TROUT. THE MANAGEMENT OF THE FRY (_Continued_)
In the last chapter I brought my reader up to the point where the fry,
which had been feeding for some time in the rearing boxes, had been
judiciously separated, the weaker and smaller fish which took up their
positions at the lower ends of the boxes having been put into separate
boxes and induced as much as possible to keep at the head near to where
the current enters.
It is difficult to lay down any certain rule as to what is the best time
at which to take the next step--that of turning the fry out into the
rearing ponds. When the fry have got into more or less regular habits,
and showing no fear of whoever it is who feeds them, come up readily and
seize the food boldly, is probably the best time to let them out into
the larger space of the pond. I do not mean to say that when a certain
proportion of the fish have got over their natural shyness, and feed
boldly and without hesitation, the whole of them should be set free.
What I mean is, that when the habit of associating the appearance of a
certain individual with a meal has been well established among them for
a week or so, they should be allowed to escape from the box into the
pond.
This is best done in the same way that the alevins were allowed to
escape from the hatching tray into the box--by lowering the level of the
box so that its upper edges are some two or three inches below the
surface of the water. The food should now be thrown into the pond higher
up, so that the little fish may be induced to swim up and station
themselves as near the inlet as possible. Probably some of the little
fish will not leave the box at all of their own free will. These, of
course, will have to be turned out. The box should not, however, be
lifted out of the water and the fish and water together be poured out,
as this is very likely to cause them severe injury. The box should be
gradually tilted over and lifted out of the water bottom first, so that
the fish are hardly disturbed at all and certainly not injured in any
way.
An important matter to consider before turning the little fish out into
the pond is, how the ponds are to be protected so that their many
enemies may be kept away from the fry. Kingfishers, herons, and other
creatures are very partial to young trout and will cause enormous
destruction if not prevented. Kingfishers have, in my experience, been
the worst offenders. Some years ago I was rearing some trout in a part
of the country where many of the inhabitants bewailed the extermination
of the kingfisher. Before I began rearing trout I agreed with these
people, for a kingfisher flitting along a stream looking like a little
mass of jewels is a pleasing sight, and one which I had never enjoyed in
that particular part of the country.
When the time came to set my little fish free in the rearing ponds, as a
matter of principle I covered the ponds with herring-net, closely pegged
down on the banks so that I could not even get my hand under the edge. I
did not think that there were any kingfishers or herons about, and so
was very surprised when one morning, on going down to feed the fish, I
found a kingfisher under the net, flying up and down the pond trying to
get out. By carefully introducing a landing-net under the netting over
the pond, I was able to catch the intruder, and caught four more in the
same way in about three weeks. Since that time I have not agreed with
the people who have stated that the kingfisher is almost extinct, at
least in that part of the country. I may say that there are but few
streams there, and that it is not at all an apparently likely place for
kingfishers. I am quite sure that wherever any one begins to rear fish
there he will find that kingfishers are fairly common. The amateur will
probably be also surprised at the way herons appear, if he conducts his
fish-rearing operations, as he should do, in a secluded spot.
Many of the directions I gave as to the management of the fry and the
rearing boxes, apply also to the fry after they have been turned out
into the ponds. The doses of earth should still be given regularly, and
salt may be applied also in the way I have already described. The little
fish will be found to scatter over the pond or to divide again into two
bodies, one at the upper and one at the lower end of the pond, as they
did in the boxes. The fish culturist should try to induce these fish to
come to the head of the pond as much as possible. It is a good thing to
place some boards across the head of the pond to give shade and shelter
to the fry. It will probably be found that if much artificial food is
given to the little fish, a scum will be formed on the surface of the
water. This scum is composed of grease, and should be removed, as soon
as it is observed, with a gauze net.
All the time that these operations have been going on with regard to the
little fish themselves, due attention should have been given to the
vegetation round the ponds. The alders and willows which I before
recommended to be planted round the ponds should be induced as much as
possible to overhang the water. Grass and other vegetation should be
allowed to grow freely round the margins, as many insects are then
likely to fall into the water.
This vegetation will supply the little fish with a certain amount of
natural floating food, without any interference on the part of the fish
culturist; but he should, however, give them other floating food, both
natural and artificial, as much as possible, for this will get them in
their youth to adopt the habit of feeding freely at the surface. When
the alders and willows have grown sufficiently and are well covered with
leaves, they will probably give enough shelter to the fish to make the
boards at the upper end of the pond unnecessary.
As time goes on, and the little fish grow, they should be thinned out,
the smaller and weaker being removed into another pond. Despite the best
endeavours of the fish culturist, a certain number of these small fish
are sure to keep to the lower end of the pond, and it is these which
should be removed first. If they are left, the difference in size
between the smaller and the larger will soon become so great that the
large fish will very likely be tempted to eat the small ones, thus
developing a cannibalistic habit which they will keep always.
At the end of August or the beginning of September the little fish will
have got over the most dangerous part of their lives. After this time
they are called yearlings, are much more hardy and not subject to nearly
as many risks as up to that time.
The great points to remember are:--That the food should be varied as
much as possible; and as much natural food, of a hard description such
as shrimps, _corixæ_, snails, bivalves, etc., be given. That the little
fish should be well protected from enemies. That they should not be
over-crowded, but the weakly and small fish be separated from the larger
fish. That frequent doses of earth should be given to keep the bottom
sweet and clean.[2] That the inlets and outlets should be frequently
cleaned and kept clear, to ensure a good flow of water through the
ponds, and that a careful watch should be kept for such misfortunes as
fungus and dead fish, in order that they may be dealt with at once.
[2] See two letters in Appendix.--Page 93