Physiological Changes with Age in Fish 203 



The older age groups are represented by so few individuals in 

 the population that it is virtually impossible to collect 

 enough material on which to base critical judgments. 



A thorough review of plaice fecundity has been done 

 recently by Simpson (1951), who added a considerable number 

 of egg counts from the Southern Bight and Flamborough 

 regions of the North Sea. Ovaries were gathered from a total 

 of 256 females taken just before spawning, from mid-October 

 to mid-February, in 1948 and 1949. By inspecting graphs of 

 the fecundity of plaice of similar lengths against age and 

 graphs of fecundity of fish of the same age against length, 

 Simpson was convinced that age, apart from its relation to 

 size, plays an insignificant part in determining fecundity. 



On the chance that statistical analysis might show up dif- 

 ferences that a graphical inspection would not, a covariance 

 analysis of Simpson's 1948 sample from Southern Bight 

 (Table IV) was performed. Ages ranging from II to XVI are 

 represented, although it was necessary to lump together 

 ages II and III and ages XII through XVI in order to have 

 sufficient numbers of observations in the younger and older 

 categories. Regressions of body weight on fecundity at each 

 age were calculated and compared. Simpson had found that 

 fecundity bore a linear relation to weight in plaice, thereby 

 simplifying the computations. The regression coefficients 

 ranged from 0-054 to 0-273 and showed no trends with age. 

 No significant diff'erences were found between the regression 

 coefficients or between the adjusted means. Thus we conclude, 

 as Simpson did, that age has no detectable eff'ect on the 

 fecundity of the plaice. 



Simpson also measured ovary weights and found a rather 

 high correlation between those and egg number (r = 0-890). 

 He provided a complete tabulation of his data, and it was 

 possible to make a more detailed study of this relationship. 

 The Southern Bight information was again used, consist- 

 ing of 163 pairs of observations. Egg number and ovary 

 weights were converted to logarithms and the regression was 



