EGGS AND ALEYINS 79 



It is easy enough to assign such loss as must occur in nature to its 

 various causes. Amongst these must be reckoned original want of 

 fertilisation of a proportion of the ova shed and the immediate 

 devouring of some of it by predatory fish in attendance on the spawners. 

 Then the vicissitudes of the weather must be reckoned with, for an 

 excessive drought may lay bare the shingle in which the eggs are 

 deposited and exceptional floods may sweep the gravel beds wholly 

 away. Then there is a host of creatures — larvae, beetles, fish, and 

 birds — which levy a constant toll upon the eggs and alevins. Finally, 

 it has been discovered through hatchery work that a heavy death-rate 

 occurs amongst the alevins, due perhaps, as it has been said, to an 

 inflammation of the gills at the stage when the umbilical sac has become 

 almost absorbed and the little fry begin to forage for food. I have 

 suggested elsewhere that probably this particular mortality is increased 

 by artificial rearing, especially where hand feeding is resorted to. But 

 in any case it requires no great stretch of the imagination to assume a 

 considerable mortality at this critical transitional period even with fish 

 in their natural environment. 



All that human ingenuity can do to mitigate loss, without resorting 

 to hatchery operations, is to secure that as large a stock as possible of 

 healthy fish deposit their spawn in peace, and that the eggs and alevins 

 are protected as far as may be from predatory enemies. 



It is hardly worth while to quote such estimates as have been made 

 of the wastage that occurs, but Dr. Francis Ward, in his " Marvels of 

 Fish Life," remarks that " in nature only a small percentage of the eggs 

 deposited result in the birth of an alevin." If this is so, how few of the 

 eggs hatched must produce a fish destined to reach maturity. Yet the 

 numbers of sea-trout, in some seasons, are in fact enormous. 



I have postponed till later consideration of the actual process of 

 spawning and the periods of spawning, but, to summarise here what is 

 contained in the foregoing pages, we may assume the sea-trout ova to 



