If we compare the fishes of two rivers whose mouths are near each other, as the Ohio and the Missouri, those fishes found near the mouths will be the same species and the two river faunas will differ most as you go toward, their sources. On the other hand, if you select two rivers whose sources are near each other, as the James and tributaries of the Ohio, then the fish faunas will differ most as you go towards their mouths. The same is true of the Missouri and, the Columbia. In such cases it often happens that during high water some fishes are able to pass from the head waters of one river basin to the other, just as we see the trout from the Columbia at the present time colonizing the upper Yellowstone through the Two Ocean Pass.

Near the head waters of many mountain streams there is usually a pass, which contains a strip of meadow land where the small streams from mountains unite, forming the sources of two great rivers flowing in opposite directions. This is the case both at the. Two Ocean Pass, the source of the Missouri and the Columbia, and at the point where the Canadian Pacific Railroad crosses the divide, forming the source of the Frazier and Saskatchewan rivers. Many mountain streams whose sources are at present in no way connected may have been so at no very remote period. All of our streams, which have their sources within the glaciated area were no doubt connected as the ice receded. The drainage of Lake Champlain and the lakes in central New York was southward at the close of the glacial epoch. It is said that in times of high water one may pass in a skiff from the head waters of the Mississippi to the Red River of the North.

With such facts before us we can easily understand why the fishes of two rivers whose sources are near each other should be most nearly alike nearest the divide. If the two rivers were formed about the same time, as no doubt were the James and the Ohio, they would naturally have several species in common. In other words, the two fish faunas will resemble each other throughout their whole extent. In the case of the Missouri and the Columbia, the former is much the older stream, and while their sources have fishes common to both streams, in the lower parts of the rivers the fish faunas are entirely different.

The upper Missouri river and its tributaries are for the most part inhabited by Rocky Mountain fishes, practically the same fauna as we find in the Columbia, but few species characteristic of the Mississippi valley have been able to even cross, the great plains and none have ever passed the Rocky Mountain divide.

In the study of the geographical distribution of our fresh water fishes, we are able to make a few generalizations as follows: Two rivers in the same latitude, and belonging to the same great drainage basin, and draining similar areas,, will have similar fish faunas. Thus we find a great similarity in the fishes of the Washita and the Tennessee rivers, a much greater similarity than we do in the fishes of the Washita and the Cedar rivers. If the stream is a large one, the fishes near its source will be much unlike those near its mouth. The fishes of Minnesota differ greatly from those of Louisiana, though the drainage of these two States is in the Mississippi river basin. Limestone streams have in them more species of fishes than do sandstone. All things being equal, the larger of two or more streams will contain the most species of fishes. There are few, if any, rivers as rich in species as the Mississippi river and its tributaries. It drains one slope of each of our two great mountain systems, besides an immense area of woodland and prairie, and numerous swamps and marshes. Its upper course and many of its upper tributaries lie in the region once covered by glaciers, though now traversed by great morains. Its fishes are as diversified as the area it drains. In its mountain streams we find such fishes as the trout., darters, minnows and suckers. In the upland streams are darters, shiners, suckers, sunfishes and small-mouthed black bass.

In the channels of the larger tributaries are found the large suckers, buffalo fishes, gar pike, channel catfish, drum, pike and pickerel. The lowland streams contain the dogfish, pirate perch, some sunfishes, the large-mouthed black bass, some suckers, catfishes and other species. Minnows, darters, suckers and sunfishes are found in lowland, upland and mountain streams, though not the same species in each. These fishes belong to families which are made up of many species, some being strictly upland, others strictly lowland, each having a limited range. In the same way we have fresh water fishes and salt water fishes; some fishes, as the trout and salmon and eel, live in both salt and fresh water. Many other fishes, as the killifishes, thrive best in brackish water.