Page:British Reptiles, Amphibians, and Fresh-water Fishes.djvu/86

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 recommended 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 developing 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