Chap. 33 VERTEBRATES LOWER CHORDATES AND FISHES 679 



Chemical Senses — Taste and Smell. There are organs of taste on the tongues 

 of certain fishes and experiments have indicated that those fishes can taste salt 

 and bitter. Catfishes have taste organs on their whiskerUke barbels and organs 

 of chemical sense are distributed all through their skins. In aquatic animals 

 especially, taste and smell are so similar that it is hard to separate them. The 

 behavior of some fishes does not seem to leave the slightest doubt that they 

 can smell. Sharks have a keen sense of smell, or taste, but when catching its 

 prey a bony fish such as the trout seems to depend entirely upon its eyes. 



Great Migrators. Salmons and eels are true migrators to distant places. 





Fig. 33.14. Long section of the body wall of a fish showing the lateral line 

 sensory system. A branch of the lateral nerve runs to each sensory organ which 

 opens into the minute openings in the body wall and allows water to enter the canal. 

 By means of the lateral line organs fishes taste the water that washes their sides. 

 (Courtesy, Romer: The Vertebrate Body, ed. 2. Philadelphia, W. B. Saunders Co., 

 1955.) 



Under certain conditions in themselves and their surroundings, they journey 

 from their native homes to other places where they live for a time and then 

 in full maturity return to their native waters to spawn. The great migrations of 

 Atlantic salmon have become history. Salmon are now known mainly from the 

 Pacific Ocean and its watershed. They are hatched from the eggs, high up in 

 the rivers away from the sea and spend the first months of their lives there. 

 When they are five or six inches long, in answer to an age-old inherited habit 

 and state of body, they turn downstream. They feed and loiter but finally 

 reach the Pacific Ocean. They remain in the ocean about four years and then 

 as m.ature fishes ready to spawn, they collect near the mouth of a river. The 

 mouth of the Columbia in the state of Washington is a famous gathering place; 

 the mouth of the Fraser in British Columbia is another. The Chinook, blue- 

 back, and silver salmon enter the Columbia in early and late summer and begin 

 their ascent, an army of animals that cannot stop pushing against currents and 

 waterfalls. They swim upstream for hundreds of miles, without taking food, 

 often mounting 19-foot falls, until they reach their native tributary stream. 

 There the female lays her 10,000 or more eggs, the male sheds the milt (sperm 

 cells) over them, and the female covers them with sand. Within a brief time, 

 the exhausted fishes float downstream, dead or dying. The eggs hatch, the 

 young grow, and the story begins over again. 



The change from fresh to salt water demands a period of adjustment. A 

 young salmon can be killed by being dropped into fresh water at the wrong 



