196 BRITISH FRESH-WATER FISHES 
the female deposits such of her ova as are ripe for shedding, 
beginning, it is said, at the lower end of the trough. The 
male moves up and sheds his milt upon them, and, as the fish 
work up stream, the action of their fins and tail bury the eggs 
as fast as they are impregnated. This process is repeated daily 
until all the ova are deposited. Generally there are a pair 
of salmon, male and female, of about equal size on each 
redd ; but in addition to these, smaller males hang about, 
endeavouring to snatch an occasion for cutting in. The 
result has been described by several observers as a series 
of fierce tiltings between the rivals, many of whom lose 
their lives in combat. 
The period of spawning varies slightly according to 
latitude, fish in the extreme north of Scotland being from 
a fortnight to a whole month in advance of those in rivers 
further south. Thus in the autumn of 1899 the first 
salmon were seen upon the redds of the Tay on November rst, 
of the Forth on November 8th, of the Helmsdale on 
October 10th, and of the Findhorn on October 17th. The 
months when the majority of salmon spawn in most rivers 
are those of November and December. 
The spawn is exposed to many accidents after it has been 
deposited in the redds in the manner described. Trout, 
eels, and coarse fish eat the ova greedily ; in fact, salmon roe 
is known to be such a deadly bait for trout that its use has 
long been prohibited by law. Birds and water insects of 
several species prey on this succulent fare ; pollution, especially 
of a sedimentary nature, is very hurtful to the ova; but 
perhaps the greatest destruction of all is wrought by ice in 
very hard winters. It is not that the eggs are destroyed by 
cold ; they will stand exposure to a very low temperature ; 
but the ground ice, which is formed in running water by 
severe frost, rises when the fresh comes, carrying with it 
masses of gravel and all that it contains. Nature, as usual, 
has counterbalanced the risks of destruction by the fecundity of 
