GROWTH AND MATURITY OF SALMON IN THE OCEAN 
29 
RELATIVE MATURITY OF CHINOOK SALMON TAKEN IN THE OCEAN 
It has been shown above that the determination of the degree of maturity is 
accomphshed primarily by comparing the distribution of the egg sizes of a group 
of fish with the simihir distribution of fish known to be mature. It has been pointed 
out that the size of the eggs changes during the season; that there are difi'erences 
in the size of eggs of fish of different ages, due to the difl^erence in the size of the fish; 
and also there are racial difi^erences in the size of the eggs. It is obvious that these 
factors will make it impossible to draw a sharp line of distinction, which will hold 
good throughout the season, between the size of the eggs of mature and immature 
fish, and that the determination of the relative maturity of the fish taken in the 
ocean must depend upon a comparison of the distribution of egg sizes in the various 
age groups with the distribution of egg sizes of unquestionably matxu-e fish taken 
in the river at about the same time of the year. This has been done in the deter- 
mination of relative maturity given below. 
FISH IN THEIR SIXTH YEAR, OCEAN NUCLEI 
Only two females of this age group were taken in the collection studied. One 
was taken on July 28, 1919, and the other September 18 or 19, 1919. Both were 
undoubtedly mature. The logarithm of the diameter of the eggs (log D) was 0.69 
in the first specimen and 0.77 in the second. No fish of this age group appear in 
the collections taken inside the river near these dates, but four specimens are found 
in a collection made June 24 and 25, 1919, and three in one made July 3. The 
average log D in these collections was, respectively, 0.55 and 0.657. The maximum 
age attained by the chinooks of the Columbia River is 6 years, and comparatively 
few fish of this age are foxmd. It is, therefore, quite to be expected that any fish 
of this age group which might be taken in the ocean would be maturing. 
FISH IN THEIR FIFTH YEAR, OCEAN NUCLEI 
As has just been indicated, very few fish with oceeai nuclei older than 5 years 
are found in the Colxunbia River run. It was, therefore, to be expected that nearly, 
if not quite all, of the fish of this age gi'oup which are taken outside would be matm- 
ing, and such was found to be the case. No inunature fish of this age group were 
found. Figure 4 shows the average log D for the collections of fish taken outside 
and also for those taken inside throughout the season. The figure shows clearly 
that there are only negligible differences in the sizes of the eggs of the fish taken in 
the two localities. 
FISH IN THEIR FOURTH YEAR, OCEAN NUCLEI 
The determination of the relative maturity of the fish of this age group has 
proved more difficult and the results are less satisfactory than with any other cate- 
gory. The number of fish belonging to this age group, which were taken in the 
ocean and which were with certainty immature, is small. Thexe must, however, 
be a considerable proportion of the 4-year fish with ocean nuclei that do not mature 
during their fourth year, since there is a rather high percentage of fish in their 
3210°— 25t 2 
