Huntsman. — The Growth of Fishes 21 



One might have gone further and have given its probable size 

 and perhaps even the name of the lake in which it was caught, as 

 well as other features of its history. It is known that the arrest 

 of growth due to disease or other causes is recorded in the scales. 

 C. K. Gilbert maintains that the salmon from different rivers on 

 the Pacific coast can be distinguished by the peculiar effect of 

 each river on the growth of the salmon in early life as shown in its 

 scales. E. Lea has shown that the herring of the year-class of 

 1904 had a peculiar growth in their third year, in the north of 

 Norway, that made it possible to distinguish them from those 

 of other regions. A certain Atlantic flatfish grows so slowly in 

 the Gulf of St. Lawrence, as compared with the Bay of Fundy, 

 that it was possible for me to correct a dealer as to the source of 

 his fish after an examination of the scales. 



The formation of annual rings or zones in the scales is dependent 

 upon a yearly periodicity in growth. "Warm-blooded" or, more 

 strictly speaking, homoiothermal animals are in large measure 

 independent of outside temperature, for they are able by means 

 of a heat -regulating mechanism to maintain an optimum tem- 

 perature in their bodies. Poikilothermal or "cold-blooded" 

 animals, like plants, vary in temperature with their surroundings, 

 and their activities, including growth, must await a favorable 

 season. In the majority of fishes that have been investigated 

 there is a diminution or arrest of growth during the cold part 

 of the year, and therefore, the age rings on the scales are to be 

 interpreted as "winter checks." 



When these checks can be seen, the determination of the age 

 of a fish is simple enough, but caution must always be exercised. 

 In fishes, such as the salmon, which have a long period of embryonic 

 development including the winter season, it would not be expected 

 that this first winter would be shown on the scales. But, even 

 after hatching, a considerable time must elapse before the scales 

 begin to appear in the skin of the young fish. It is at the time of 

 metamorphosis from the larval or postlarval condition to the final 

 stage, that the scaly coat makes its appearance. Even in the 

 fishes that have a rapid development, such as the saltwater herring, 

 if spawning takes place in the late summer or in autumn, the 

 young fish will remain scaleless during the first winter. Not only 

 so, but a spring-spawning fish may pass the first winter with many 



