TROUT. MANAGEMENT OF THE FRY
A greatly varying period of time having elapsed and the yolk-sacs of the
alevins being nearly absorbed, the fish culturist will see that some of
the little fish begin to leave the pack at the bottom of the tray, and
to swim up against the current. When this is observed some very finely
divided food should be offered to these alevins. They will probably dart
at the minute pieces of food floating past and a little more may then be
given to them. If, however, they do not take any notice of little pieces
of food or any other matter which floats past them, they should not be
tried again till the next day. In a few days from the first of the
alevins beginning to feed, all of them will be working up with their
heads to the current, darting at any particles floating in the water.
The tray should now be lowered so that its edge is some three or four
inches below the surface and the little fish allowed to swim out into
the box.
As soon as the yolk-sacs of the alevins are absorbed the little fish
cease to be alevins, and are called "fry."
The alevin stage was that in which the fish give least trouble, the
stage I am now describing is that in which they give most. They must be
fed frequently--at least four times a day. "Little and often" is the
maxim which should rule the actions of the fish culturist with regard to
feeding the fry. If he can only feed his fish four times a day, he must
spend some time on each of these four occasions. The food must not be
thrown in all at once. If this be done the little fish will not get half
of it; the other half will sink to the bottom.
The food should be introduced in small quantities at a time, and if the
amateur has several boxes he should put a little food into each in
succession, coming back to the first when he has put some into the last,
repeating this operation at least half a dozen times. The less he puts
in at each time, and the oftener he does it, the better. The ideal plan
would be to put a very small quantity of food in each time, and to go on
doing this at intervals of from five to ten minutes all day.
Livingstone Stone says, "You need not be afraid of the young fry's
eating too much." And again, "I never knew any healthy young fry of mine
decline eating but once, and then I had fed them incessantly for two
hours, at the end of which time they gave up, beaten." Personally, I
have found no limit to the time that the fry will continue feeding. I
have kept on putting small quantities of food into a rearing box for a
whole afternoon, and I was tired of feeding before the fry were tired of
eating. My reader will infer from this that I believe that the fry
cannot be over-fed, and this is to a certain extent true. If finely
divided food is given in such small quantities that practically none of
it sinks to the bottom without their having a fair chance at it, I
believe that in a box containing only a couple of thousand fry, it would
be found that they never stopped feeding during the whole day. If,
however, too large pieces of food are offered to the little fish, many
of them are likely to be choked and to die, from trying to swallow a
piece a little too big for them.
The amateur will observe that shortly after the fry have been let out
into the box and are feeding freely, they will separate into two more or
less distinct groups. One at the upper end where the current comes in
and is strongest, and one at the lower end. The fish at the upper end
are the strongest and largest. This difference becomes more marked as
time goes on, and in six or eight weeks after they have begun to feed
the larger fish will be almost double the size of the smaller. In the
middle of April, if many fry are in each box, they should be thinned
out, and other boxes brought into use. The smaller fish may then be
taken from one or two boxes and put into another by themselves. In
feeding care should be taken that the small and weakly fish get a fair
share of the food.
No matter how carefully the feeding is managed, some of the food is sure
to escape the young fish and sink to the bottom. This, if left as it is,
will decay and cause great mischief. A very simple and easily applied
remedy for this evil exists in the use of mould dissolved in the water.
Livingstone Stone recommends the mould under a sod, and I have always
used this with the most beneficial effect. Earth, besides covering up
and deodorizing the decomposing food at the bottom, also contains some
materials which are apparently necessary to the well-being of trout. To
quote again from Livingstone Stone, who was the discoverer of this use
of mould: "Earth or mud is the last thing one would suppose suitable for
a fish so associated in our minds with pure, clean water; yet it is an
indispensable constituent in the diet of young trout, and unless they
get it, either naturally or artificially, they will not thrive."
The effect of earth given in this way upon the young fish is simply
marvellous. They become more lively and feed more freely. This is the
effect of a spate--which is, after all, only a dose of earth--upon wild
trout.
