There are known at the present about twenty thousand species of fishes, which are distributed throughout the creeks, rivers, lakes, seas and oceans of the world. A few species of the open sea are cosmopolitan; the others are more or less restricted in their range. Northern Asia, Europe and North America have in common a few species of fresh water fishes. There are many others of close relationship, which indicates a somewhat common origin of the fish faunas. The same is largely true of the salt water shore fishes, which live well to the north. The fresh water fishes of South America, Africa and Australia are all different from each other, none being even closely related as are those we find in the countries of the northern hemisphere.

The fishes of our Atlantic coast are different from those of the Pacific, very few species being common to both coasts. The fishes of the Ohio river are entirely different from those of the Columbia, not a single species being common to both streams. The fishes of the Missouri river are very different from the Ohio, many of the larger species, as catfishes, buffalo fishes, black basses, and some of the sun fishes are common to both rivers. The difference between the fishes of these two rivers is chiefly in the smaller kinds, which do not migrate to any great extent, and is greater as you go toward their sources, or confine yourself to their smaller tributaries.

There are many reasons why the fishes of one region are not the same as those we find in another. Some of these reasons we may learn by making a careful study of the fishes of each region, and their environment. In addition we must learn all we can about the past history of the country, finding which streams were formed first, and how they became inhabited from the old ancient fish faunas of our earlier geological periods. If you visit streams in the Alleghanies, the Ozarks and the Black Hills you will find them much alike. All have clear, cool water, flowing over sand or gravel. The black bass, speckled trout, channel cat, and the eastern pickerel will live quite as well in streams of each locality. If you spend a day at each place collecting fishes all your catch will not be the same species. In the Alleghany region you will obtain about forty species, and a like number in the Ozarks. Of these quite one-fourth, or one-fifth, will be the same species, and the others closely related. A large portion will consist of sunfishes and very small, perch-like fishes, which are called darters. These are spiny-rayed fishes; that is, nearly all of the fins are made partly of strong, sharp spines, such as you find on the back of sunfishes, black bass and the like. In the streams of the Black Hills you will not find more than fifteen species, and not more than one or two, if any, will be the same as in either of the other two catches. There are none of the spiny-rayed fishes in the Black Hills, and no trout, though the streams seem in every way well suited for them. The fishes of the Black Hills consist of two catfishes, four suckers, eight minnows, and one member of the cod family. Why are there no spiny-rayed fishes? If you examine a map you will find that the Black Hills is an isolated region, about seventy-five by one hundred miles in extent. It is covered with heavy pine forests and drained by a dozen or more good-sized creeks, which find, through the north and south forks of the Cheyenne, an outlet into the Missouri river. Surrounding the Black Hills is a broad plain one hundred or two hundred miles in width. It has no forests, and only a scant vegetation. Its streams are alkali and contain much solid matter in suspension. None of these streams flow over rocky or gravelly beds. Like all the streams of the great plains they are overloaded with sediment. All the streams can do with this sediment is to deposit it in places during falling or low water, and in time of freshets, pick it up, shift it about and redeposit it farther down the stream. Such streams are like the Platte, narrow and deep in a few places, but mostly wide and shallow, with a bottom of quicksand. The streams of the plains have in them but few species of fishes; especially is this true of the upper Missouri, and these are such species as we find in the Black Hills. It is thus evident that the fishes of this region migrated there, and only such fishes as were able or willing to live in the muddy, alkaline streams of the great plains could have ever reached the Black Hills. The minnows and suckers are ever preyed upon by sunfishes, bass and the like, and to escape them evidently sought retreat in the alkaline water, which was too much disliked by their enemies for them to follow. Once there and accustomed to such water they would migrate farther up stream until they reached the clear, cool streams of the Black Hills. 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 wood-land 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 moraines. 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. Each species of fishes is best fitted for a particular region into which it has been forced to live, either to escape its enemies or to be able to get a living easiest. In its migrations it has moved along lines of least resistance, and has colonized those streams where Mother Nature has been able to do the most for it. The darters are small, perch-like fishes, which seldom exceed a length of six inches, the average being about three. All are active and swift swimmers and well suited for a life among the rocks and swift water of our smaller streams. All countries have small, swift, rocky streams, but few have darters. In their stead we find loaches, gobies, characins, sculpins, and the like. These fishes have "become dwarfed and concentrated, taking the place in their respective habitats which the darters occupy in the waters of the Mississippi valley. By the same process of 'analogous variation' the cichlids of South America parallel the sunfishes of the United States, although in structure and in origin the two groups are diverse."

