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. Corixae and other small insects should also be given as often as possible. The fresh-water shrimp is bred in running water, Corixae 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 larvae of insects, into the rearing boxes. I have known cases where the larvae 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.