206 BRITISH FRESH-WATER FISHES 
2. The protection of the fertilised ova from ice, floods, 
and destruction by predaceous animals of many kinds. About 
the superior results of artificial hatching in this respect there 
can be no doubt whatever. From go to 95 per cent. of the 
ova laid down may be expected to hatch under careful manage- 
ment, whereas in the natural beds it is impossible to calculate 
the proportion that may be devoured or otherwise destroyed 
during incubation, 
3. The protection of the alevins during the tender period 
while the umbilical bag is being absorbed, when they are as 
defenceless as eggs themselves, and in the further stage of fry. 
In this point also the advantage is all on the side of artificial 
culture, but the ultimate benefit to the fishery depends almost 
entirely upon whether the fry are turned loose at once or 
protected during a second winter until ready to make their 
migration to the sea. 
4. The certainty of a full and constant hatch of fry inde- 
pendent of such conditions as scarcity of spawners, severe 
winters, and other untoward circumstances. In this the 
advantage certainly is with the hatchery. 
The objections to artificial propagation are as follows :— 
1. The disturbance of the spawning beds by netting the 
spawners. This is a very serious consideration. Every well- 
managed hatchery should be provided with the means of 
taking fish before they go on the redds, impounding them in 
suitable tanks or pools, where they may lie quiet until ready 
to shed their spawn. Fish spawning on the natural ground 
should be disturbed under no circumstances whatever. 
2. The depletion of the natural stock of a river in order 
to substitute a stock reared artificially, and consequently less 
capable of encountering the vicissitudes of salmon life. I do 
not regard this objection as of any weight. The depletion 
caused by stripping spawners is amply compensated for by the 
far greater number of young brought safely through the egg, 
alevin, and fry stages ; and, in the parallel case of hand-reared 
~~ 
—_ a ee ene 
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