Bilateral Asymmetry in Salmon — Landrum 199 
TABLE 2 (continued) 
Combined chum 
samples 
male 
female 
total 
166 
186 
352 
53.0 
55.9 
54.5 
42.0 
48.1 
45.3 
-.138 
-.038 
-.085 
> 5 
>50 
> 5 
Petersburg 
pink 
male 
37 
54.0 
60.0 
.027 
>50 
(1959) 
female 
18 
72.2 
61.5 
.111 
>50 
total 
55 
60.0 
66.6 
.054 
>50 
Fraser River 
pink 
male 
31 
64.5 
60.0 
.064 
>50 
(1959) 
female 
18 
50.0 
55.6 
.056 
>50 
total 
~ 49 
59.2 
58.6 
.061 
>50 
Combined pink 
male 
68 
58.8 
60.0 
.044 
>50 
samples 
female 
36 
61.1 
59.1 
.083 
>50 
total 
104 
59.6 
59.7 
.058 
>50 
eye salmon examined. Of specimens exhibiting 
asymmetry, 58% had larger left side counts. In 
the combined data for the species, left side 
counts exceed the right by 0.15 rakers, which 
was significant at the 0.01 level. 
In chum salmon (Table 2), the mean differ- 
ences between left and right side gill raker 
counts were significant for only one sample col- 
lected on the high seas in 1956. Mean differ- 
ences and probability levels varied among the 
samples of both males and females, with no ap- 
parent evidence of sexual dimorphism. The 
probability level for the mean differences calcu- 
lated for all males combined was greater than 
5%, and for all females was greater than 50%. 
Of the total of 352 pairs of chum salmon gill 
raker counts, 54% showed asymmetrical de- 
velopment of the structures. Asymmetry was 
toward the right side, which averaged 0.085 
more rakers in these specimens; however, this 
difference was not significant. 
In pink salmon (Table 2), differences be- 
tween left and right side gill raker counts varied 
little among the categories of sample location 
or sex. In this species, 59% of the males and 
61% of the females examined showed some 
asymmetry in gill raker counts from opposite 
sides of the fish, with a slight but consistent 
tendency for the left side to exceed the right. 
The probability levels for the samples and for 
all specimens combined, however, indicated that 
the observed mean differences were not statis- 
tically significant. 
Bilateral Variations in Branchiostegal Rays 
Pairs of branchiostegal ray counts were col- 
lected from 407 sockeye, 350 chum, and 59 pink 
salmon (Table 3). Although very few speci- 
mens of pink salmon were examined, in this 
species, as well as in the other two, the females 
exhibited a greater percentage of asymmetrical 
development, with larger mean differences than 
the males. Only in sockeye samples from the 
Karluk and Egegik rivers, and in one chum 
salmon sample taken by the MV "Celtic,” was 
the trend reversed. The mean differences ob- 
served were significant for all individual sam- 
ples and also for each sample of male or female 
fish. In the combined data for each of the three 
species, asymmetrical development occurred in 
62%, 77%, and 71% of the sockeye, chum, and 
pink salmon, respectively. Left side counts ex- 
ceeded right side counts in 93% of the asym- 
metrical pairs of sockeye salmon branchioste- 
gals, in 96% of the chums, and in 98% of the 
pink salmon. In sockeye salmon, the number of 
branchiostegal rays in the left side structures 
exceeded the right by approximately 0.6 rays; 
in chum and pink salmon the mean differences 
averaged 0.8 rays. The mean differences in all 
three species were statistically significant. 
Bilateral Variation in Pectoral Fin Rays 
Comparisons were made of fin ray counts 
from left and right pectoral fins of 407 sockeye, 
357 chum, and 97 pink salmon (Table 4). No 
consistent trends were observed toward sexual 
dimorphism or effect of sampling location in 
respect to asymmetry of this character. For the 
combined data for each species, asymmetry oc- 
curred in only 14-24% of the specimens — 
much less frequently than for the other three 
characters examined. Variations in the number 
of rays from opposite sides resulted in very 
