August  2003
 
 
 
 
 
 

The Manta Ray

Order                      Family                     Genus and Species

Rajiformes                    Mobulidae                         Manta birostris

The largest and most fearsome-looking of all the rays is the giant manta, also called the
devilfish, which inhabits the temperate zones of the world's oceans.  Although this huge
sea creature appears dangerous, it is one of the least aggressive of the ray family and
subsists mainly on plankton, the collection of small or microscopic organisms, including
algae and protozoans, that float or drift in great numbers in fresh or salt water, especially
near the surface, and serve as food for fish and other larger organisms.

Mantas rest on the ocean floor, or seabed, and settle themselves out with their pectoral
fins outstretched to their full length.  These fins often grow to a combined distance of
20 to 25 feet and present a menacing presence when seen by fishermen or by deep sea
divers.  These mantas move through the water by flapping their fins in a bird-like up and
down motion and often will hold their fins outright and glide through the water, much as
an eagle soars through the sky.

The manta pictured above has a couple of remoras (small scavenger fish) attached to its
stomach area.  These fish suction on to the mantas and hitch a ride to the next feeding
grounds where they feed on plankton and other small organisms stirred up by the flapping
of the mantas giant pectoral fins.  It is not unusual to see a dozen or more remoras either
attached to the manta or trailing close behind.

Although the manta often reaches a weight of over 3,000 lbs, they sometimes indulge in a
series of spectacular leaps which propel them as high as 15 feet out of the water.  They
crash back to the oceans surface with such force that the loud splashing sound can often
be heard for miles on a still sea.   It is not known for sure why they put on this acrobatic
display but there are several theories.  One theory is that the leaping and crashing may be
a show of territorial supremacy and that this and a large area surrounding his leaps are,
therefore, marked as his domain.  Another theory is that the manta is trying to rid itself of
the sea lice which infest its skin and cause irritation.  Either, neither or both of these
explanations may be true, but regardless of the reason, the leaping display is exciting to
witness.

Above is a male manta, seen from underneath, as it cruises through the seas searching
for food.  The manta feeds by opening its huge mouth and swimming into a drifting mass
of small shrimp-like animals, plankton, seaweed, and other small organisms. As water
passes through its gills, the food items are strained out and swallowed.  The manta will
sometimes make numerous backward loops through the plankton, scooping up large
amounts of edible debris with each loop.

Mantas sometimes reach a length of 20 feet, including the tail, but the average length is
around 16 to 18 feet.  These fish mate all year long and , unlike most fish, reproduce by
physical union.  Copulation is achieved by a serpentine lateral curvature of the spine with
the male alternately advancing one of his claspers ( male sexual organs) while withdrawing
the other.  Mantas are sometimes born during the female's leaps into the air and make their
entry into the world in a spectacular fashion.  It is not known how long these unusual fish
live.

The manta in the above graphic is being shadowed by his usual entourage of remora and
has his pectoral fins fully extended as he glides through the ocean.  His cephalic fins, the fins
that are pointed downward in this graphic, are used to funnel food into his mouth; the manta's
eyes are located at the base of these fins.

Mantas are related to sharks and skates and have a skeleton made up of cartilaginous gristle.
Although true bone is not entirely absent, it is confined to dentine in the teeth, skin denticles,
and spines.  The large, thick fins of cartilaginous fish are different from bony fish, in that they
are stiffened internally by struts of cartilage at their base and hundreds of filamentous rods
located peripherally.  The pectoral fin skeleton attaches to a strong pelvic girdle which then
supports the pelvic fins and is embedded in the ventral ( lower surface) layers of body muscle.

The stingray, pictured above, is a close relative of the manta ray and is one of the more
dangerous members of the ray family.  This particular ray has several specialized venom
producing cells located in the spine.  Whenever the stingray is disturbed or threatened, it
arcs it's spine and uses it's muscular tail to drive the spine against and into the victim's
body.  Teethlike serrations tear tissue and facilitate the spread of venom.  Although this
venom is seldom fatal, searing pain and swelling will definitely send it's human victims off
to the doctors office.

Manta rays and their relatives can be found in the area shaded blue in the graphic
located below.

Check back next month for September's "Creature of the Month"....The Nile Crocodile

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