494 
PACIFIC SCIENCE, Vol. XXI, October 1967 
Two other predators, wahoos and adult pilot- 
fish (with sharks), actively chased smaller 
fishes at the raft, but were not observed to 
catch any. 
Although zooplankton was not concentrated at 
the raft, a number of fishes that eat zooplankton 
gathered there. For example, stomachs of 10 
rough triggerfish caught at the raft contained 
many pteropods and stomatopods, and lesser 
numbers of crab megalops and zoea, amphi- 
pods, and copepods. Stomachs of 81 freckled 
driftfish contained small pelagic tunicates 
( Oikopleura sp.), copepods, fish eggs, chaeto- 
gnaths, and various coelenterates. These fish 
also bit at macroplankton such as ctenophores 
and tunicate colonies. Stomachs of 24 damselfish 
contained only Oikopleura sp. Stomachs of nine 
small pilotfish contained mostly copepods. All 
of these fishes, and also scrawled filefish and 
goatfish, frequently darted after and caught 
zooplankton around the raft. The wind slowly 
pushed the raft through the water at a speed 
faster than the swimming speed of the small 
zooplankters. Thus, there was no accumulation 
of zooplankton, but rather a continuous stream 
of macroplankton and microplankton slowly 
moving past the underwater windows. 
Finally, fishes at the raft did not feed on the 
small amounts of sessile or ambulating biota 
present. Only the rough triggerfish bit at the 
raft. Crab megalops occasionally settled on the 
underside of the raft or on the triggerfish, but 
those in the stomachs could have been taken 
as well from the plankton as from the raft. 
Perhaps a greater growth of biota on the raft 
would have altered the feeding behavior, es- 
pecially of the triggerfish, which has a dentition 
suited for grazing. Evans (1955) reported that 
triggerfishes (Balls tes sp., and Canthidermis 
sp.) cropped barnacles fringing the waterline 
of a drifting vessel in the Atlantic North Equa- 
torial Current. 
Removal of Ectoparasites 
At the beginning of this study we hypoth- 
esized that floating objects serve as cleaning 
stations where fishes may gather to have para- 
sites removed by other fish. Many fish observed 
at the raft carried ectoparasites, and several 
events suggested that these were eaten by other 
fish. Fish also chafed against the raft, another 
possible aspect of cleaning behavior. 
Small copepods were found on captured 
dolphins, freckled driftfish, and rough trigger- 
fish, and were seen on whitetip sharks and 
juvenile dolphins (Coryphaena sp.). Crab 
megalops and parasitic isopods were also seen 
on triggerfish. The megalops walked freely over 
the fish; the isopods were firmly attached. 
Biting behavior was common among rough 
triggerfish and was directed toward a trigger- 
fish that was headstanding (body oriented head 
down), apparently soliciting predation on para- 
sites. This behavior occurred only when more 
than one triggerfish was present; it was common 
3 to 12 m from the raft. The headstanding 
fish did not flee the biting fish and once even 
appeared to rotate its body, keeping the side 
with the parasitic isopod toward the biting fish. 
The biting was always directed at the headstand- 
ing fish even though several other fish were 
very close by. Although we did not witness 
directly the removal of a parasite, we saw one 
rough triggerfish bite at a parasitic isopod on 
the caudal peduncle of another, and soon after- 
ward the isopod was missing. Biting did not 
appear to represent aggressive behavior; intra- 
specific aggression among triggerfish frequently 
occurred immediately under the raft, but did 
not include headstanding. In aggression one 
triggerfish repeatedly chased others from under 
the raft. 
Once a rough triggerfish swam to a dolphin 
and apparently nipped at it. The dolphin, some 
distance from the raft, had begun leaning to 
one side. It had also stopped swimming and 
was almost motionless in the water. It leaned 
four times within 2 minutes, for periods of 
about 9 seconds. Similar leaning behavior by 
dolphins in the presence of rough triggerfish 
was seen on several other occasions, but did 
not elicit nipping by the latter. This behavior 
was not unlike that of inshore fishes soliciting 
parasite-cleaning labrids (Randall, 1958). Ba- 
listids are not among the reported inshore 
parasite-pickers, but their dentition should 
make them efficient in this role. 
A juvenile dolphin, Coryphaena sp., with a 
small reddish copepod attached near the fork 
of the caudal fin repeatedly positioned itself 
so that its caudal fin was close to the head of 
