192 Shelby D. Gerking 



number per female may vary as much as fivefold in different 

 lakes of the same watershed. In fact, geographical variation 

 has been so prominent that "races" of some species have been 

 delineated partly on the basis of fecundity. Davis (1957) has 

 shown that the ova production of the American shad {Alosa 

 sapidissima) varies considerably from one river system of 

 the Atlantic Coast drainage to another, and McGregor (1923) 

 could distinguish certain river races of the king salmon 

 (Oncorhynchus tshawytscha) on the Pacific Coast on the basis 

 of egg counts. 



4. Year-to-year variations in the same locality. Individuals 

 of the same size may bear significantly different numbers of 

 eggs from one year to the next. This is true for the long 

 rough dab {Hippoglossoides platessoides) off the coast of 

 Scotland (Bagenal, 19576) and for the lake trout {Salvelinus 

 namayciish) of Lake Opeongo, Ontario, Canada (Fry, 1949). 



These wide variations in fecundity are usually explained on 

 the basis of genetic and dietary differences. The racial 

 studies imply that heredity is very important in determining 

 fecundity. Year-to-year variation has been attributed to dif- 

 ferences in the availability of food. Both sources undoubtedly 

 account for the fluctuations in the egg number of individuals 

 of the same size. 



Because of the complex nature of the information on 

 fecundity, evidence of the ageing process from a few species 

 in which fecundity has received considerable study will be 

 reviewed here. 



Methods of counting eggs. The usual methods of deter- 

 mining fecundity vary from counting the entire number of 

 eggs from both ovaries to counting samples from various 

 sections of one or both ovaries and computing the total 

 number of eggs on the basis of the sample. Three sampling 

 methods have been used: volumetric, dry weight, and wet 

 weight. In the first method the total volume of eggs is 

 determined in a graduated cylinder and the number in a 



