Sexual Dimorphism in the Labrid Fish Pseudolabrus celidotus 
(Bloch and Schneider) 1801 
J. H. Choat 1 
During a systematic study of New Zealand 
fishes belonging to the genus Pseudolabrus 
Bleeker 1861, it was observed that one of 
the commonest species, P. celidotus, occurred 
in two distinct colour phases. This was first 
noted by Richardson (1848) who described 
the two colour variants as separate species. The 
subsequent literature did not recognise these as 
species, but merely as varieties, although the 
true relationship was not clarified. A study of 
populations of this species, both in the field 
and in the laboratory, revealed that the colour 
differences were due to sexual rather than en- 
vironmental or geographic factors, and repre- 
sented a moderately developed degree of sexual 
dimorphism. An attempt has been made here 
to examine the relative proportions of each 
colour phase in selected populations, the se- 
quence of transition from one colour phase to 
the other, and the sizes at which transition 
occurs. 
The specimens required for the study were 
obtained by a variety of quite orthodox meth- 
ods, lining, spearing, trapping, and various net- 
ting techniques all being employed. Rotenone 
was successful in obtaining small specimens 
from enclosed rock pools but was less effective 
in open water. 
The genus Pseudolabrus comprises a number 
of predominantly temperate water labrids, the 
majority of which occur in the coastal waters 
of New Zealand, Tasmania, and Southern Aus- 
tralia. They are almost completely absent from 
waters supporting coral reef formations al- 
though they have obvious affinities with the 
tropical Indo-Pacific labrids. P. celidotus shares 
the following characters with the majority of 
1 Department of Zoology, University of Queens- 
land, Brisbane. This study was carried out at Victoria 
University, Wellington, New Zealand, and constitutes 
a portion of a thesis towards the degree of M.Sc. Man- 
uscript received October 18, 1963. 
other members of the genus: D. IX/11; A. 
Ill/ 10; operculum fully scaled; a series of small 
imbricate scales on the cheek; two pairs of 
anterior canines in each jaw; a posterior canine 
in each angle of the jaw; an inferior pharyn- 
geal bone bearing a strongly developed ante- 
rior shaft; a continuous lateral line. 
For the purposes of this study the colour 
phases were designated simply Phase A and 
Phase B. The characteristics of each follow. (In 
each case the descriptions have been furnished 
from fresh material.) 
Phase A ( Fig. 1 ) 
General body colouration ranging from pale 
whitish grey to yellowish green, usually with a 
black centre in each scale, these becoming more 
pronounced dorsally. Dorsum varies from dusky 
grey to black with the interorbital and occipital 
regions darker than the rest. Throat, isthmus, 
thoracic, and abdominal regions range from 
almost white to pale yellow, the sides of the 
abdomen often shaded by a reddish tint. A 
single prominent black blotch below the sev- 
enth to ninth dorsal spines, extending one scale 
row above and two scale rows below the lateral 
line, and covering the ninth to twelfth lateral 
line scales. Four dark transverse bars on the 
posterior portion of the body, often becoming 
indistinct in specimens exceeding 150 mm T.L. 
The first bar extends from just below the lat- 
eral blotch to a point level with the peduncle 
of the pectoral fin. The second extends from 
below the sixth to seventh dorsal rays to three 
or four scale rows below the midline of the 
body. The third extends from just below the 
termination of the dorsal fin to the region of 
the termination of the anal fin. The fourth bar 
is often diffuse and indistinct, and usually cov- 
ers the last two or three transverse rows of 
scales on the caudal peduncle. Two prominent 
black postorbital bars, the first extending from 
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