In a short time, probably within a few days of receiving the ova, the amateur will find that the young fish are beginning to hatch out. They generally come out tail first, and in wriggling this about in their attempts to get further out, they propel the ovum about the bottom of the tray. When the little fish attempts to come out head first, he sometimes gets into difficulties and if this is observed, he may be helped by a gentle touch with a feather or a camel's hair brush. When first hatched out the young fish have a large translucent protuberance on the under-surface. This is the umbilical or yolk-sac, and contains the nourishment upon which the little fish lives during the first stage of its life after it is hatched. This sac is gradually absorbed but until it is absorbed the young fish are called "alevins." At first the little fish do not require any food, but they generally begin to feed in about six weeks, and before the yolk-sac is completely absorbed. The rearing boxes should be kept partly covered, and the alevins will crowd into a pack in the darker parts at the bottom of the hatching tray. The shells of the ova must be removed from the hatching trays. As they are lighter than the alevins, the current will generally carry them to the lower end of the tray, whence they may be removed with a piece of gauze spread on a wire ring, or by raising and lowering the tray gently in the water in alternately slanting directions. The alevin stage is the stage in which the least mortality should be expected, and the little fish give but little trouble. There are, however, several diseases besides fungus (of which I have spoken already when dealing with the ova) from which the alevins may suffer. I was, I believe, the first to describe (in the "Rainbow Trout") a peculiar disease from which alevins suffered. When hatched out and kept in water containing a very large quantity of air in solution, I found that sometimes alevins developed an air bubble in the yolk-sac. On developing this bubble they are unable to stay at the bottom as they usually do, but swim about on their backs at the surface, with part of the yolk-sac out of the water. An effectual cure for this is to put the affected alevins into still water for about thirty-six hours. I have observed this affection in the alevins of the rainbow trout (_Salmo irideus_), the common trout (_S. fario_) and the Quinnat or Californian Salmon (_Onchorynchus conicha_). "Blue Swelling" of the yolk-sac is another disease from which alevins sometimes suffer, but I have never heard of any cure for this. Another, "paralysis," may be caused by lack of sufficient current and by insufficient aeration of the water. Sickly alevins will, as a rule, drop out of the pack, and lie on the bottom or against the end of the hatching tray, where they are carried by the current. Dead alevins should be removed at once, and for this reason it is necessary that the hatching trays should be examined at least once a day.