BRITISH FRESH-WATER FISHES 
rearing has perhaps had something, if not a great deal, to 
do with this. A visit to a Trout-farm is a wonderful 
education in fish-culture, and may be strongly recom- 
mended to those who are unacquainted with the various 
stages that are passed through before the perfect little 
fish has celebrated its first yearly birthday. ‘The egg, 
when swollen with water, is about the same size as that 
of the Frog, but the yolk is orange-colour, instead of 
chocolate, and the surrounding substance is greenish- 
yellow, instead of white. 
Careful watch will reveal a perceptible change taking 
place in the centre as the orange yolk darkens, and the 
eyes of the little fish that is in process of development 
soon appear. Later, there are still further changes until, at 
last, the young fry, or alevin as it is called, bursts through 
its covering, with the yolk-sac adhering to its belly as 
shown in Fig. 34. ‘The contents of this latter keep the 
little fellow going for some few days. Meanwhile it is 
experimenting with its swimming capacities, and develop- 
ing in other ways. Once the reserve food is used up, 
however, the perfect alevin has, of necessity, to shift for 
itself. Numerous enemies beset it, but if it survives it 
commences to feed upon various water creatures, such as 
insects, molluscs, and shrimps. But it takes time before 
any perceptible increase of stature is manifest as, at a year 
old, the young Trout has only attained a length of a 
few inches. A year-old Trout is shown life-size in Fig. 
36. Brook, or Burn Trout as they may be called, do 
not grow to any size, indeed many of them are not much 
70 
