Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/695

677 FRESHWATER FISHES.] ICHTHYOLOGY G77 the analogue of Salmo, and Prototroctes that of Coregonvs), and the Galajciidce, which are the pikes of the southern hemisphere. Although geographically widely separate from each other, the freshwater fishes of the three divisions are nevertheless so closely allied that conclusions drawn from this group of animils alone would hardly justify us in regarding these divisions as sub-regions. One species of Galaxias (G. at- teiiuatus) and three of lampreys are found in all three, or at least in two of the sub regions. Percichthys is in Chili the ( autochthonous form of the cosmopolitan group of Percina. Diplomi/sfax, an Arioid fish of Chili, and Nematogenys seem to have crossed the Andes from tropical America at a comparatively early period, as these genera are not repre sented on the eastern side of South America ; Trichomyc- teriua occur on both sides of the Andes, which they ascend to a considerable height. Retropinna is a true Salmonoid, allied to the northern smelt (Osmerus), and representing it in the southern hemisphere. In both these genera part of the specimens live in the sea, and ascend rivers periodically to spawn ; another part remain in rivers and lakes, where they propagate, never descending to the sea, this freshwater race being constantly smaller than their marine brethren. That this small Teleostean of the northern hemisphere should reappear, though in a generically modified form, in New Zealand, without having spread over other parts of tli3 southern zone, is one of the most remarkable and at present inexplicable facts of the geographical distribution of freshwater fishes. BRACKISH-WATER FISHES. On those parts of a coast at which there is a mixture of fresh and salt water, either in consequence of some river emptying itself into the sea, or from accumulations on the lind-surface forming lagoons which are in uninter rupted or temporary communication with the sea, there flourishes a peculiar brackish-water fauna characterized by the presence of fishes found sometimes in the sea, and sometimes in pure fresh water. This fauna can be somewhat sharply defined if a limited district only is taken into consideration : thus, the species of the brackish-water fauna of Great Britain, of the Pacific coist of Central America, of the larger East India islands, &amp;lt;fec., can be enumerated without much hesitation. But difficulties occur when we attempt to generalize in the enumeration of the forms referable to the brackish-water fauna, because the genera and families enumerated include curtain species and genera which have habituated them- solves exclusively either to a freshwater or a marine exist ence, and also because a species of fish may be at one locality an inhabitant of brackish water, at another of the sea, and at a third of fresh water. The circumstance that these fishes can live either in the sea or in fresh water has enabled them to spread readily over the globe, a few only being limited to particular regions ; in dividing the earth s surface into natural zoological regions, therefore, the t-ixonomist receives no assistance from the brackish-water i &amp;gt;rni3. The following fishes may be referred to this fauna : 1. Species of Raiidcc (Raia, Trygon). 2. Ambassis. 3. Thcraprm. 4. Numerous Scmnidcv of the equatorial zone. 5. Pofyncmidtc. 6. Numerous species of Caranjc (or horse mackerels) of the equatorial eoiie. 7. Species of Gastrosteus. 8. The most important genera of the gobies (Gobiina) ; Gobius (nearly cosmopolitan), Sicydium, Boleophthnlmus, Pcriophlhalmiis, Elcotrls (equatorial). 9. Ambhjo- pina. 10. Trypauchenina. 11. Many species of Blcnnius. 12. The majority of Athrrinidce. 13. Most Muyilidn. 14. Many Pleura- ncdid/e. 15. Several Siluridae, as especially the genera Plotosus, Ciiidoglanis, Arius. 16. Many Cyprinodontidcc. 17. Species of Clupea. 18. Chatoessus. 19. Mvjalops. 20. Anguilla (eels). 21. Numerous SynqnathicUe. This list could be considerably increased if an enume ration of species, especially of certain localities, were at tempted ; but this is more a subject of local interest, and would carry us beyond the scope of a general account of the distribution of fishes. MARINE FISHES. Marine fishes fall, with regard to their mode of life and distribution, into three distinct categories: 1. Shore Fishes that is, fishes which chiefly inhabit parts of the sea in the immediate neighbourhood of land either actually raised above, or at least but little submerged below, the surface of the water. They do not descend to any great depth, very few to 300 fathoms, and the majority live close to the surface, The distribution of these fishes is determined, not only by the temperature of the surface water, but also by the nature of the adjacent land and its animal and vegetable products, some being confined to flat coasts with soft or sandy bottoms, others to rocky and fissured coasts, others to living coral formations. If it were not for the frequent mechanical and involuntary removals to which these fishes are exposed, their distribution within certain limits, as it no doubt originally existed, would resemble still more that of freshwater fishes than we find it actually does at the present period. 2. Pelagic Fishes- that is, fishes which inhabit the surface and uppermost strata of the open ocean, and approach the shores only accidentally, or occasionally (in search of prey), or periodically (for the purpose of spawn ing). The majority spawn in the opan sea, their ova and young being always found at a great distance from the shore. With regard to their distribution, they are still subject to the influences of light and the temperature of the surface water ; but they are independent of the variable local con ditions which tie the shore fish to its original home, and therefore roam freely over a space which would take a freshwater or shore fish thousands of years to cover in its gradual dispersal. Such as are devoid of rapidity of motion are dispersed over similarly large areas by the oceanic cur rents, more slowly than the strong swimmers, but not less surely. An accurate definition, therefore, of their dis tribution within certain areas equivalent to the terrestrial regions is much less feasible than in the case of shore fishes. 3. Deep-Sea Fishes that is, fishes which inhabit such depths of the ocean that they are but little or not at all influenced by light or the surface temperature, and which, by their organization, are prevented from reaching the sur face stratum in a healthy condition. Living almost under identical tellurian conditions, the same type, the same species, may inhabit an abyssal depth under the equator as well as one near the arctic or antarctic circle ; and all that we know of these fishes points to the conclusion that no separate horizontal regions can be distinguished in the abyssal fauna, and that no division into bathymetrical strata can be attempted on the base of generic much less of family characters. Chondroptcrygii, Acanthopt&amp;lt;ry&amp;lt;jii, Anacanths, Myxi- noids, and Pharynffobranchii furnish the principal contin gents to the marine fauna ; whilst the majority of Physo- stomes, the Ganoids, and Cyclostomes are freshwater fishes, Shore Fishes. The principal types of shore fishes are the following : CuoNDROPTERYrm. Holoccphcda, 4 species. Plagiostomata Carchitriidifi(part), 12; Seylliidie, 30 ; Cestraeiontidre, 4 ; Spinacida (part), 8 ; Khinida?, 1 ; Pristiophoridse, 4 ; Pristidie, 5 ; Rhiiiobatidse r 14 ; Torpedinidiu, 15 ; Raiidre, 34 ; Trygonidie, 47. ACANTHOPTEBYGII. Percidie (part, includ. Pri.stipomatidie), 625