Footnote 17: [(return)]
Mr Young has, however, likewise repeated and confirmed Mr Shaw's earlier experiments regarding the slow growth of salmon fry in fresh water, and the conversion of parr into smolts. We may add, that Sir William Jardine, a distinguished Ichthyologist and experienced angler, has also corroborated Mr Shaw's observations.
Footnote 18: [(return)]
These two specimens are now preserved in the Museum of the Royal Society of Edinburgh.
Footnote 19: [(return)]
The existence in the rivers during spring, of grilse which have spawned, and which weigh only three or four pounds, is itself a conclusive proof of this retardation of growth in fresh water. These fish had run, as anglers say—that is, had entered the rivers about midsummer of the preceding year—and yet had made no progress. Had they remained in the sea till autumn, their size on entering the fresh waters would have been much greater; or had they spawned early in winter, and descended speedily to the sea, they might have returned again to the river in spring as small salmon, while their more sluggish brethren of the same age were still in the streams under the form of grilse. All their growth, then, seems to take place during their sojourn in the sea, usually from eight to twelve weeks. The length of time spent in the salt waters, by grilse and salmon which have spawned, corresponds nearly to the time during which smolts remain in these waters; the former two returning as clean salmon, the last-named making their first appearance in our rivers as grilse.
Footnote 20: [(return)]
These two specimens, with their wire marks in situ, may now be seen in the Museum of the Royal Society of Edinburgh.
Footnote 21: [(return)]
Mr Shaw, for example, states the following various periods as those which he found to elapse between the deposition of the ova and the hatching of the fry—90, 101, 108, and 131 days. In the last instance, the average temperature of the river for eight weeks, had not exceeded 33°.
Footnote 22: [(return)]
If we are rightly informed, salmon were not in the habit of spawning in the rivulets which run into Loch Shin, till under the direction of Lord Francis Egerton some full-grown fish were carried there previous to the breeding season. These spawned; and their produce, as was to be expected, after descending to the sea, returned in due course, and, making their way through the loch, ascended their native tributaries.
Footnote 23: [(return)]
A complete series of specimens, from the day of hatching till about the middle of the sixth year, has been deposited by Mr Shaw in the Museum of the Royal Society of Edinburgh.
Footnote 24: [(return)]
Mr Shaw informs us, moreover, that if those individuals which have assumed the silvery lustre be forcibly detained for a month or two in fresh water, they will resume the coloured coating which they formerly bore. The captive females, he adds, manifested symptoms of being in a breeding state by the beginning of the autumn of their third year. They were, in truth, at this time as old as herlings, though not of corresponding size, owing to the entire absence of marine agency.
Footnote 25: [(return)]
Another interesting result may be noticed in connexion with this Compensation Pond. The original streamlet, like most others, was naturally stocked with small "burn-trout," which never exceeded a few ounces in weight, as their ultimate term of growth. But, in consequence of the formation above referred to, and the great increase of their productive feeding-ground, and tranquil places for repose and play, these tiny creatures have, in some instances, attained to an enormous size. We lately examined one which weighed six pounds. It was not a sea-trout, but a common fresh-water one—Salmo fario. This strongly exemplifies the conformable nature of fishes; that is, their power of adaptation to a change of external circumstances. It is as if a small Shetland pony, by being turned into a clover field, could be expanded into the gigantic dimensions of a brewer's horse.
Footnote 26: [(return)]
The specimen is preserved in the Museum of the Royal Society of Edinburgh.