Certainly, as a race, they are not troubled with daintiness; and if they love variety of fare, they can have the same with ease. Pretty much whatever comes in their path is gulped down without hesitation--“gobbled up in the twink of an eye.” Most of them, in cannibalistic style, feed without compunction upon other fishes. While they may be popularly said to “breathe water,” because they take in water instead of air, they depend upon life-sustaining oxygen every whit as much as do land animals, only in a different mode. Large quantities of oxygen are ever present, dissolved, in the sea. It is not the _water_ flowing through the fish’s gills, but the _oxygen_ dissolved in that water, which carries on combustion in the body, and so keeps it in life and health. The amount of oxygen thus obtained is small; therefore the combustion is slow; therefore the blood is cold. But if, for a very short time, all oxygen could be withdrawn from the ocean, the whole multitude of fishes therein would fast die of suffocation. Sea-water alone, without oxygen, could not keep them alive. The gills are, however, so constructed that, while they can use small supplies of oxygen dissolved in water, they cannot use large supplies of oxygen forming part of the free air. So when a fish out of water draws in atmospheric air, its gills become dry and useless, and it dies of suffocation. A world of rapid living and dying is this which we have now in view--of killing and being killed--of an incessant struggle for existence. Many of its inhabitants have no means of defence, save by flight; and these feed only on beings weaker than themselves; largely on the vast hordes of the young of crabs and jelly-fishes. Others are furnished with formidable weapons, wherewith they can actively attack powerful foes. Cold-blooded though they be, and probably without the sense of physical pain, they yet have their little range of emotions. According to one thoughtful and competent observer,[10] they can be frightened, they can be angry, they can endure pangs of jealousy, they can be excited by a spirit of curiosity. And though one may perhaps hardly go so far as to speak of “fishy” affection, shown by one to another, yet some faint reflection of maternal anxiety seems occasionally to exist. [10] ROMANES. They also display a real enjoyment of life, a pleasure in “being,” a delight in playing with water and wave, and even a sportiveness, such as one might imagine to belong only to creatures of a higher grade. On the whole, the brain of a fish is better developed than the brains of any other animals of low rank, excepting only that of the Cuttlefish. Some instances have been known of tame fishes recognising, or seeming to recognise, human beings. It is open to doubt how far the “recognition” meant more than an expectation of something to eat, following upon certain familiar sounds.