Page:Popular Science Monthly Volume 47.djvu/768

750 pounds weight prefers something more substantial, like a yearling trout or two for breakfast and a few more at intervals, with flies and worms for dessert; and this cannibalism is what keeps the balance of life in a natural state. If, however, it is decided to follow the first-named system, it will only be necessary to provide spawning races for the adults and follow the rules for hatching the eggs, and either turn out the product as fry or as yearlings; the latter will give the best results where transportation is not needed, as in the work of the fish commissions of the different States.

Where it is desired to make a business of trout-raising a series of small ponds are necessary. After leaving the springs the water, in summer, is continually approaching the temperature of the air; and when it gets to 70° the danger line is reached. In swift water our brook trout have lived at five degrees above that point, but they suffered, and some have died, while others lived until the declining sun permitted the water to cool a trifle. This is a point that should be in mind when planning ponds, for it is of the greatest importance. A spring brook that will sustain many trout in a pond of half an acre might fail to keep a single one if the area was doubled. The surface and the shallows are warmer in summer than the deeper portions, and in the case of springs in the bottom of lakes or ponds the trout will gather about them in warm weather. In the pond system the ponds are so small that the fish can be seen at all times and their growth noted, so that those which have outstripped their fellows may be taken out and placed with others of the same size. This is practiced once a year with the larger fish and about three times during summer with the "babies," or those not yet arrived at the dignity of yearlings. Cannibalism is not only prevented by this, but the smaller ones will have a chance to get food at the first table, from which they have been debarred.

Perhaps a description of the ponds that I have made for the Fishery Commission of the State of New York at Cold Spring Harbor, Long Island, may best illustrate the idea of small ponds, first explaining that the object of the ponds is not only to grow trout, but to get the greatest amount of eggs for hatching in order to stock public waters with the different species of trout, such as