Physiological Changes with Age in Fish 207 



procedures fail to show any effect of age on the fecundity of 

 either the long rough dab (Hippoglossoides platessoides) or 

 plaice {Pleuronectes platessa). Individual variation in fecundity 

 is very great and masks any effect that age may have. 



Ovary weight and fecundity increase more rapidly in rela- 

 tion to length than does body weight in the long rough dab, 

 haddock, and herring (Clupea harengus and Clupea pallasii). 

 This result strengthens Orton's hypothesis that reproduction 

 becomes an increasing strain on the metabolism of fish as they 

 grow larger and older, thereby causing death either directly or 

 indirectly. 



The number of eggs does not increase in proportion to the 

 weight of the ovary in the haddock, dab, herring, or plaice. 

 Either larger ovaries produce larger and fewer eggs or con- 

 nective tissue increases disproportionately in the ovaries of 

 larger fish. 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. 



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