Dr. Jordan tells us that the trout of the Pacific coast came to America from Asia, and gradually spread eastward and southward until now it is found in all the streams of the Rocky Mountains, the Sierra Nevada, the Cascades and the Coast range. It is but a short distance from Kamchatka to Alaska, and this distance is traveled by trout to this day; once over, a fish able to spend much of its time in salt water could easily colonize all our coast streams. Whether or not all of our Pacific trout are descendants of one species, the cut-throat trout, is more or less uncertain, though it is quite certain that all have descended from not more than two or three species. In many places they have been able to pass from the head waters of one river to that of another, just as they now pass from the head waters of the Columbia to the Missouri by the way of Two Ocean Pass. The ancient lakes, Lahontan and Bonneville, no doubt assisted them in their migrations. Since these have disappeared each colony has had to remain more or less isolated. In time they have become somewhat changed, to better adapt themselves to their new environment. These changes have developed certain peculiar characters, by means of which we can distinguish one kind of trout from another, just as the farmer distinguishes his Berkshire from his Poland China. Spread, as the trout are, over such a large area, in such an immense variety of streams and lakes, and with a vertical range of over one thousand feet, we would certainly expect as large a number of species and varieties of trout to be developed as we find at present in the streams of our west coast.

Fishes are found in the deepest parts of the ocean. Some of these are peculiar to the deep waters, none of the shore fishes resembling them. On the other hand, many deep sea fishes belong to families well represented in the shallow water. The flounders are found in water at all depths, and the same is true of the bat fishes, rock fishes and other shore fishes. It is easy to understand how these fishes have found their way to the deep water. It was either to escape their enemies or to extend their range for some reason; as Mr. Garman puts it, "They have slid down," as it were to the bottom of the ocean.

In general, animals migrating will always move along lines of least resistance. Some deep-sea fishes have a considerable vertical range. It is thought that some move into shallower water to deposit their eggs or place their young in warmer water, and where the peculiar kind of food they need early in life is the most abundant. To study deep sea fishes is difficult, and so little has been done that we not only know them imperfectly but also know very little concerning their life histories.

In February, March and April of 1891 the United States Fish Commission steamer Albatross explored a portion of the region between the coasts of Mexico and Central America and the Galapagos Archipelago. Besides obtaining a large number of shore fishes, about nine hundred specimens of fishes were secured, ranging from a depth of one hundred to twenty-two hundred and twenty-three fathoms. This collection was carefully studied by Professor Garman, of Harvard. He found the collection to contain one hundred and eighty species, eighty-five per cent. of which were new to science. The bottoms of the oceans are far from level, and each deep basin has its own peculiar fauna. The shallower parts of the sea prevent migration of the deep water forms and no doubt living as they do in eternal darkness and in a temperature near the freezing point, there is little to induce them to much activity. The fact that they are easily captured in nets of comparatively small size would indicate that they move about slowly.

Dr. Jenkins, who has lately studied the fishes of the Sandwich Islands, informs me that less than five per cent. are found on our American coast, while a large per cent. is found all the way to the Red sea. In other words, the fishes of the Sandwich Islands are East Indian rather than American. This is no doubt caused from the fact that the deep water between the islands of the American coast forms a barrier which has always prevented the two fish faunas from mingling with each other. Between Africa and the Sandwich Islands this has not been the case. A recent study of the fishes of the Galapagos Archipelago shows its fauna to be American, though in what respect its fishes differ from those of our west coast they resemble all the more the fishes of the Sandwich Islands. Two fish faunas will usually differ from each other if separated by an impassable barrier; especially is this true if the barrier be older than the two faunas.

Any barrier which prevents or hinders fishes in their movements from one body of water to another will separate two more or less well-marked fish faunas. These barriers may be mountains, or shallow water, as in the case of deep sea fishes; deep water, as in case of shore fishes; muddy or alkaline water, or water of different temperature. Temperature no doubt has far more influence in governing the movement of fishes than is generally believed. It plays an important part in guiding salmon up stream to their spawning beds. It explains why they reach the head waters of some streams and spawn earlier than in similar streams not far distant, but of different temperature. If you would know to what extent fishes of one region differ from those of another, study well the barriers between the two regions, learn to what extent and how long they have existed, consider the age geologically of the two regions, and how fishes may have migrated to one or the other, and in a general way you will have the key to the situation, which a careful study of the fishes is quite sure to verify.

Seth E. Meek.