THE AQUATIC VERTEBRATES 1063 



low perch), striped (black bass), or mottled (pickerels, sunfishes, 

 etc.). Large size and strength are the best adaptations against 

 existing fish enemies. Small size and insignificance are advan- 

 tageous for other reasons. Between these, alertness, with power 

 of quick movement, and protective color are the most efficient 

 means of escaping enemies. 



But all of these adaptations are not always sufficient. The 

 most insidious of the fish enemies is the lamprey. So perfect is 

 its means of attachment to its prey, that such a hard-scaled and 

 vigorous fish as Amia caha can rarely prevent the attachment 

 and adhesion, although the most violent efforts be made. If a 

 lamprey is attached to a stone of moderate size, the stone is fre- 

 quently brought out with the fish if the animal is jerked up sud- 

 denly. In letting go its hold all that is necessary is to fill the disc 

 with water from the respiratory bronchus, whereupon suction 

 ceases and the animal is free. In feeding, the sharp teeth pressed 

 against the skin of the animal to which it is attached naturally 

 call the blood to the place. This hyperaemia is caused even more 

 by the suction. At the same time the piston-like tongue with its 

 powerful muscles and the saw-like teeth soon rasp a hole through 

 the skin. The blood is then sucked from the fish and swallowed. 

 The whole operation is something like the extraction of blood by a 

 leech. The lamprey may remain upon a fish so long as the latter 

 supplies sufficient nutriment. Sometimes the fish becomes ex- 

 ceedingly pale and weak so that it floats near the surface. In 

 such a case, the fishermen know immediately that there is a lam- 

 prey attached to the fish, and, with a dip net, usually have no great 

 trouble in catching both. The birds of prey also make this their 

 opportunity and frequently carry off the floating fish, the lamprey 

 sometimes remaining attached until it has been carried a consid- 

 erable distance into the air. 



That the injury to the food fishes is very great may be inferred 

 from the fact that sometimes out of fifteen catfish caught on a set 

 line in one night, ten to twelve have great raw sores where lampreys 

 have attacked them. In the spring, too, when the suckers (Catosto- 

 mus) run up to spawn, very many of them carry a lamprey, and 

 naturally by the great drain of blood it causes, the fish must be 



