These experiments show the correctness of the opinion expressed by one of the most experienced of writers on the subject of trout culture, Mr. P. D. Malloch, who says in his well-known work on the _Life History and Habits of the Salmon, Sea-trout, Trout and other Fresh-water Fish_[31] (p. 186): “When a farmer rents a piece of land for grazing he knows how many sheep or cattle it will pasture, and that if he puts on more than the proper number they will not grow. He also knows that if he introduce too few they will become fat and too lazy to eat up all the pasture, and he will thus lose part of the money paid for the pasture land. If the proprietor or the tenant of a loch would consider the matter in the same way as the farmer, he would obtain full value out of his lochs, be saved a deal of grumbling, and find life more pleasant.” The same writer also says (p. 157): “Many naturalists maintain that there are different species of trout in the British Islands--Loch Leven trout, Gillaroo trout, tidal trout, and many others--but from a close study of all these trout for the last forty years, I have come to the conclusion that there is only one species of trout in Great Britain, and that in the different varieties the differences are caused by the nature of the water in which they are found and by the food they eat.” Thus, as would be expected, there is no apparent difference between the so-called Loch Leven trout which were put into the loch from the hatcheries and the little trout from my own burns. Numbers of these splendid trout running up to 5, 6, and 7 lb. must be the brothers and sisters of the little fingerlings of the same age in the burns. The best authorities are apparently agreed[32] that the average life of trout is about ten years (although there are authenticated instances in which they have lived for a much longer period), that they reach their prime in six or seven years, that they remain in their prime for a few years longer, and then begin to lose condition and weight as old age creeps on. Those of the trout put into the loch in 1910 and 1911 which I have described as of fair size were about three to the lb., some rather larger and could not then have had many years to live. Those from the burns were probably of different ages, but it is highly likely that in 1913 and 1914, when the yearlings from the hatcheries were put into the loch, there were very few of such other trout as were still there that could live more than three or four years longer.