. All those recorded in my lists returned and were captured with the twisted wires complete, the same as the specimens transmitted for your examination."

We agree with Mr Young in thinking that the preceding facts, viewed in connexion with Mr Shaw's prior observations, entitle us to say, that we are now well acquainted with the history and habits of the salmon, and its usual rate of growth from the ovum to the adult state. The young are hatched after a period which admits of considerable range, according to the temperature of the season, or the modifying character of special localities.[21] They usually burst the capsule of the egg in 90 to 100 days after deposition, but they still continue for a considerable time beneath the gravel, with the yelk or vitelline portion of the egg adhering to the body; and from this appendage, which Mr Shaw likens to a red currant, they probably derive their sole nourishment for several weeks. But though the lapse of 140 or even 150 days from the period of deposition is frequently required to perfect the form of these little fishes, which even then measure scarcely more than an inch in length, their subsequent growth is still extremely slow; and the silvery aspect of the smolt is seldom assumed till after the expiry of a couple of years. The great mass of these smolts descend to the sea during the months of April and May,—the varying range of the spawning and hatching season carrying with it a somewhat corresponding range in the assumption of the first signal change, and the consequent movement to the sea. They return under the greatly enlarged form of grilse, as already stated, and these grilse spawn that same season in common with the salmon, and then both the one and the other re-descend into the sea in the course of the winter or ensuing spring. They all return again to the rivers sooner or later, in accordance, as we believe, with the time they had previously left it after spawning, early or late. The grilse have now become salmon by the time of their second ascent from the sea; and no further change takes place in their character or attributes, except that such as survive the snares of the fishermen, the wily chambers of the cruives, the angler's gaudy hook, or the poacher's spear, continue to increase in size from year to year. Such, however, is now the perfection of our fisheries, and the facilities for conveying this princely species even from our northern rivers, and the "distant islands of the sea," to the luxurious cities of more populous districts, that we greatly doubt if any salmon ever attains a good old age, or is allowed to die a natural death. We are not possessed of sufficient data from which to judge either of their natural term of life, or of their ultimate increase of size. They are occasionally, though rarely, killed in Britain of the weight of forty and even fifty pounds. In the comparatively unfished rivers of Scandinavia large salmon are much more frequent, although the largest we ever heard of was an English fish which came into the possession of Mr Groves, of Bond Street. It was a female, and weighed eighty-three pounds. In the year 1841, Mr Young marked a few spawned salmon along with his grilse, employing as a distinctive mark copper wire instead of brass. One of these, weighing twelve pounds, was marked on the 4th of March, and was recaptured on returning from the sea on the 10th of July, weighing eighteen pounds. But as we know not whether it made its way to the sea immediately after being marked, we cannot accurately infer the rate of increase. It probably becomes slower every year, after the assumption of the adult state. Why the salmon of one river should greatly exceed the average weight of those of another into which it flows, is a problem which we cannot solve. The fact, for example, of the river Shin flowing from a large lake, with a course of only a few miles, into the Oykel, although it accounts for its being an early river, owing to the receptive depth, and consequently higher temperature of its great nursing mother, Loch Shin, in no way, so far at least as we can see, explains the great size of the Shin fish, which are taken in scores of twenty pounds' weight. They have little or nothing to do with the loch itself, haunting habitually the brawling stream, and spawning in the shallower fords, at some distance up, but still below the great basin;[22] and there are no physical peculiarities which in any way distinguish the Shin from many other lake born northern rivers, where salmon do not average half the size.

Leaving the country of the Morer Chatt (the Celtic title of the Earls of Sutherland) we shall now return to the retainer of the "bold Buccleuch." We have already mentioned that Mr Shaw, having so successfully illustrated the early history of salmon, next turned his attention to a cognate subject, that of the sea-trout (Salmo-trutta?) Although no positive observations of any value, anterior to those now before us, had been made upon this species, it is obvious that as soon as his discoveries regarding salmon fry had afforded, as it were, the key to this portion of nature's secrets, it was easy for any one to infer that the old notions regarding the former fish were equally erroneous. Various modifications of these views took place accordingly; but no one ascertained the truth by observation. Mr Shaw was, therefore, entitled to proceed as if the matter were solely in his own hands; and he makes no mention either of the "vain imaginations" of Dr Knox, the more careful compilation of Mr Yarrell, or the still closer, but by no means approximate calculations of Richard Parnell, M.D. In this he has acted wisely, seeing that his own essay professes to be simply a statement of facts, and not an historical exposition of the progress of error.

It would, indeed, have been singular if two species, in many respects so closely allied in their general structure any economy, had been found to differ very materially in any essential point. It now appears, however, that Mr Shaw's original discovery of the slow growth of salmon fry in fresh water, applies equally to sea trout; and, indeed, his observations on the latter are valuable not only in themselves, but as confirmatory of his remarks upon the former species. The same principle has been found to regulate the growth and migrations of both, and Mr Shaw's two contributions thus mutually strengthen and support each other.

The sea trout is well known to anglers as one of the liveliest of all the fishes subject to his lure. Two species are supposed by naturalists to haunt our rivers—Salmo eriox, the bull trout of the Tweed, comparatively rare on the western and northern coasts of Scotland, and Salmo trutta, commonly called the sea or white trout, but, like the other species, also known under a variety of provincial names, somewhat vaguely applied. In its various and progressive stages, it passes under the names of fry, smolt, orange-fin, phinock, herling, whitling, sea-trout, and salmon-trout. It is likewise the "Fordwich trout" of Izaak Walton, described by that poetical old piscator as "rare good meat." As an article of diet it indeed ranks next to the salmon, and is much superior in that respect to its near relation, S. eriox. It is taken in the more seaward pools of our northern rivers, sometimes in several hundreds at a single haul; and vast quantities, after being boiled, and hermetically sealed in tin cases, are extensively consumed both in our home and foreign markets. But, notwithstanding its great commercial value, naturalists have failed to present us with any accurate account of its consecutive history from the ovum to the adult state. This desideratum we are now enabled to supply through Mr Shaw.