Bilateral Asymmetry in Paired Meristic Characters 
of Pacific Salmon 
B. J. Landrum 1 
ABSTRACT: The presence, extent, and direction of bilateral asymmetries of 
lateral line scales, gill rakers, branchiostegal rays, and pectoral fin rays of sockeye, 
chum, and pink salmon were examined. Some asymmetries were found in all char- 
acters in each species. Asymmetries, considering all species combined, occurred in 
approximately 72% of the lateral line scale comparisons, 59% of the gill raker com- 
parisons, 70% of the branchiostegal ray comparisons, and 26% of the pectoral fin 
ray comparisons. Bilateral variation in these characters was not conclusively related 
to sex of the specimens; however, some tendency toward greater asymmetry in 
branchiostegals of females was shown. Complete evaluation of this tendency will 
require further examination. 
Occurrences of asymmetries were evaluated in relation to the reliability of sub- 
stituting counts from the opposite side when the chosen side was lost or severely 
damaged. Substitution of lateral line scales of sockeye salmon appeared to be 
feasible, but in chum salmon the right side counts were significantly greater. 
(Scale counts from pink salmon were not available, because of the extreme dif- 
ficulty in obtaining reliable counts of the characteristically small scales.) Gill raker 
counts from sockeye salmon were found not to be interchangeable, as the right 
side counts significantly exceeded those of the left. In pink and chum salmon, 
bilateral variations in gill rakers appeared to be equal. Branchiostegal counts from 
the left sides of all species were significantly greater than those of the right. It was 
indicated that, for all species, pectoral fin ray counts from either side could be 
substituted reliably. 
Bilateral asymmetry in various body parts 
has been recognized in many animals that have 
a bilaterally symmetrical form of development. 
The extent and cause of many asymmetries have 
not been defined. Asymmetries of fish in the 
order Pleuronectiformes (flatfish) result in nor- 
mally dextral or sinistral individuals and have 
been attributed generally to the processes of 
natural selection and adaptions of the organism 
to life on the ocean bottom. Hubbs and Hubbs 
(1944:303), emphasizing the morphology of 
flatfish, have pointed out that some asymmetries 
appear in many body parts of all fishes, both 
externally and internally. In studies on meristic 
and other characters of four species of chars, 
Vladykov (1954:910) has noted somewhat 
1 Biological Laboratory, Bureau of Commercial 
Fisheries, 2725 Montlake Boulevard East, Seattle, 
Washington. Manuscript received November 17, 
1964. 
higher gill raker counts on the right sides. In 
Pacific salmon bilateral asymmetry of branchi- 
ostegals, in which the left side overlaps the right 
anteriorly and contains more rays, has been de- 
scribed by Jordan and Evermann (1896:479). 
As a consequence of these known asymme- 
tries in fish, morphological characters from both 
sides of all species, ideally, should be examined 
for taxonomic and racial studies, or examination 
should be limited to one chosen side. If the lat- 
ter alternative has been adopted, problems arise 
if the chosen side is mutilated or otherwise un- 
obtainable. In racial studies on Pacific salmon 
(Fukuhara et al., 1962), data on various meristic 
characters were arbitrarily collected from the 
left side of all specimens. The racial study in- 
volved multivariate analysis of data from sev- 
eral meristic characters; therefore occasional 
failures to obtain information from any one lost 
or damaged character prevented the specimen’s 
193 
