188 BRITISH FRESH-WATER FISHES 
In habits and appearance the grilse, on returning from the 
sea, is very similar to full-grown salmon, but persons accustomed 
to deal with these fish can discriminate with certainty between 
a 6 lb. salmon and a 10 Ib. grilse. The points of difference are 
as difficult to define in writing as those which distinguish a girl 
of sixteen from a woman of thirty. The grilse is smaller round 
the tail than the salmon, as you will find if you try to lift it by 
grasping it there; the tail fin is more forked; the snout is 
sharper; the general form of the fish is more elegant and the 
scales more delicate in the grilse stage than in later periods 
of growth. 
The salmon is what is termed an anadromous fish—that is, 
one that “ runs up”’—and it is usually stated that the purpose 
Habits of With which it ascends the rivers from the sea is that 
the Salmon. of reproduction. No doubt that is one motive, for 
salt water has been proved to be fatal to the vitality of the ova ; 
but to represent it as the only, or even the principal, motive is 
to misconstrue the facts of the life-history of the fish. In 
certain rivers, such as the Tay, salmon run from the sea in 
every month of the year; in others, they begin to run 
regularly in the spring months—February to May ; while in a 
third class of river they put in no appearance whatever till late 
in summer, or even in autumn. Now salmon appearing in 
“late” rivers, or appearing in the autumn in what are known 
as early rivers, do so in a more or less gravid condition, and 
may be said to be leaving the sea for the purpose of depositing 
their spawn ; but whereas the spawning season of salmon is 
perfectly defined as extending from the middle of October, at 
the earliest, to the end of January, how can it be said that fish 
running in the first quarter of the year are doing so for the 
purpose of spawning? The question will be further considered 
in the next chapter. 
Meanwhile, all that I wish to advance is that a portion, at 
least, of the spring and early summer run of salmon return 
to the sea long before the regular spawning season ; it is clear 
