FECUNDITY OF NORTH AMERICAN SALMONIDAE 



457 



These backward extensions of the ovaries are formed 

 by the maturing and enlarging ova filling the previously 

 crowded interlamina spaces at the posterior end of the 

 ovary, thus stretching it longitudinally. 



This increasing disproportion between the left 

 and right ovaries in fish with larger numbers of 

 eggs is logical since in a fish with few eggs the 

 posterior portion of the body cavity would be 

 relatively empty. Fish of the same size with 

 more eggs would have to utilize this space and the 

 left ovary, which is usually longer than the right, 

 would thus be proportionately larger. However, 

 for the chum salmon in Japanese waters, the data 

 of Eguchi et al. (1954) show no significant differ- 

 ences in egg number between the two ovaries. 

 For 243 chum salmon the averages are 1,134 in 

 the left ovary and 1 ,146 in the right ovary. Sock- 

 eye salmon from little Bare Lake in the Red River 

 system of Kodiak Island contain more eggs in the 

 right than in the left ovaries (personal commu- 

 nication from Philip R. Nelson). It is interesting 

 to speculate whether this is a genetic difference or 

 induced by the great environmental difference 

 between Bare and Karluk Lakes. 



Probably the best explanation of this dispro- 

 portion in the size of the two ovaries is given by 

 Brown and Kamp (1942, p. 196). In discussing 

 the brown trout, Salmo trutta, they say — 



In the brown trout, the posterior portion of the intestine 

 usually bends strongly to the right, thus crowding the right 

 ovary at its caudal end. The length of the ovary is in- 

 versely proportional to the degree of crow'ding. However, 

 the left ovary is not always the longer. One fish was 

 observed to have a longer right ovary and it was Interest- 

 ing to note that this specimen had an intestine which 

 bent to the left instead )f the right. In one or two fish 

 the ovaries were of approximately equal length, with the 

 jntestine bending neither to the right nor the left. 



They found in 8 brown trout averaging 36 cm. in 

 standard length that the right ovary was 133 mm. 

 long and weighed 32.4 grams, while the left ovary 

 averaged 169.5 mm. and weighed 42.6 grams. 



In discussing the effect of age at maturity on 

 number of eggs in Oncorhynchus there are two 

 questions: (1) Is the number of eggs determined 

 by length of residence in fresh water or length of 

 residence in the sea? (2) Does the number of 

 eggs for any given length of fish increase or de- 

 crease with age? These questions cannot be 

 answered by the pink salmon data because they 

 leave fresh water immediately after emerging 

 from the gravel, and because they invariably 

 mature in their second year. 



The following tabulation has been made for 

 the Karluk River sockeye salmon, showing the 

 average number of eggs in relation to the period 

 of residence of the salmon in fresh water and in 

 the ocean. 



' Since smolts enter the sea from early to late spring and reenter the rivers as adults from spring to early fall the ocean age gives number of ocean summers, 

 but 2 years at sea may vary from about 23 to 27 months. The growing seasons are of paramount importance to this discussion. 



* Fresh-water age' is from the lime the eggs are deposited (from late June to November) until smolts enter the sea (from May to July), so that a fresh-water 

 age of 3 can vary from about 29 to 3ii months in fresh water, but the sununers spent in the lake after hatching are the periods important to this discussion. 



3 Not corrected for length of fish. 



The data for 1940 and 1941 are for 60-cm. fish, 

 so to make the data for 1938 and 1939 comparable 

 to data for the other years it was necessary to 

 obtain the number of eggs for 60-cin. fish from 

 the regressions of eggs on length of fish. These 



regressions were computed separately for the 

 left and the right ovaries and the counts for each, 

 calculated from these regressions, were then 

 combined. 



In order to discount environmental effects the 



4273!>:5 O — 57- 



