Physiological Changes with Age in Fish 191 



Bidder's theory that fish are potentially immortal has never 

 attracted much attention among fishery workers. No doubt 

 its lack of popularity is due to the fact that those who work 

 with fish know that they die and that the lifespan of most 

 species is short compared with our own. Among the host of 

 workers who have aged fish by inspecting the growth rings on 

 the scales or other hard parts, none has observed a specimen 

 which spanned the centuries. Direct observation by aquarium 

 curators throughout the world has led to the same conclusion 

 (S. Hinton, unpubHshed). Only 21 of 328 species reported 

 lived longer than 20 years. The oldest fish was a sturgeon 

 (Acipenser ruihenus) in the Royal Zoological Society Aquarium 

 in Amsterdam, Holland, which lived for 69 years and 8 months. 

 The cause of death was not reported for any species in the list. 



On the other hand, Orton's views have led to some hard 

 thinking. There have been several attempts to learn whether 

 or not fishes "over-reproduce" to the point where the effort 

 interferes with other life functions. As we shall see, some 

 studies affirm while others negate this point of view. 



Variability. There is a tremendous variation in fecundity, 

 not only in different species but within the same species from 

 place to place and among individuals of the same size. This 

 variation immeasurably complicates studies on the effect of 

 age on fecundity, and as a result the critical studies are of a 

 statistical nature. The following sources of variation should 

 be kept in mind while reviewing the evidence. 



1. Size variation. Fecundity increases as the length and 

 weight of the fish increases. 



2. Individual variation. Every fecundity study has 

 demonstrated a great individual variation in fecundity for 

 fish of the same length and of the same weight. 



3. Geographical variation. The fecundity of individuals of 

 comparable size varies considerably from one locality to 

 another. Maar's (1949) work on the char (Salmo alpinus) of the 

 Faxalven Water System, Sweden, has shown that the egg 



