Page:Natural History, Fishes.djvu/43

Rh exists among the races, and the indefatigable assaults committed by man upon them, it is probable that the actual average of life among Fishes is of comparatively short duration.

Tenacity of life must be distinguished from its durability. In this property much difference is found amongst fishes. Mr. Yarrell observes that those species which swim near the surface of the water, have a high standard of respiration, a low degree of muscular irritability, great necessity for oxygen, die soon—almost immediately on being taken out of the water—and have flesh prone to rapid decomposition; of these, Mackerel, Salmon, Trout, and Herrings are examples. On the contrary, those that live near the bottom have a low standard of respiration, a high degree of muscular irritability, and less necessity for oxygen: these sustain life long after they are taken out of the water, and their flesh remains good for several days: Carp, Tench, Eels, the different sorts of Skate, and all the Flat-fishes are examples of this class. Some species, as the Eels and the Ophiocephali, continue to exhibit vigorous tokens of life, under inflictions that would be fatal to most other animals; the removal of the skin, and even the division of the body into pieces, not immediately producing death.

The power of sustaining extremes of temperature, found in this Class of animals, may perhaps be considered an indication of their low place in the scale of organization. Broussonet found, by experiments, that several species of freshwater Fishes lived many days in water so hot that the hand could not be held in it a single