22 American Fisheries Society 



of its scales undeveloped or so small that no check is registered. 

 Another difficulty arises when the growth for any year is slight, 

 for the checks may come so close together as to be indistinguishable, 

 which is particularly the case in the later years. Unlike so many 

 animals with which we are familiar, the majority of fishes do not 

 reach a definite full size beyond which growth ceases; but under 

 favorable conditions, many continue to grow throughout life, 

 although at a greatly diminished rate when well advanced in 

 years. In these the size attained is limited only by the rate of 

 growth and the duration of life. Carp and pike are reputed to 

 have lived for as long a period as one hundred years, but if the 

 conditions are unfavorable no great size will be attained. It is 

 doubtful whether the age of such long-lived fishes can be deter- 

 mined from the scales, although the annual markings do show that 

 certain fish have lived for at least a quarter of a century. 



When the checks are definitely marked, it is possible from 

 measurements of the distances between successive winter checks to 

 determine the amount of growth in each year of the life of the fish, 

 as has been practised by J. Hjort and other Norwegian investi- 

 gators working with him. Here also it is important to use dis- 

 cretion in our interpretation. We have found that the ratio of 

 the growth of the scale to the growth of the whole fish is a changing 

 one, but by allowing for this a fair approximation to the actual 

 amounts can be made. 



The scales of certain fishes exhibit, in addition to the checks, a 

 varying width for certain, usually concentric, structures known as 

 circuli. The interpretation of the width of these as depending 

 upon the rapidity of growth would indicate that growth is more 

 rapid during the first part of the growing season, which view is 

 confirmed by other methods of investigation. The seasonal 

 growth may be studied by the statistical method, the scale method, 

 or by a combination of the two, as well as by the method of direct 

 observation, when this is practicable. Great differences in seasonal 

 growth have been found. Many of our fishes begin rapid growth 

 in spring or in early summer, but we have found that a certain 

 flat-fish (Hippoglossoides) begins the season's growth in the Bay 

 of Fundy in the winter when the temperature of the water where 

 it lives is still going down. This fish is remarkable because of 

 being able to grow when the temperature is below 32° F. Although 



