NORTH AMERICAN SALMONIDAE 



261 



""■'o I 2 3 16 6 7 8 



AVERAGE FISH WEIGHT IN KILOS 



Figure 14. — Fecundity isopleths based on number of eggs 

 per kilo of total weight versus the average weight of 

 the adult tish. 



The genus Salmo presents a very different 

 picture. Of the three species, salar, trwtta^ and 

 gairdneri, S. tnitta shows connections with Salve- 

 Unus marstoni, only a remote affinity witli Sahno 

 solar, and none witli Salmo gairdvsri. Salmo 

 solar shows equally remote associations with Salm^ 

 trutta, Salvelinus aureolus, and Salmo gairdneri. 

 Salmo gairdneri is closely linked with Oncor- 

 hynchv^ {kisutch) on one hand and with Salve- 

 liniis {marstoni) on the other, and shows only a 

 remote affinity with Salmo salar and none with 

 Salmx) tnitta. 



FECUNDITY 



Although the term "fecundity" is normally used 

 to denote the numbers of ova produced, we must 

 also deal with the size of the ova. For each 

 species of Salmonidae there is a normal range for 

 both number and size of egg. For Oncorhynclvus. 

 which mature and spawn only once, this range is 

 not too difficult to define. For species that live to 

 spawn two or more times, the number of eggs 

 varies widely, since the number is correlated with 

 the weight of the fish (Rounsefell, 1957) . Size of 

 the egg is more constant for each species than the 

 number, but tends to be larger in larger 

 individuals. 



Most of the available data on fecundity in the 

 Salmonidae are given in some detail by IJounsefell 

 (1957). From these data the average fecundity 

 of the species for which data are available was 



plotted in figure 14. It will be noted at once that 

 the lowest number of eggs per kilo of fish weight 

 occurs in the fluvial anadromous Oncorhynchus. 

 That this lower number of eggs per kilo of fish 

 weight is not caused by a lower total weight of 

 ova but rather to larger individual eggs is shown 

 by figures 15 and 16, which show for available 

 data the number of eggs per kilo of fish weight 

 plotted against egg diameter and weight of fry, 

 respectively. 



Figures 15 and 16 show that the fluvial anadro- 

 mous Oncorhynchus differ markedly in egg size 

 from the other Salmonidae. The lacustrine ana- 

 dromous 0. nerka appears to be only slightly 

 ahead of i^. salar in egg size. 



f3 1000 



ALPIHUS O 



O • NAMAYCUSH 



O-MEiSUREO DIAMETER 

 • -CALCULATED DIAMETER 



500L 



4.0 



rSHAWYTSCHA • 

 J 1 I 



5 6.0 7 



EGG DIAMETER (MM.l 



FiQUKE 15.— Number of eggs per kilo of total weight 

 versus the egg diameter. 



% SALAR 



• eORBUSCHA 

 # KISUTCH 



KETA • 



J_ 



TSHAW1TSCHA 

 J 1 l_ 



20 30 40 .50 



WEIGHT OF FRY WITH YOLK ABSORBED (G) 



Figure 16.— Number of ei;gs per kilo of total weight 

 versus the average weight of fry after absorption of 

 the yolk. 



