FISHKS. 419 



confined to a single region, or to one effort : slioals ot one spe- 

 cies follow those of another through vast tracks of ocean, from 

 the vicinity of the pole, even down to the equator. Thus the 

 cod, from the banks of Newfoundland, pursues the whiting, 

 which llies before it even to the southern shores of Spain. The 

 cachelot is said, in the same manner, to pursue a shoal of her- 

 rings, and to swallow thousands at a gulp. 



This may be one cause of the annual migration of fishes from 

 one part of the ocean to the other; but there are other motives 

 which come in aid of this also. Fishes may be induced to change 

 the place of their residence, for one more suited to their consti- 

 tutions, or more adapted to depositing their spawn. It is re- 

 markable that no fish are fond of very cold waters, and generally 

 frequent those places where it is warmest. Thus, in summer, 

 they are seen in great numbers in the shallows near the shore, 

 where the sun has power to warm the water to the bottom ; on 

 the contrary, in winter, they are found towards the bottom in the 

 deep sea ; for the cold of the atmosphere is not suiTiciently pene- 

 trating to reach them at those great depths. Cold produces the 

 same effect upon fresh-water fishes ; and when they are often 

 seen dead after severe frosts, it is most probable that they have 

 been killed by the severity of the cold, as well as by their being 

 excluded by the ice from air. 



All fish live in the water ; yet they all stand in need of air for 

 tbcir support. Those of the whale kind, indeed, breathe air in 

 the same manner as we do, and come to the surface every two 

 or three minutes to take a fresh inspiration ; but those which 

 continue entirely under water arc yet under a necessity of being 

 supplied with air, or tiiey will exjjirc in a very few mirmtes. We 

 sometimes see all the fish of a pond killed, when the ice every 

 where covers the surface of the water, and thus keeps off the air 

 from the sub-adjacent fluid. If a hole be made in tiic ice, the 

 fish will be seen to come all to that part, in order to take the 

 benefit of a fresh supply. Should a carp, in a large vase of watci, 

 be placed under an air-])iimp, and then be de))rived of its air, 

 during the oj)eration a number of bubbles will be seen standing 

 on the surface of the fish's body ; soon after the animal will ap- 

 pear to breathe swifter, and with greater difficulty ; it will then 

 be seen to rise towards the surface, to get more air-, tiie bubbles 

 on its surface begin to disappear; the l)clly, that was before swollen, 



2p3 



