182 Shelby D. Gerking 



subtle change in the ovary has been discovered that has not 

 been appreciated before, however. Egg number does not 

 increase in proportion to ovary weight. Either eggs become 

 larger and fewer or the relative amount of connective tissue 

 increases as the ovary grows. No critical evidence is available 

 to support either contention. If the latter is true, ageing 

 changes in the gonads of fishes would be similar to those in 

 higher vertebrates. The lack of conclusive proof of the effect 

 of age on reproduction is disturbing because it has not been 

 possible to accept or refute without question that portion of 

 Bidder's argument (1925a) that fish are immortal because old 

 individuals show no decline in reproductive capacity. 



Knowledge about fishes has not progressed to the point 

 w^here the relative importance of the influence of rate of 

 growth and chronological age on physiological function can 

 be distinguished. This constitutes a great w^eakness in the 

 analysis of differences in nutrition and reproduction related 

 to size and age. Svardson (1951) has expressed the opinion 

 that age of fishes should be expressed as "physiological age" 

 based on nutrition and rate of growth. Larkin, Terpenning 

 and Parker (1957) have demonstrated that growth of rainbow 

 trout {Salmo gairdneri) in different British Columbia lakes can 

 be dealt with more effectively by comparing growth rates of 

 fish of the same size rather than of the same age. This point 

 of view reflects a tendency to depart from traditional age and 

 growth studies because of dissatisfaction wdth chronological 

 age as an adequate unit on which to base physiological change. 

 Critical experiments are clearly needed to separate the effects 

 of rate of growth from those of chronological age. In view of 

 the lack of information it has been necessary to refer in the 

 ensuing discussion to age and size indiscriminately without 

 distinguishing which of the tw^o factors is the more important. 



Efficiency of Protein Utilization for Growth 



A series of studies on the protein metabolism of sunfish, 

 family Centrarchidae, has been done in order to learn whether 



