Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/693

675 FRESHWATER FISHES.] ICHTHYOLOGY 675 In south-western Australia a mingling of the scanty fauna with that of the southern temperate parts takes place. Oligorus macquariensis (the Murray cod), which has a congener on the coast of New Zealand, ascends htj,h up the Murray river, so that we cannot decide whether this Percoid should be located in the tropical or the temperate part of Australia. Several Gaiaxias also extend to the con fines of Queensland, and will probably some day be found members of this region. In the smaller Pacific islands the freshwater fishes exhibit a remarkable sameness ; they comprise two or three species of Dales, several eels, an atheririe, and some gobies, mul lets, and other fishes which with equal readiness exchange fresh for salt water, and which would at once reach and occupy any streams or freshwater lakes that might be formed on an island. The Sandwich Islands are the only group among the smaller islands which are tenanted by a Siluroid, a species of Arius, which is closely allied to Central American species, and therefore urobably migrated from tropical America. NORTHERN ZONE. The boundaries of the northern zone coincide in the main with the northern limit of the equa torial zone ; but, as has been already indicated, they over lap the latter at three different points. This happens in Syria, as well as east of it, where the mixed faunae of the Jordan and the rivers of Mesopotamia demand the in clusion of this territory in the northern zone as well as in the equatorial ; in the island of Formosa, where a Sal- monoid and several Japanese Cyprinoids flourish ; and in Central America, where a Lepidosteus, a Cyprinoid (Sclero- gnathus meridionalis), and an Amiurus (A. meridionalis) represent the North American fauna in the midst of a host of tropical forms. There is no separate arctic zone for freshwater fishes; ichthyic life becomes extinct towards the pole wherever the fresh water remains frozen throughout the year, or thaws for a few weeks only ; and the few fishes which ex tend into high latitudes, in which lakes are open for two or three months in the year, belong to types in no wise differ ing from those of the more temperate south. The highest latitude at which fishes have been obtained is 82 N. lat., whence the late Arctic Expedition brought back specimens of charr (Salmo arcturus and Salmo naresii). The ichthyological features of this zone are well marked. The Chondrosteous Ganoids or sturgeons, and the families of Salmonidce and Esocidce, are limited to and characteristic of it ; Cyprinoids flourish with the Salmonoids, both families preponderating in numbers over the others, whilst the Siluroids are few in number and in variety. The two regions into which this zone is divided are very closely related to one another, and their affinity is not unlike that which obtains between the sub-regions of the southern zone. Several species are common to both, viz., Acipenser sturio, A. maculatus, Percafluviatilis, Gastrosteus punf/itius, Salmo salar, Esox Indus, Lota vulgaris, Petro- myzon marinus, P. fluvintilis, and P. branchial is ; and all recent investigations have resulted in giving additional evidence of the affinity and not of the diversity of the two regions. In Europe and temperate Asia, as well as in North America, mountain ranges elevated above the line of per petual snow would seem to offer physical conditions favour able for the development of a distinct alpine fauna. But this is not the case, because the difference of climate between the mountain districts and the lowlands is much less in this zone than in the equatorial. Consequently the alpine freshwater fishes do not essentially differ from those &amp;gt;f the plains ; they are principally Salmonoids, and in Asia there are also mountain barbels and loaches. Salmo orientalis was found by Griffith to abound in the tribu taries of the Bamian river at an altitude of about 1 1 000 feet. The Palcearctic or Europe-Asiatic Region. The west ern and southern boundaries of this region coincide with those of the northern zone, so that only those which divide it from North America need to be in dicated. Behring s Strait and the Kamtchatka Sea have been conventionally taken as the boundary, but this is shown to be artificial by the fact that the animals of both coasts, so far as they are known at present, are not sufficiently distinct to be referred to two different regions. As to the freshwater fishes, those of north-western America and of Kamtchatka are but imperfectly known, but there can be little doubt that the same agreement exists between them as is the case -with other classes of animals. The Japanese islands exhibit a decided Palsearctic fish fauna, which includes Barbus and Cobitioids, f .irms strange to the North American fauna. A slight influx of tropical forms is perceived in the south of Japan, where two Bagrina (Psendobagrus aurantiacus and Liocassis longirostris) have established themselves for a considerable .period, for both are peculiar to the island, and have not been found else where. In the east, as well as in the west, the distinction be tween the Europo-Asiatic and the North American regions disappears almost entirely as we advance farther towards the north. Of four species of the genus Salmo known from Iceland, one (S. salar) is common to both regions, two are European (S.fario and S, alpinus), and one is a peculiarly Icelandic race (/S. nivalis). So far as we know the Salmo noids of Greenland and the tract adjoining Baffin s Bay, they are all very closely allied to European species, though they may be distinguished as local races. Finally, as we have seen above, the Europo-Asiatic fauna mingles with African and Indian forms in Syria, Persia, and Afghanistan. Capoeta, a Cyprinoid genus, is charac teristic of this district, and well represented in the Jordan and the rivers of Mesopotomia. Out of the 40 families of freshwater fishes 13 are represented in this region; the number of species is comparatively small, viz., 360. Assuming that the distribution of Cyprinoids has taken its origin from the alpine tract of country dividing the Indian and Palsearctic regions, we find that this type has found in the temperate region as favourable con ditions for its development as in the tropical. Out of the 360 species no less than 215 are Cyprinoids. In the countries and on the plateaus immediately adjoining the Himalayan ranges those mountain forms which we men tioned as peculiar to the Indian Alps abound, and extend for a considerable distance towards the west and east, mixed with other Cyprinina and Cobitidina. The repre sentatives of these two groups are more numerous in Cen tral and Eastern Asia than in Europe and the northern parts of Asia, where the Leuciscina predominate. Abra- midina or breams are more numerous in the south and east of Asia, but they spread to the extreme north-western and northern limits to which the Cyprinoid type readies. The Rhodeina are a small family especially characteristic of the East, but with one or two offshoots in Central Europe. Very significant is the appearance in China of a species of the Catostomina, a group otherwise limited to North America. The Cyprinoids, in their dispersal northwards from the south, are met from the opposite direction by the freshwater Salmonoids. These fishes are, without doubt, one of the youngest families of Teleostei, for they did not appear before the Pliocene era; they flourished at any rateduring the Glacial period, and, as is testified by the survivors which we find in isolated elevated positions, like the trout of the Atl is.