teriorate 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]

[18] These two specimens are now preserved in the Museum of the
Royal Society of Edinburgh.

[19] 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.

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 t