nty-four hours. _Byssus_
develops only on dead ova.

_Saprolegnia_, known to fish culturists as "fungus," attacks both living
or dead ova. If the woodwork is properly varnished or charred, and the
ova managed thoroughly, there should, however, be but little risk of
fungus. Light is favourable to the growth of fungus, and, therefore,
wooden lids should be placed over the rearing boxes. These should be
kept partially on after the young fish have hatched out, and be replaced
by covers of fine wire netting spread on closely-fitting frames, when
the fry have begun to feed. These obviate the necessity of covering up
the ponds during the first stages.

Many small creatures such as caddis-worms will eat the ova, and
therefore a careful watch should be kept upon the hatching trays as it
is marvellous how such creatures find their way in, in spite of all
precautions. Birds of several kinds are also likely to cause great
damage unless the ova and young fish are carefully guarded from their
depredations.

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 directi