114 FRESHWATER ANIMALS 



systematics of this large number of very similar species has been 

 confused! 



Svardson (1952) was able to demonstrate the environmentally 

 determined plasticity of all these phenotypic characteristics by 

 transplanting stocks with well-known characteristics to lakes that 

 lacked Coregonus populations. Different and unrelated aspects of 

 the environment may affect the phenotypic expression of certain 

 of the above-noted plastic features. For example, the number of 

 scales along the body, a feature that has frequently been used 

 to distinguish subspecies and even species, was shown by Svard- 

 son to be affected both by temperature during development and 

 by the state of nutrition of the female parent. The eggs produced 

 by well-fed populations are larger than those of poorly fed ones, 

 and more scales are initially laid down in the larger fry that 

 develop from the larger eggs. 



The extraordinary plasticity of these fish can be seen in com- 

 parisons of specimens from such transplanted stocks with cor- 

 responding ones from the original populations. In Fig. 11B the 

 lower specimen is the normal size of a spawning whitefish from 

 Lake Lomsjon. When this stock was transplanted to Lake Oxvatt- 

 net, the normal size at spawning was that of the upper specimen. 

 Some stocks retain this plasticity into maturity, as is demon- 

 strated in Figure 11C. Spawning whitefish of Lake Naekten attain 

 the size indicated in the upper specimen. When adult fish from 

 this stock were transplanted to Lake Algsjo, they had, in two 

 summers, achieved the size of the lower specimen. Further dif- 

 ferences in growth, size, and length of life between populations 

 of the same species in different lakes can be seen by comparing 

 the graphs of Fig. 12. 



The studies on the environmental plasticity of these fish are 

 summarized by Svardson (1953, p. 165) with these words: 



. . . species of whitefish, which as far as can be judged must be the 

 same form from lake to lake, can have different forms in one lake or 

 another. The same species can have a long life or die young, grov 

 rapidly or have extremely poor growth, live in large or small popula- 

 tions, spawn in running or still water at different depths and at ex- 

 tremely varying times. Some variation is already found in the habits ol 



