Before leaving this branch of our subject, it is well to consider the geographical distribution of trout dependent as this is upon the character of the water in different sections of the country.

Trout are found in all rivers in which salmon can hatch their young, but as they are not necessarily migratory, they often dwell where salmon cannot. Trout require a temperature of water never exceeding 70°. At 68° they begin to suffer ; at 70°, unless there is a strong and broken current to give life to the water, they die rapidly, and not one will survive a temperature of 75°. It is simply manifest then that the Southern and Western rivers are not generally inhabitable for trout or salmon. Trout may be found in the head waters of such as rise in the Alleghany range of mountains, but salmon can exist in none of them. So also with sluggish, muddy rivers of Ohio, Indiana, Illinois, Missouri, and the vast central region of our continent. Throughout the entire section between the Alleghanies and Lake Superior and the Northern Mississippi, except in Northern Michigan, no trout are found, and then again not till you come to the Rocky Mountains. Trout and salmon, except in the matter of migration, are similar in their habits. The eggs of either may be hatched in the same boxes, with the same water, in about the same time, and under the same treatment. This is being done to-day by the New York Commissioners of Fisheries at the State Hatching House at Caledonia. There are trout, salmo fontinalis, salmon salmo salar, and lake trout salmo-confinis, all being hatched side by side in the same building, in identical troughs and with the same water.

When we speak of the temperature of a pond or river, allowance must be made for springs to which fish will have recourse, precisely as men perishing in a room for air, would put their mouths to a knot-hole to breathe. If there are springs enough, trout will live in waters the body of which reaches a higher temperature than seventy-five. So also, a strong rush of water as with a cataract or rapids, will enable them to endure greater heat than they could otherwise stand. Still it is not safe to subject any of the eastern salmon or trout family to a permanent temperature higher than 65°. Salmon trout suffer most and die the first, at least when they are confined in a limited space with a small flow of water.

The first point in fish culture is to obtain the spawning fish in proper condition, for if the eggs are not mature or ripe, as it is usually called, not only are they useless, but the effort to extract them will kill the parent. Fish breeders who make the cultivation of trout a business, and there are many in this country, keep on hand in suitable ponds a supply of large fish. These are taken from the rivers which they are ascending to spawn, and are kept over from year to year. Connected with the ponds in which they are confined, is a race way, or long narrow trough which has a gravelled bottom, is covered with boards to exclude intrusive eyes, and in every way is made as attractive a nesting spot to the fish as possible. Into this they will proceed of themselves when they are ready to perform their allotted act of reproduction, and the breeder awaiting his opportunity, places a net at the mouth of the race and frightening them in, selects such as are ready for manipulation.

When in a perfectly ripe condition, the eggs lie free in the ovaries in the abdomen, and may be extruded by a gentle pressure downward along the sides of the fish, They are caught in a basin and are vitalized by coming in contact with the milt from the males, for the fish male and female are stripped indiscriminately into one common receptacle. Formerly, the practice obtained of having this basin full of water, under the idea that such arrangement more nearly reproduced the natural conditions, but subsequent discoveries led to a change of this method. The ova are fertilized by the spermatozoa of the milt entering through the micropyle and taking up board and lodging within.

It was ascertained however, in practice, that these spermatozoa, little tadpoles as they appear to be under the microscope, were not fond of water, and although very active when first emitted, soon perished in the water. They retained their vitality much longer when dropped among the ova in a comparatively dry state, and this is the method universally pursued at present. The result of the change was very great; on the earlier plan not more than one egg in three or four was vitalized, whereas now, fully ninety eight per cent. are made capable of producing young as we have already mentioned, and as will be more fully explained hereafter when we come to special and particular directions for each part of the process.

The eggs mature in comparative safety. Some die, of course, others were never properly impregnated, but the percentage is small, not more than five or ten per cent. of the whole. In the natural method probably not one in five hundred, certainly not one in a hundred survives to mature and produce a perfect fish. By the artificial plan, and at the lowest calculation, fully ninety in every hundred are saved and developed. Here is the great gain in fish culture. It is in the primary stages that the advantage is secured. Say that afterwards the perils are alike and still see the enormous difference in its favor. Allow that young fish after their birth are in continued peril of their lives ; that enemies still pursue and waylay, no matter how they are bred; suppose that one-half of all that are born perish before attaining a marketable condition. In one case that half has to be taken from a supply already decimated, in the other nearly the full number is to be drawn upon. Often thousand eggs deposited in the natural method, only twenty or thirty hatch, one-half of these would give us but ten or fifteen full grown salmon, whereas with the care of man nine thousand can be hatched, and it one-half perish we should have remaining four thousand five hundred, a difference so great as to be almost incredible, yet these results are obtained with reasonable certainty by trained fish culturists who understand their business.