NOTES 
Sexual Dimorphism in the Labrid Fish Genus Gomphosus 1 
During an examination of the viscera of 
Marshallese fishes the writers’ attention was 
drawn to the fact that all of our specimens of 
Gomphosus varius in which the sex could be de- 
termined were females, and that all specimens 
of G. tricolor were males. Suspecting the possibil- 
ity of sexual dimorphism, we collected addi- 
tional material, so that this study of Gomphosus 
ultimately included 56 specimens from Eniwe- 
tok, 4 from Bikini, 3 from Arno (all atolls in the 
Marshall Islands), and 15 from Oahu and Kauai 
in the Hawaiian Islands. Seven Marshallese and 
3 Hawaiian specimens were tricolor , according to 
various descriptions; 14 Marshallese specimens 
were the distinctively marked juveniles of varius\ 
and the remaining 54 were typical varius. Eight 
of the 10 tricolor proved to be males, one was 
decomposed internally, and another was too 
immature to be sexed. Sex could not be deter- 
mined for any of the 14 juvenile varius , but 39 
of the larger specimens were females in various 
stages of maturity while 15 were immature and 
could not be sexed. 
The major taxonomic difference between tri- 
color and varius is color and color pattern. In 
life tricolor is a rich blue-green with a vertical 
yellow-green bar across the trunk near the 
pectoral insertion. Its head and caudal fin tend 
to be rather more bluish than the rest of the 
body, and in large specimens the caudal fin is 
somewhat lunate. G. varius is somberly colored 
in comparison, being plain black posteriorly and 
creamy white to light brown anteriorly, each 
antero-dorsal scale having a dark spot at its 
base. The breast and cheeks are white or cream, 
the snout tip is reddish, and a narrow black 
stripe runs the length of the head at the level 
of the pupil. Small juveniles of varius are bright 
yellow-green dorsally, plain white laterally and 
ventrally, and have a pair of lengthwise black 
1 This paper is Contribution No. 86, Hawaii Marine 
Laboratory, in cooperation with the Department of 
Zoology and Entomology, University of Hawaii. The 
senior author was a member of the staff of Duke Uni- 
versity at the time the work was done. Manuscript 
received August 7, 1956. 
stripes from the snout tip to the caudal base. 
They also differ from larger specimens in that 
they either lack or are just developing the 
elongate snout characteristic of the genus. Jor- 
dan and Evermann (1905. U. S. Fish Comm ., Bui. 
23: pi. 36) present a color plate of tricolor and in 
the same work {op. cit., p. 289, fig. 125) a black 
and white drawing of varius. 
In size, our tricolor range from 104 to 166 mm. 
in standard length, whereas typical varius range 
from 38 to 134 mm. From about 30 to 40 mm. 
the varius and juvenile color patterns intergrade, 
our largest true juvenile measuring 36 mm. and 
the smallest 23 mm. Similarly, but on the other 
end of the scale, our smaller tricolor show un- 
mistakable vestiges of a varius color pattern, the 
persistent elements being the basal dark spots 
on the anterior trunk scales. These spots are 
more obvious in preserved material than in fresh 
specimens but some indication of their presence 
occurs on all tricolor examined. The largest tri- 
color have slightly lunate caudal fins, a condition 
often appearing with age or sex in fishes, and 
here it is apparently restricted to the male. 
Meristic data are the same for the two forms, 
based on 10 tricolor and 19 varius. Dorsal rays 
are VIII, 13; anal rays III, 11 (the first spine 
is imbedded) although one tricolor had only 10 
anal rays; pectoral rays are 16, including the 
short bony splint at the top of the fin, with an 
occasional specimen having 15 or 17 rays; and 
lateral line scales are 27. The gill arches are 
C-shaped and not readily divisible into upper 
and lower limbs. Gill rakers totalled 24 for the 
first arch in the two varius and two tricolor 
examined for this feature. 
The above facts point to the hypothesis that 
in the Hawaiian and Marshall Islands, at least, 
the species of Gomphosus hitherto regarded as 
tricolor and varius are in reality the two sexes of 
the same species. Apparently tricolor represents 
mature and nearly mature males while varius 
includes all females and probably also young 
males (even though no recognizable males were 
found with typical varius coloration). Mature 
males are somewhat larger than the largest fe- 
133 
