x, 59 leaves, bound : ill., maps ; 29 cm.Juvenile reef fishes often have a color pattern different from that of adults. It
has been theorized that this reduces the aggression received by juveniles from adult
conspecifics. This was tested using two species of Labroides cleaning wrasses in which
certain-sized individuals can quickly shift back and forth between the adult and juvenile
color patterns. Adult Labroides phthirophagus has the same single-male grouping
social structure as previously described for L. dimidiatus. Small L. phthirophagus and
L. dimidiatus in juvenile coloration shifted to adult coloration when isolated and then
quickly shifted back to juvenile coloration when chased by an adult conspecific female.
In L. phthirophagus the adult females attacked small cleaners more frequently when
they displayed the adult color pattern, indicating that juvenile coloration gives some
protection from conspecific aggression. Two other species oflabrids, Thalassoma
duperrey and Coris gaimard, showed the ability to shift back to juvenile coloration
when aggression was received from con specific adults, although the shift was not nearly
as rapid as seen in Labroides species.
Dascyllus albisella and Zebrasomajlavescens, common reef fishes, preferred to
solicit cleaning (by posing) from the adult-colored L. phthirophagus, indicating that
some hosts prefer the adult color pattern. Small L. phthirophagus shifted to adult
coloration more quickly when starved than when provided with host fish on which to
feed, indicating that the coloration shift is motivated by hunger. Even though juvenile coloration in some fishes may reduce the aggression
received from adults, in cleaner wrasses it also reduces food availability, making it
advantageous for them to shift to adult-coloration as soon as possible. Cleaner wrasses
have developed a quick, reversible coloration shift that allows changing to adult
coloration at a small size but allows reversing coloration if too much aggression is
received
