Despite looking like it is missing half of its
body, the ocean sunfish is the largest bony fish,
with a front-to-back length of 10 feet,
top-to-bottom height of 14 feet, and weight of
4,900 pounds being fairly common.
The ocean sunfish's leathery skin is almost
three inches thick on the ventral surface, and is
covered by a layer of denticles and mucus instead
of scales. Overall coloration ranges from brown
to silvery-grey or white, with a variety of
mottled skin patterns. This fish exhibits the
ability to vary skin coloration from light to
dark, especially when under attack.
The teeth in both the upper and lower jaws are
joined to form a single sharp-edged beak, making
it impossible for the ocean sunfish to completely
close its relatively small mouth. As it grows,
the caudal fin of the ocean sunfish is replaced
by a structure known as a clavus, which is used
more like a rudder than for propulsion. The
dorsal and anal fins are quite prominent. Adult
ocean fish do not possess a lateral line, and
only one gill opening is visible on each side,
which is located near the base of the small
Ocean sunfish are found in the temperate and
tropical regions of the Atlantic, Indian, and
Pacific Oceans, and in the Mediterranean Sea.
They are thought to migrate to higher latitudes
during the spring and summer months to pursue
their migrating zooplankton prey.
They prefer the open ocean but will
occasionally venture into kelp beds and deep
coral reefs in order to take advantage of the
"parasite removal services" offered by
reef-dwelling fish. Although they are often seen at or near the surface, ocean sunfish
are known to live and feed at depths of about 600
feet, and may go even deeper.
Jellyfish make up the bulk of
the ocean sunfish's diet, but it also feeds on
zooplankton, small crustaceans and fish, and even
Little is known about the breeding behaviors
of ocean sunfish. It is known, however, that it
begins life as a very small (about
1/10 inch) "normal looking" fish,
complete with full tail fin. As it grows the fish
becomes round and the body becomes covered with
spines (right). Those spines are
gradually lost until only 5 long ones are left,
which then shorten until being lost completely
and the adult body shape begins to appear. Based
on observations in marine aquariums, ocean
sunfish appear to go from larval to adult shape
in about 15 months.
Other Habits and
Ocean sunfish are usually seen
singly or in pairs, but may come together in
schools of a dozen or so at times. Those schools
most likely form when there is an abundance of
parasite-eating fish, and possibly when
zooplankton concentrations are high.
Not surprisingly, ocean sunfish are fairly
clumsy swimmers. They use their dorsal and anal
fins as their primary means of locomotion. They
flap these fins in a synchronous motion, which
also allows them to swim on their side, and by
waggling their dorsal and anal fins to move and
steering with their clavus.
Ocean sunfish have been seen diving below the
thermocline during the day, possibly to forage
for zooplankton that migrate vertically. They
have also been observed basking at the surface of
the water on their side, drifting with the ocean
current, which may be an attempt to re-warm core
body temperature after diving into colder water.
Ocean sunfish will also "fly out of the
water" to a height of 10 feet or so in the
air and then land with a great splash, an action
which is most likely undertaken as a way to get
rid of parasites.
genus & species Mola mola
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