ACCLIMATIZATION.] ICHTHYOLOGY 665 cliraa- ition. . >reg- i ion of Attempts to acclimatize particularly useful species in countries in which they are not indigenous have been made from time to time, but have been permanently successful in a few instances only, the failures being due partly to the choice of a species which did not yield the profitable return expected, partly to utter disregard of the difference of climatic and other physical conditions between the original and the new homes of the fish. The first success ful attempts at acclimatization were made with domestic species, viz., the carp and goldfish, which were transferred from Eastern Asia to Europe. Then, in the early part of the present century, the Javanese goramy was acclimatized in Mauritius and Guiana, but no care seems to have been taken to insure permanent advantages from the successful execution of the experiment. In these cases fully developed individuals were transported to the country in which they were to be acclimatized. The most successful attempt of recent years is the acclimatization of the trout and sea-trout, and probably also -of the salmon, in Tasmania and New Zealand, and of the Californian salmon (Salmo quinnat .?), in Victoria, by means of artificially-impregnated ova. In transporting these ice was employed, in order to retard their development generally, and thus to preserve them from destruction during the passage across the tropical zone, ificial Artificial impregnation of fish-ova was first practised by J. L. Jacobi, a native of Westphalia, in the years 1757-63, who employed exactly the same method which is followed now ; and there is no doubt that this able observer of nature conceived and carried out his idea with the distinct object of advantageously restocking water-courses that had become unproductive, and increasing production by fecundating and preserving all ova which, in the ordinary course of propagation, would be left unfecundated or might accidentally perish. Physiology soon turned to account Jacobi s discovery, and artificial impregnation has proved to be one of the greatest helps to the student of embryology. Fishes differ in an extraordinary degree with regard to tenacity of life. Some will bear suspension of respiration caused by removal from water, or by exposure to cold or heat for a long time, whilst others succumb at once. Nearly all marine fishes are very sensitive to changes in the temperature of the water, and will not bear transporta tion from one climate to another. This seems to be much less the case with some freshwater fishes of the temperate zones ; the carp may survive after being frozen in a solid block of ice, and will thrive in the warmest parts of the temperate zones. On the other hand, some freshwater fishes are s) sensitive to a change in the water that they perish when transplanted from their native river into another apparently offering the same physical conditions (gray ling, tialmo hncho). Some marine fishes may be trans ferred at once from salt into fresh water, like sticklebacks, some blennies, and Coitus, &c. ; others survive the change when gradually effected, as many migratory fishes ; whilst others, again, cannot bear the least alteration in the composition of the salt water (all pelagic fishes). On the whole, instances of marine fishes voluntarily entering brackish or fresh water are very numerous, whilst fresh- A-ater fishes proper but rarely descend into salt water. Abstinence from food affects different fishes in a similarly different degree. Marine fishes are less able to endure hun ger than freshwater fishes, at least in the temperate zones, no observations having been made in this respect on tropical fishes. Goldfishes, carps, and eels are known to be able to subsist without food for months, without showing a visible decrease in bulk ; whilst the Trigloids, Sparoids, and other marine fishes survive abstinence from food for a few days only. In freshwater fishes the temperature of the water has great influence on their vital functions generally, and .acity ( ife. consequently on their appetite. Many cease to feed alto gether in the course of the winter ; a few, like the pike, are less inclined to feed during the heat of the summer than when the temperature is lowered. Captivity is easily borne by most fishes, and the appliances Captivit introduced in modern aquaria have rendered it possible to keep in confinement fishes which formerly were con sidered to be intolerant of captivity, and even to induce them to propagate. Wounds affect fishes generally much less than higher Injury vertebrates. A Greenland shark continues to feed though from its head is pierced by a harpoon or by the knife, so long woun(l8 - as the nervous centre is not touched ; a pike will survive the loss of its tail, or a sea-perch that of a portion of it, and a carp that of half its snout. Some fishes, however, are much more sensitive, and perish even from the super ficial abrasion caused by the meshes of the net during capture (Mullus). The power of reproduction of lost parts in Teleosteous feepro- fishes is limited to the delicate terminations of their fin-rays Auction and the various tegumentary filaments with which some are provided. These filaments are sometimes developed in an extraordinary degree, imitating the waving fronds of the seaweed in which the fish hides. The ends of the fin- rays and also the filaments are frequently lost, not only by accident, but also merely by wear and tear ; and, as these organs are essential for the preservation of the fish, their reproduction is necessary. In Dipnoi, Ceratodus, and Pro- topterus, the terminal portion of the tail has been found to have been reproduced, but without the notochord. Hibernation has been observed in many Cyprinoids and Hiberna Muroenoids of the temperate zones. They do not fall into t * on * a condition of complete torpidity, as reptiles and mammals do, but their vital functions are simply lowered, and they hida in sheltered holes, and cease to go abroad in search of their food. Between the tropics a great number of fishes (especi ally Siluroids, Labyrinthid, Ophiocephaloids, the Dipnoi) are known to survive long-continued droughts by passing the dry season in a perfectly torpid state, imbedded in the hardened mud. Protopterus, and probably many of the other fishes mentioned, prepare for themselves a cavity large enough to hold them, and coated on the inside with a layer of hardened mucus, which preserves them from complete desiccation.. It has been stated that in India fishes may survive in this condition for more than one season, and that ponds, known to have been dry for several years and to a depth of many feet, have swarmed with fishes as soon as the accumulation of water released them from their hardened bed. The principal benefit derived by man from the class of Ecouo fishes consists in the abundance of wholesome and nourish- ^cuses ing food which they yield. In the polar regions especially, whole tribes are entirely dependent on this class for subsistence ; and in almost all nations fishes form a more or less essential part of food, many, in -a preserved con dition, being most important articles of trade. Their use in other respects is of but secondary importance. Cod- liver oil is prepared from the liver of some of the Gadoids of the northern hemisphere and of sharks, isinglass from the swim-bladder of sturgeons, Scisenoids, and Polynemoids, and shagreen from the skin of sharks and rays. The flesh of some fishes is constantly or occasionally Poisoii- poisonous. When eaten, it causes symptoms of more or us less intense irritation in the stomach and intestines, inflam- mation of the mucous membranes, and not rarely death. The fishes which appear always to have poisonous proper ties are Clupea thrissa, Clupea venenosa, and some species of Scants, Tetrodon, and Diodon. There are many others which have occasionally or frequently caused symp toms of poisoning, Poey enumerates no less than seventy-
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