208 
Loch Leven trout, and one in three died, the mortality being 
double where the size of the ova of the species from which the 
milt was taken is the larger, thus so far confirming the 
view that the difficulty in fertilisation is partly a mechanical 
one. This brings us to the consideration of whether these 
larger eggs, the produce of older or better fed fishes, will 
eventuate in an augmented size of the offspring, irrespective of 
the question of changing the locality they inhabit, or increasing 
the space or amount of water they reside in. Twosets of Loch 
Leven trout were stripped on the same day in November, 1882, 
the parents of one being six-year-olds, and of the other seven- 
year-olds. The eggs were similarly treated, hatched in the 
same room, during January and February, 1883, and turned 
into two ponds of similar size, each 100 feet long, and fed by 
the same stream. In the upper pond were the progeny of the 
six-year-old; in the lower, which received the stream after 
passing through the upper pond, those from the seven-year-old. 
These ponds we examined on November 29th, 1883, and the 
fry in the upper appeared to average about 2din. in length, and 
in the lower about 3} ins., showing that the offspring from the 
older parents had developed the most satisfactory results. 
Having drawn a net through both ponds and examined those 
captured, it was evident that the averages were much as they 
seemed to be when looking into the water. I selected three of 
the finest fish from each pond, those from the upper averaged 
a little over 3ins., while from the lower they were nearly 4 ins., 
or at nine months of age those which were the progeny of 
seven-year-old parents were nearly a quarter longer than those 
which were descended from six-year-old parents. In March, 
1884, I again visited these ponds, and found the foregoing 
results were being still continued. 
If the eggs of older fish (up to a certain age) give larger 
and quicker growing offspring than do those from younger 
ones, it shows us that fisheries in which only small parents are 
left as stock may not improbably suffer a deterioration in the 
race, and this, irrespective of food, may be one cause of how 
fisheries fall off. 
ee ee ee a ee ee 
atin 
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hed 