The mould should be mixed with water in a bucket, and, when the water is
very thick and muddy, poured into the rearing boxes. The water in the
rearing boxes should be so thick that neither the bottom nor the young
fish, except when they come to the surface to take some passing particle
of food, can be seen. The amateur should not wait till something goes
wrong before giving this dose of earth; it is advisable to give it once
a week at any rate, and oftener if the fish seem to be ailing in any
way.
In dealing with the subject of food for the young fish, I would begin by
impressing upon my reader that the greater variety of food he can give
the better it will be for the fish. He should also give them, at any
rate after they have been feeding some weeks, a certain proportion of
natural food. Probably the best of all food for the fry is pounded
shrimps or other crustaceans. It is, however, difficult in the very
early stages of the trout's life to pound shrimps up small enough, and
the little fish are much given to trying to swallow pieces of food which
are too large for them to manage. This evil proclivity often causes the
death of the fry, and therefore great care must be taken that no pieces
of food which are too large, get into the rearing box. Pounded liver
shaken up in a bottle with water, and after the larger particles have
been allowed to settle at the bottom, poured into the rearing box in
small quantities, is a good form of food for the alevins when they first
begin to feed. The yolks of eggs boiled for about half an hour and
pounded up, dog biscuit very finely pounded, or the fine food supplied
by several of the fish cultural establishments are also excellent. In
giving moist food such as pounded shrimps, liver, meat, or the yolks of
eggs, a good plan while the fry are very small is to put the food in a
small net made of fine muslin mounted on a wire ring, and dipping the
end of this net into the water, allow small particles to escape through
the muslin. This ensures no large pieces getting into the rearing boxes.
As the fry grow larger, these precautions are of course modified, as the
little fish are capable of swallowing larger pieces of food.
With regard to natural food, the amateur should take care to ensure a
good stock for the young fish. Many of the creatures suitable for food
may be cultivated in separate ponds at the same time as the fish, if a
natural supply is not at hand. The _Daphnia pulex_ (water flea) and the
_Cyclops quadricornis_ may be introduced into the boxes very soon after
the fish have began to feed. _Daphnia_ breeds at the rate which is
almost inconceivable. The female produces her first brood of young when
she is ten days old, and goes on breeding at an average of three or four
times a month. The female and her progeny are rendered fertile by one
act of coition, probably for fifteen generations at least, without any
further intervention of the male. Both _Daphnia_ and _Cyclops_ are bred
in stagnant water in which there should be a good stock of weeds.
The fresh water shrimp (_Gammarus pulex_) is an excellent form of food
for young and old trout, and should be given to the fry as soon as they
are old enough to manage them. _Corixæ_ and other small insects should
also be given as often as possible. The fresh-water shrimp is bred in
running water, _Corixæ_ in still or slow running water. Weeds are
necessary to the well-being of both.
The boxes must be kept carefully covered, as I have already pointed out.
A kingfisher would make short work of a box of fry, and other birds and
beasts of various kinds are partial to them. There are only two courses
open to the fish culturist in dealing with these enemies--to protect his
fish or kill the enemies. I prefer to protect the fish first and kill
the enemies afterwards.
The greatest care must be taken not to introduce, or allow to intrude,
any water beetles or the larger carnivorous aquatic larvæ of insects,
into the rearing boxes. I have known cases where the larvæ of the
_Dytiscus marginalis_, the largest of our carnivorous water beetles,
have destroyed almost all the fry in a rearing pond. The adult _D.
marginalis_ itself is not a whit less voracious, and much stronger than
its larva.
If the wooden parts of the apparatus have been properly prepared,
according to my previous instructions, there should be no risk of the
fry developing fungus. Quite a small spot of woodwork, however, left
uncovered by asphalt-varnish, or enamel, or uncharred, will render the
chance of the development of this disease probable.
Should by any misfortune fungus get into the rearing boxes, a dose of
salt may very likely cure it. Sea water is the best, but if this is not
obtainable, a solution of salt and water run through the boxes will
probably cure the disease. Considerable good may also be done to the
young fish by occasionally putting a lump of rock salt in at the inlet,
and the water allowed to run over and dissolve it.