460 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



The data given in table 2 are from several 

 sources. Undoubtedly exhaustive search of the 

 literature would reveal more data on the subject; 

 however, these suffice to give a general picture. 

 Because data on ova size are missing or very 

 scanty for several species we have included length 

 and weight of sac fry and free-swimming fry. 



Egg size, in general, is correlated with the 

 average size of the species. Thus Oncorhynchus 

 tshawytscha, the largest species, has the largest 

 This is, however, only a generalization. 



ova. 



It may be noted that the fry of the small pink 

 salmon, 0. gorbuscha, are larger than those of the 

 Atlantic salmon, Salmo salar. That is, the tend- 

 ency toward large eggs and fry appears to be a 

 characteristic of the genus Oncorhynchus. Be- 

 cause of the scarcity of data from actual measure- 

 ment of diameters of mature eggs, it is felt that 

 the scattered material brought together in table 

 2 cannot be wholly relied on to give a true picture 

 of egg size. However, corroborative evidence 

 can be obtained by an indirect method. 



In figure 6 (data from appendix table 4), the 

 average number of eggs is plotted against the 



2 3 4 5 6 



AVERAGE WEIGHT (KGJ 



Figure 6. — Relation, by species, of average egg number 

 to average weight. (Data from appendix table 4.) 



average weight of the females for each species. 

 (See also appendix tables 1, 2, and 3 for detailed 

 information on egg numbers, by species and 

 locality.) Obviously the data fall into two 

 general groups: fluvial anadromous Oncorhynchus, 

 which show a low number of eggs for their weight, 

 and lacustrine anadromous sockeye and members 

 of the other 3 genera, which show a large number 

 of eggs for their weight. That this difference in 

 egg number for comparable weights is not due to 

 a difference in the shape of the fish is indicated 

 by the very close correspondence between the 

 length-weight relation for all of the genera (fig. 7, 

 data from appendix table 5). 



3.0 



o 

 o 



1.4 1.6 1.8 



LOG OF FORK LENGTH (CM.) 



2.0 



Figure 7. — Relation, by species, of the logarithm of 

 mean weight to the logarithm of mean fork length. 

 (Data from appendix table 5.) 



It must therefore be concluded that the lower 

 egg number in the fluvial anadromous species of 

 Oncorhynchus can be due only to one of two 

 causes: either the eggs form a smaller percentage 

 of the total weight of the fish or the eggs are 

 considerably larger. Despite the paucity of 

 available information, the true cause of the 

 lower egg number in these species can be confi- 



