206 Shelby D. Gerking 



the relative amounts of connective tissue. This would have to 

 be done in maturing ovaries where maximum egg diameters 

 could be measured at the same time. 



There seems to be no reason to continue studying fecundity 

 of egg-laying fishes with respect to age for gathering evidence 

 for or against the ageing process. Individual variation masks 

 any effect that age may have. Great variation plus the 

 difficulty in collecting a sufficiently large number of old 

 individuals makes it very improbable that this line of research 

 will ever become profitable. 



Summary 



Nutrition and reproduction of fishes are reviewed in relation 

 to age. A decline in the ability to utilize protein for growth 

 is exhibited as fish grow larger and older. This conclusion 

 is based on laboratory feeding experiments on the longear 

 sunfish (Lepomis megalotis), green sunfish {Lepomis cyanellus), 

 bluegill sunfish {Lepomis macrochirus), and red hind [Epine- 

 phalus guttatus). 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 reproductive capacity of live-bearing fishes of the family 

 Poeciliidae declines with age and there may be a period of 

 sterility before death. These results were obtained by field 

 observations and laboratory experiments on the fecundity of 

 the western mosquitofish, Gambusia affinis. Scattered ob- 

 servations among other species in the family agree with this 

 viewpoint. 



The effect of age on fecundity in egg-laying fishes is not 

 yet clear. The number of eggs in three-year sea-life sockeye 

 salmon (Oncorhynchus nerka) is significantly lower than in 

 two-year individuals. The same general phenomenon has been 

 said to be true of haddock {Melanogr animus aeglefinis), but 

 there is some doubt about this conclusion since statistical 



