Government agencies that are striving to maintain the fish supply. The present report is a revised and amplified edition of the one published by theB ureau ofF isheries in 1915. The exhaustion of the supply of that document and the continued public demand for information on this subject, together with the availability of new data on the fishes, make this publication desirable. INDIGENOUS FISHES. The native fish life of the park was profoundly affected by the great lava flow which occurred over a large part of the park in Pliocene times. Whatever fishes were then present were necessarily killed, and, with the reestablishment of the watercourses after the cooling of the surface of the lava, fishes in outside waters were to a great extent prevented from reaching the lofty plateau, which comprises most of the area of the park, by the high and steep falls over which the streams leave the lava beds. It thus follows that the native fish fauna of the park is very limited. Except in Yellowstone River and its tributaries practically no fishes occur naturally above the falls, and in the extensive basin of that river the few species that do exist gained access to the region above the falls because of the imperfect watershed separating theY ellowstone and theS nakeR iver basins. The original comparative barrenness of the park in fish life was due entirely to topographical conditions. The physical character of the waters is, in general, highly favorable for fishes, and an examination of the streams and lakes of the park by Prof. Forbes in 1890 disclosed the presence in certain barren waters of an abundant insect and crustacean food well suited for sustaining certain kinds of fishes. The theory that would account for the original absence of fishes in particular park waters as due to the high temperature and chemical constituents of the great volumes of water flowing from t (Typographical errors above are due to OCR software and don"t occur in the book.)