- 
that more than others will be likel 
890 Transactions. 
DETERIORATION. 
Regarding the growth of trout in the mountain-lakes of eastern Norway 
in comparison with the degenerate condition of trout on the western side, 
Dahl (1919, p. 28) notes as follows :— 
—— West. | East. 
Food .. | Mostly insects and small organisms | Mostly large animals, fresh-water 
shrimps, snails, and Lepidurus. 
Lakes  .. | Often deep, and therefore little | Often shallow, and therefore more 
productive productive. 
Spawners.. | Small and young, therefore vigorous | Larger and older, therefore slower 
reproduction reproduction. i 
Ova -. | Small, with small growth-capacity | Large, with better growth-capacity. 
Dahl’s researches are of great interest and importance ; but much further 
investigation seems to requiréd before these reasons and results may 
be accepted in their entirety. 
istead (1920, p. 58) states as follows: “ A stock of mountain-trout 
subjected to a favourable environment may grow and improve for some 
years. ter a time a recoi es place and the improvement is replaced 
by a deterioration, apart, as far as I can tell, from the question of food. 
It is as though the vitality accumulated originally through generations of 
hardship was exhausted in the process of growth.” 
Dahl (1919, p. 33) states that “ growth depends on the qualities of the 
vigour imparted by the parents to their progeny. 
here can be no doubt that decreasing food-supply has a direct bearing 
on the question in the thermal lakes, but I am of the opinion that this is 
not the solution of the whole problem. 
regard to Dahl’s tabulated ‘observations, it would be interesting to 
ascertain whether outside fry or young trout were introduced into any of 
the lakes to augment the parent stock; also whether the trout of the 
eastern lakes of Norway had greater natural facilities for sexual inter- 
mixing than was afforded the trout on the western side. Further, it may 
these large trout (which at the age of six years weigh anything up to 9 lb.) 
ar : li to. produce a strong and healthy 
progeny, and thus aid in maintaining the basic standard of the race. 
Progeny derived from the same parents may not impress upon their 
progeny a strong constitutional vigour. Milne (1917, p. 37) writes: “ It 
ote See noticed that if eggs are collected annually to the full capacity of 
à minor tributary in a large watershed, and some of the progeny are 
* Phillipps and Grigg (1922) have gi ide | s : 
and inorganic geochemistry to in м oom considerable data on the relations of organic 
