PHYSIOLOGICAL CHANGES 

 ACCOMPANYING AGEING IN FISHES* 



Shelby D. Gerking 



Department of Zoology, Indiana University ^ 

 Bloomiyigton, Indiana 



This paper is a review of efforts that have been made to 

 show the relation between age and two important Ufe func- 

 tions of fishes, nutrition and reproduction. Only a few studies 

 have been made on the effects of age on food conversion, but 

 feeding experiments demonstrate clearly that the ability to 

 convert protein to body flesh declines as size and age increase. 

 Other vertebrates also conform to this pattern, although they 

 achieve a specific size relatively early in life in contrast to the 

 prolonged period of growth in fishes. The rate of decline in the 

 ability to utilize food for growth seems to be a matter of 

 degree, rather than a basic difference between animals of 

 specific and non-specific size. 



Studies of the effect of age on reproduction in fishes have 

 produced no general conclusions. Nevertheless, the subject 

 deserves attention because changes in reproductive capacity 

 with age are commonly used as a criterion of senescence in 

 other vertebrates. The reproductive capacity of live-bearing 

 fishes of the family Poeciliidae declines with age and there 

 may be a period of sterility before death. Neither of these two 

 facts apply unequivocally to egg-laying fishes, however. There 

 is no period of reproductive senility, and it is an open question 

 whether or not age has an effect on reproductive capacity. 

 Individual variation in fecundity is so great that age effects 

 cannot be detected by refined statistical techniques. A more 



* Contribution No. 668 from the Department of Zoology, Indiana Univer- 

 sity, Bloomington, Indiana. 



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