394 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



1944 



1945 



1946 



1947 



1948 1949 



YEAR 



1950 



1951 



1952 



1953 1954 



Figure 15. — Annual fluctuations in the growth in length of Saginaw Bay yellow perch in the second and later years 

 of life. Males, broken line ; females, solid line ; both sexes, dots and dashes. 



cent) whereas that in later years of life was at 

 the maximum (16.8 percent). Other calendar 

 years show similar disagreements; furthermore, 

 the trends were entirely different (cf. figs. 14 

 and 15). 



Growth in Weight 



Growth in weight of the age groups: general growth 



Data on calculated growth in weight (tables 

 36 and 37) were obtained by applying the calcu- 

 lated lengths of tables 26 and 27 to the length- 

 weight equation. Thus the length and weight 

 at a particular age derived by this equation are 

 exactly comparable. (The mean weight of a 

 group of fish in which both length and weight 

 vary is higher than the normal weight of a fish 

 of average length.) 



The discrepancies among the calculated weights 



of the different age groups are so similar to those 

 previously described for the calculated lengths 

 that they may be summarized briefly and with very 

 little comment. Among the males and in age 

 groups III-VI of the females growth rate gener- 

 ally decreased with increase of age. The dis- 

 crepancies were small in the earlier years of life, 

 but became larger with increase in the year of 

 life for which the calculations were made. In 

 age-groups VII-IX of the females this down- 

 ward trend of growth rate was reversed and 

 growth in weight was relatively fast. The pre- 

 vious discussion of factors of discrepancies in 

 calculated lengths applies, of course, to the cal- 

 culated growth in weight. 



With growth in weight as with growth in 

 length, the general growth (table 38; fig. 16) is 

 based on the sums of the grand average incre- 



Table 36. — Calculated weights at the end of the different years of life for male yellow perch collected during the spawning season 



of 1943-55 

 [Increments in parentheses) 



