Fig. 115.—Alaska Blackfish, Dallia pectoralis (Bean). St. Michaels, Alaska.
The Effects of Temperature on Fish.—The limits of distribution of many fishes are marked by changes in temperature. Few marine fishes can endure any sudden or great change in this regard, although fresh-water fishes adapt themselves to the seasons. I have seen the cutlass-fish (Trichiurus) benumbed with cold off the coast of Florida while the temperature was still above the frost-line. Those fishes which are tenacious of life and little sensitive to changes in climate and food are most successfully acclimatized or domesticated. The Chinese carp (Cyprinus carpio) and the Japanese goldfish (Carassius auratus) have been naturalized in almost all temperate and tropical river basins. Within the limits of clear, cold waters most of the salmon and trout are readily transplanted. But some similar fishes (as the grayling) are very sensitive to the least change in conditions. Most of the catfish (Siluridæ) will thrive in almost any fresh waters except those which are very cold.
Fig. 116.—Snake-headed China-fish, Ophiocephalus barca. India. (After Day.)
Transportation of Fishes.—The eggs of species of salmon, placed in ice to retard their development, have been successfully transplanted to great distances. The quinnat-salmon has been thus transferred from California to Australia. It has been found possible to stock rivers and lakes with desirable species, or to restock those in which the fish-supply has been partly destroyed, through the means of artificially impregnated eggs.
The method still followed is said to be the discovery of J. L. Jacobi of Westphalia (about 1760). This process permits the saving of nearly all the eggs produced by the individuals taken. In a condition of nature very many of these eggs would be left unfertilized, or be destroyed by other animals. Fishes are readily kept in captivity in properly constructed aquaria. Unless injured in capture or transportation, there are few species outside the deep seas which cannot adapt themselves to life in a well-constructed aquarium.
Reproduction of Lost Parts.—Fishes have little power to reproduce lost parts. Only the tips of fleshy structures are thus restored after injury. Sometimes a fish in which the tail has been bitten off will survive the injury. The wound will heal, leaving the animal with a truncate body, fin-rays sometimes arising from the scars.
Fig. 117.—Monstrous Goldfish (bred in Japan), Carassius auratus (Linnæus). (After Günther.)