The rearing of young salmon and sea-trout is practically the same as that of the common trout, except that they require more water. If kept in rearing ponds they grow more quickly than they do when left to find food for themselves. While young, the salmon is marked with transverse bars of a darker colour than the rest of the body. During the time it bears these marks it is known as a parr.[3] In about fifteen months it loses these marks and becomes quite silvery, being now known as a smolt. Shortly after assuming the smolt dress, the young salmon takes its departure to the sea. In some cases the young salmon do not appear to go down to the sea till over two years after being hatched out, but they should always be set at liberty in March, April, or May in the year following that in which they were hatched out, according to how far they have developed the smolt or silver appearance.
[3] All the trouts go through this stage, which is distinguished by "finger marks" upon the sides.
If spring water is obtainable, particularly if the water, as is usually the case, is of an even temperature throughout the year, the troubles of the fish culturist are considerably lessened. Without a building for the hatching troughs it is almost impossible in many places to guard against frost unless such a spring is available. Sediment may be avoided by putting frames covered with flannel at the inlets to the hatching beds, these will, if kept clean, prevent any sediment from coming into the ponds, and will allow plenty of water to flow in. If hatching trays are not used, the bottom of the artificial bed should be covered with clean gravel.
The time which elapses from the impregnation of the eggs to their hatching out varies according to the temperature of the water, a fairly average time is about ninety days. The ova should be watched during this time, and the dead ones removed. For a short time after they are impregnated they are fairly hardy, but from then till shortly before they hatch out the very slightest concussion will kill or seriously injure them.
The management of sea-trout ova is similar to that of salmon, and the ova are obtained in the same way. As in the case of the salmon it is best to rear the little fish artificially, till they are ready to go down to the sea; they will thus escape dangers likely to cause the loss of about eighty per cent. of their number.
The same methods and the same precautions as advised in the chapters on rearing trout should be adopted in the case of salmon and sea-trout as far as is possible, and if this is done a very large percentage of the ova should be successfully reared to the smolt stage.
CHAPTER XIII
COARSE FISH
Compared to what is known about the early part of the life history of the Salmonidæ, our knowledge of coarse fish is small. Fortunately, however, such lengthy and complicated proceedings as are necessary to obtain a good stock of trout are not necessary to obtain a good stock of coarse fish. If even a few rudd, perch, dace, pike, or carp are put into water where they have a good supply of food to begin with, and which is suitable otherwise for their well-being, the amateur's chief trouble after a few years, if the water is not heavily fished, will be to keep down the stock of coarse fish in proportion to the supply of food.
I have seen many cases where rudd, perch, dace and carp have increased to an enormous extent from a few fish introduced into the water. Some four years ago we put a few small rudd into a mill-pond at home, thinking that the fry they produced would serve admirably as food to the trout which also inhabited the pond. In about twenty months the pond was full of small rudd, and last year we netted out many hundred, as the water was terribly over-stocked with them. The same thing has happened in almost every case which has come to my knowledge; that is, of course, where the waters have been stocked with food, and suitable to the fish introduced.