The Biology of Senescence 



But in many unfished populations of other species there is a 

 steady increase in mortality with increasing age and size 

 (Ricker, 1948). 



A great deal of important information upon fish growth was 

 collected by Schmalhausen (1928) from the data of a number 

 of Russian workers (e.g. Tereschenko, 1917). In the sturgeon, 

 growth continues actively throughout at least 30 years of life, 

 with little decline in rate at sexual maturity (about 15 years). 

 In the bream, on the other hand, the growth constant shows 

 a more regular and progressive decline. These fish were found 

 to mature at about 3 years, and degenerative changes in the 



10 



0-5 



*1, 





oTTj « o 



& MLgj^ ' nu l u n *-* 



I I I I I I I I 1 I I I I I I I 1 I I I 1 I 1 I I 1 I I I I 



1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 



Age in Years 



Fig. 17 (a). — Growth-constant for growth in length of the sturgeon, 



Acipenser stellatus, at various ages. Broken line — females: single points — 



males: thick line, mean value for males; dashes, mean value for females. 



K x - 0-67, K 2 = 0-58 (from Schmalhausen, 1928). 



gonad were usually evident from the sixth year on — two definite 

 stadia could be observed in the growth curve, one following 

 puberty, and the other following this gonadal senescence, the 

 growth coefficient settling down to a steady value thereafter 

 without further decline up to 13 years of age (Fig. 17#, b, c). This 

 rather closely resembles the pattern reported in the goldfish. 



In Xiphophorus and Lebistes the male exhibits sharp specific 

 size, but the female may continue to grow measurably through- 

 out life, the pattern of growth differing little from that of the 

 plaice (Wellensieck, 1953). Yet in these forms previous experi- 

 ence suggests that there is no striking difference between the 

 survivals of the two sexes in captivity (Bellamy, 1934). In 

 Heterandria both sexes reach a virtual limiting size (Wellensieck, 



72 



