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PACIFIC SCIENCE, VoL XII, October, 1938 
it passes posteriorly until it ends at rear of 
dorsal fin; head and thorax below level of 
lower edge of eye are pale; caudal fin black 
with narrow pale-violet edges ; dorsal and anal 
fins dusky basally and hyaline distally, the 
dorsal blackish anteriorly, the anal darker 
posteriorly; paired fins pale. 
Labroides caemleo-lineatus Fowler (1945: 65, 
fig. 7) (1946: 159) is a young L. dimidiatus. 
The description was based on a 28 mm. speci- 
men, and the figure clearly shows the typical 
juvenile color pattern as described above. 
L. dimidiatus occurs most commonly in 
coral or coral-sand areas which are protected 
from wave action. Around atolls individuals 
are most often seen in lagoons rather than 
outside the peripheral reefs. I have observed 
them in water as shallow as 2 feet and as deep 
as 120 feet, but they appear to be more 
abundant in shallow water. Regan (1908: 230) 
has recorded the species from 34 fathoms in 
the Maldives. 
Of this species de Beaufort (1940: 148) 
wrote, "In the aquarium of Amsterdam I ob- 
served that Labroides dimidiatus cleans the sur- 
rounding of the mouth and the gill openings 
of large fishes (Het Aquarium IV, 1936: 153) 
in the same way as has been observed by 
Beebe for the Atlantic species Iridio bivittatus. 
Smith (1949: 291) stated that L. dimidiatus 
"Feeds on minute organisms on rocks and 
has been observed to nibble over the mouth 
parts and gill covers of large Rock-cods." 
Doty and Morrison (1954: 24) observed what 
they termed an interesting association be- 
tween a parrot fish and a fish which is un- 
doubtedly L. dimidiatus } The latter "cleans 
2 These authors erroneously refer to this species as a 
blenny — probably because of the confusion that results 
from the similarity in color pattern of L. dimidiatus to 
the blenny Aspidontus taeniatus Quoy and Gaimard, a 
similarity so striking that Barnard (1927: 749) sug- 
gested that mimicry might be involved, with perhaps 
one or the other species being poisonous. R. W. Hiatt 
and D. W. Strasburg observed the resemblance at Arno 
Atoll in the Marshall Islands and suspected mimicry. 
Randall (1955 b: 144), noting it in the Gilbert Islands, 
proposed that the blenny might be mimicking the 
labrid, since the latter might gain protection from 
predaceous fishes by virtue of its food habits. 
off its larger companion’s beaklike jaws, teeth 
and head area.” They implied that this un- 
usual association is limited to just these two 
species; however, I have observed (Figs. 2, 3, 
5) L. dimidiatus picking at the heads, bodies, 
and fins of numerous species of reef fishes 
representing many different families, includ- 
ing the carangids and serranids, members of 
which habitually prey upon small reef fishes. 
None of the above authors mentioned the 
removal of ectoparasites; the use of the term 
cleansing gives the connotation of removal 
of debris or particles of food. 
The stomach contents of two specimens 
from the Gilbert Islands and three from the 
Marshall Islands consisted of calagoid cope- 
pods which are ectoparasitic on fishes; two 
more specimens from the Gilberts had eaten 
small isopods (also fish parasites) along with 
a few fish scales (Randall, 1955 b: 144). Sub- 
sequently, a specimen, 72 mm. in standard 
length, from Hull Atoll, Phoenix Islands, 
was found to contain three caligid copepods 
Fig. 2. A parrot fish, Scams sp. (upper fish), and a 
surgeon fish, Zebrasoma scopas (lower fish), each being 
examined for ectoparasites by Labroides dimidiatus. 
Reproduced from 16 mm. movie film taken in the 
lagoon of Takaroa, Tuamotus. 
