The Biology of Senescence 



record of longevity appears to be between 30 and 40 years. 

 Rate of growth is extremely variable. One specimen, kept in 

 a six-gallon tank, reached a length of only 4 inches in 25 years 

 (Hervey and Hems, 1948). 



In none of these cases is it clear how large a part of the 

 potential life-cycle is actually covered by the observed growth 

 curve. In most fish the rate of growth does in fact decline with 

 age, though in many the effective reproductive life appears to 



300 



2-00 - 



POO 



7 2 3V 

 Age in YeGrs 



10 11 12 13 



Fig. 17 (c). — Growth in weight of the Bream (Abramis brama) — annual 



increments. The mean growth-coefficients at various stadia (youth, 



maturity, postreproductive life) are indicated by transverse lines K lf 2j 3 



(from Schmalhausen, 1928). 



have ceased long before this decline has produced an almost 

 stationary body-size. The reproductive decline, moreover, 

 does not appear to involve any decrease in vigour, and may 

 actually imply the reverse, in view of the hazards which repro- 

 duction involves for many fish. 



In the small teleosts, it ought to be possible to answer most 

 of these questions by direct experiment. For this purpose the 

 guppy (Lebistes) is proving a particularly suitable experimental 

 animal, both because of the ease with which it can be reared 

 and handled for purposes of measurement, and because of the 



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