Review of Labroides — RANDALL 341 
TABLE 1 
Gut Contents of Specimens of Labroides phthirophagus 
DATE 
COLLECTED 
STANDARD 
LENGTH 
(mm.) 
SEX 
GUT CONTENTS 
Apr. 10/50 
58 
F(ripe) 
2 calagoid copepods, 4 larval gnathiid isopods, fish scales 
Sept. 21, ’51 
53 
F 
4 calagoid copepods, 25 harpacticoid copepods* 
May 11/52 
60 
F 
3 calagoid copepods, 1 lernaeid copepodf, 88 lichomolgid 
copepodsf 
Dec. 31/52 
42 
M 
2 calagoid copepods, 1 lernaeid copepodf 
49 
F 
14 calagoid copepods, 1 lernaeid copepodf, 4 larval gnathiid 
isopods 
55 
F 
10 calagoid copepods, 1 lernaeid copepodf, 6 larval gnathiid 
isopods, fragment of fin membrane 
76 
M 
2 calagoid copepods, 14 digenetic trematodes§ 
Jan. 21, ’53 
39 
F? 
1 calagoid copepod, 8 larval gnathiid isopods 
June 19/53 
60 
F 
1 calagoid copepod, 19 harpacticoid copepods* 
July 25/55 
58 
F 
6 calagoid copepods, fish scales 
Aug. 7/55 
63 
F 
14 calagoid copepods 
* Tisbe sp.; most species are free-living but at least one is commensal (in a pelecypod) . 
f Peniculus sp., generally attached to fins. 
f Many members of this family of cyclopoid copepods live commensally with tunicates, pelecypods, flatworms, etc.; how- 
ever, according to Dr. Paul L. Illg, this species of copepod does not fit well into any genus so far proposed. Although no 
lichomolgid has turned up as parasitic on a vertebrate, this one is sufficiently distinctive anatomically ( the arrangement of 
the maxillary suggests its use as a substitute masticatory appendage) that it might have developed a divergent feeding 
mechanism. 
§ Undigested, probably a gut parasite of the Labroides. 
moorish idols and the trigger fish were im- 
mediately aware of the new arrival, for they 
reacted as in the normal environment. As the 
Labroides swam past individual fish, many 
were observed to cease swimming, and oc- 
casional moorish idols stopped their respira- 
tory movements and raised their gill covers. 
The following morning the Labroides could 
not be found in the aquarium. 
The second Labroides was added to a tank 
containing two parrot fishes ( Scarus sp.) about 
250 mm. in length and seven surgeon fishes 
(. Acanthurus spp.). Again the Labroides paid 
little heed to the other fishes, but they reacted 
characteristically. The surgeon fishes swam 
about nervously in a restricted area of the 
tank. The behavior of the parrot fish was al- 
most ludicrous. They followed the Labroides 
around the aquarium, stopping occasionally 
to literally stand on their tails, waggle their 
pectoral fins, and seemingly to ogle the 
labrid, as if to entreat it to perform the ex- 
pected services. The parrot fishes and surgeon 
fishes were recognized as ones which had 
been in the aquarium at least several months. 
This poses a question which is as yet un- 
answered. Do these fishes learn the role of 
Labroides through experience or is their be- 
havior innate? The answer could be provided 
through observation of Labroides phthiropha- 
gus with aquarium-reared fishes or with fishes 
taken from an area where species of Labroides 
are known not to occur. If learned through 
experience, how long is the capacity for 
symbiotic association retained? 
The second Labroides was left overnight in 
the aquarium, and it also was gone the next 
day. It is not known whether this and the first 
Labroides which disappeared were eaten by 
fish or whether they escaped down the drains 
(which, it was later noted, were not screened). 
The third Labroides was placed in an aquar- 
ium containing only adult wrasses of many 
species. It was immediately chased about the 
tank by several individuals of different spe- 
cies and ultimately eaten by one of them. 
This was totally unexpected, for various 
wrasses were among the fishes which were ob- 
served being serviced by Labroides phthiropha- 
gus in the reef environment. The immediate 
