456 
Structural Changes Associated with 
Change of Colour Pattern 
These changes did not appear to be entirely 
due to sexual dimorphism and may have been 
influenced by developmental factors. The most 
striking changes are seen in the adult male, in 
which the profile of the head becomes increas- 
ingly obtuse. In many cases the convexity of 
the upper and lower profiles of the head is de- 
veloped to such a degree that the appearance 
of the head is completely altered. Such changes 
also occur, although to a lesser degree, in large 
females. In large males the upper limb of the 
preoperculum is more nearly vertical than that 
of the female, this probably being due to the 
increased obtuseness of the snout and the pro- 
portional changes associated with it. 
Disjunctive Distribution of the Sexes 
Adult males were usually obtained only from 
deeper water. The fact that shallow water col- 
lecting stations (especially over sandy bottoms 
in the vicinity of wharves and docks) revealed 
mainly females between 70 and 200 mm T.L. 
was thought at first to be due to a size selection 
factor imposed by the gear used. However, un- 
derwater observation confirmed the supposition 
that this habitat was populated mainly by in- 
dividuals not exceeding 200 mm T.L. and dis- 
playing an A colour pattern. A few individuals 
approximately 200 to 240 mm T.L. displaying 
a B pattern were seen, but these were rather 
exceptional. Collection from deeper water (in 
the order of six fathoms ) , away from the vicin- 
ity of wharves and shoreline rocks, revealed the 
presence of a much larger population of large 
fish, the majority of them being males. This 
situation obtained in most habitats sampled 
but was more pronounced in sheltered bays and 
harbours with a uniform sandy bottom. 
Hiatt and Strasburg (1957:133) record a 
rather similar situation in their work on Gom- 
phosus. The adult male or "tricolor” phase was 
observed mainly in the deeper parts of the 
range and was uncommon even there. This was 
confirmed by the author while making field 
observations at Heron Island on the Barrier 
PACIFIC SCIENCE, Vol. XIX, October 1965 
Reef. Such a distribution is even more pro- 
nounced in the case of Stethojulis strigiventer , 
which Randall (1955) has shown to be sex- 
ually dimorphic. The immature and adult fe- 
males bearing the "strigiventer” colour pattern 
were found to be common on the reef flat dur- 
ing both high and low water and, indeed, rep- 
resented one of the most abundant species noted 
there. The adult male or "renardi” phase ap- 
peared to be almost absent from the reef flat 
and, although observed in reef crest pools and 
on the outer slope, was nowhere abundant. 
SUMMARY 
( 1 ) The temperate labrid fish P. celidotus 
occurs in two distinct colour phases which, for 
the purposes of this study, have been designated 
Phase A and Phase B. 
(2) Specimens displaying a colour pattern 
transitional between A and B are observed. 
(3) Examination of the colour pattern, go- 
nads, and size range of a series of specimens 
indicates that the colour differences are due 
to sexual dimorphism. 
(4) The B colour phase is characteristic of 
sexually mature males larger than 160 mm T.L.; 
the A colour phase is characteristic of imma- 
ture and mature females smaller than approxi- 
mately 240 mm T.L. and some mature males 
smaller than 160 mm T.L. Females larger than 
240 mm T.L. may assume the B colour phase. 
(5) A notable feature is the lack of males 
below 104 mm T.L. It is postulated that the 
species is progynous and that all specimens be- 
low 100 mm T.L. are females. 
(6) The sexes have a disjunctive distribu- 
tion, adult males being usually confined to the 
deeper parts of the range, usually in excess of 
4-5 fathoms. 
REFERENCES 
Hiatt, R. W., and D. W. Strasburg. 1957. 
Sexual dimorphism in the labrid fish Genus 
Gomphosus. Pacific Sci. 11 ( 1 ): 133-134. 
Hutton, F. W. 1904. Index fauna Novae Zea- 
landiae. The fishes, pp. 40-55. Government 
Printer, Wellington. 
