not clearly known, although it has been suggested
that the anemone enjoys the physical stimulation provided by the
activities of the fish.
A particularly well-studied
symbiotic behavior is that exhibited by the cleaner fishes (p.
95). The cleaner fishes feed by picking parasites and
diseased or damaged tissue from the bodies of other fishes. This
is apparently so desirable to these other fishes that they will
come from considerable distances to the spot where a cleaner fish
is operating a “cleaning station” and wait patiently
with other parasite-infested fish for their turn. Although
the cleaner fish would presumably make a tasty snack for the fish
being cleaned, these larger fish do not eat the cleaner even when
it enters their mouths to remove parasites. The immunity
of the cleaner fish to predation by the parasitized host fishes
has allowed another species of fish, the cleaner mimic (p.
107), to enter the picture. This fish, although unrelated
to the cleaner fish, resembles it almost identically. An
unsuspecting fish, mistaking the cleaner mimic for the cleaner,
will allow the mimic to approach. The mimic does so, but
instead of removing the parasites, it bites a chunk out of the
surprised fish and then darts for cover.
Sex and reproduction
play an important role in the lives of fishes, and several groups
of fishes have adaptations relating to these activities. In
some species males and females have notably different appearances.
In the mahimahi (p.
49), the male’s head is higher and blunter than the female’s.
In other species, notably among the parrotfishes (p.
101) and the wrasses (p.
93), the adult male has a color pattern which differs from
that of the female and which is usually more elaborate and colorful.
Some species apparently
undergo sex reversal, beginning their adult lives as one sex and
then changing to the other sex under certain conditions. Clownfishes
(p. 83) usually
occur in pairs as adults, one male and one female (and the female
is usually somewhat larger than the male). If the male is
eaten by a predator, a small juvenile clownfish will mature and
become the new adult male. If the female is killed, the
adult male will change into a female and a juvenile will mature
as a male. In many wrasse species, the situation is reversed,
with the adult male being the larger of the two sexes. If
he dies, one of the females in his “harem” will change
into a male and become the new harem master.
Many reef fishes spawn
in large aggregations of males and females which come together
in particular places at particular times. Others spawn in
smaller groups, and some species form male and female pairs which
remain together for long periods of time. Most reef fish
species release their fertilized eggs freely into the water, where
they are carried offshore by currents. Hatching and early
development occurs offshore and it is not until the young reach
a certain size that they return to the reef to live. In
the case of the rabbitfishes (p.
117), the young return in large “runs” during certain
months of the year and at specific phases of the moon. The
returning young, known locally as manahac, are the basis of an
important seasonal fishery on Guam.