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CARTILAGINOUS FISHES (Chondrichthyes)
All sharks and rays belong to the class of cartilaginous fishes.
Their skeleton is built of hardened cartilage, as opposed to bone.
The body muscles are joined to the spine by connective tissues.
All cartilaginous fishes are carnivores. They have electro-sensitive
pores on their head to track down their prey. Cartilaginous fishes
reproduce partly oviparous, partly viviparous. Unlike bony fishes,
fertilization of the eggs happens inside the females. Compared with
bony fishes, cartilaginous fishes reproduce slowly with long gestation
periods (viviparous), or with only a small quantity of eggs (oviparous).
Many species of cartilaginous fishes, in particular sharks, are
endangered. Every year, tens of millions die in floating nets and
in the commercial hunt for shark fins. The shark fin soup industry
is perhaps the sharks biggest enemy, and unless consumers become
educated, many species of shark may soon be extinct.
Sharks
| | LEOPARD SHARK (Stegastoma fasciatum)
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 Length:
to 3 m
An unmistakable shark, frequently encountered in coral reefs
and lagoons. Its caudal fin is almost as long as its body.
Often called a Zebra shark. During the day the Leopard shark
is usually seen resting motionless on the bottom. During the
night the nocturnal hunter swims around to find its prey of
crustaceans, shelled invertebrates and small fishes. Most
frequently seen shark at all dive sites in the Andaman Sea.
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| | WHALE SHARK (Rhincodon typus)
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 Length:
to 18 m
The largest fish in the ocean, this giant is easily recognized
by its immense size and a two-tone pattern of light spots
and lines on a dark brown dorsal surface. The enormous mouth
can be opened very wide to filter large amounts of water for
small fish and plankton. Whale sharks are viviparous. Their
hatchlings are about 70 cm long at birth. Only very little
is known about the habits of Whale sharks. Recently, they
have come under severe hunting pressure for their fins. Whale
sharks are one of the top attractions in the Andaman Sea from
November to April.
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| | TAWNY NURSE SHARK (Nebrius ferrugineus)
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Length: to 3 m
Nocturnal, resting in caves or large ledges in daytime, often
in groups. Only occasionally moving about during the day.
A large, sluggish species with nasal barbels to track down
prey. Feeds primarily on cephalopods, sea urchins and fish. |
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| | BLACKTIP REEF SHARK (Carcharhinus melanopterus)
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Length: to 2 m
Usually seen in small groups on reef tops, hunting for fish.
It readily enters very shallow and even brackish waters. The
species is easily identified by its distinct fin tips, which
often protrude from the shallow water. |
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| | WHITE-TIP REEF SHARK (Triaenodon obesus)
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 Length:
to 2 m
Likely the first shark encountered on reefs around the Similans.
The common species is seen singly or in small groups in the
reef, resting on the bottom or in caves by day, hunting fish
among the corals at night.
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| | GREY REEF SHARK (Carcharhinus amblyrhynchos)
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 Length:
to 2 m
One of the most popular sharks in general. Grey reef sharks
are curious and readily approach divers, sometimes showing
territorial behavior: hunching the body, lowering the pectoral
fins and swimming in an exaggerated manner. They feed on bony
fishes mainly between dusk and dawn.
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RAYS
| | KUHLS STINGRAY (Dasyatis kuhlii)
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 Width:
to 40 cm
Widespread species, living on vast sand flats, by day often
buried in the sand. It has a caudal fin fold, and usually
two stings set midway on the tail. Tip of tail distinct. Often
mistaken as Blue spotted Ribbontail (Taeniura lymma).
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| | BLOTCHED FANTAIL RAY (Taeniura meyeni)
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Width: to 2 m
Most common stingray species in our area. The species is encountered
along the base of drop-offs or on sand flats in or near coral
reefs. By blowing into the substrate, the ray dislodges mollusks
and crustaceans from the sand, which are taken up and eaten.
Not being shy, this large ray is a good photographic model. |
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| | SPOTTED EAGLE RAY (Aetobatus narinari)
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Width: to 3 m
This species is easy to recognize with its dark dorsal surface,
which carries small white spots, and a striking head. It is
found mainly in open water of coastal coral reef areas as
well as around atolls. Mainly encountered singly or in small
groups. Their favorite prey is shelled mollusks, which they
crack open between two flat dental plates consisting of interlocked
rows of crushing teeth. |
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| | MANTA RAY (Manta birostris)
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 Width:
to 7 m
The largest ray lives pelagically in the open sea, but is
also observed near reefs at cleaning-stations to allow cleaner
wrasses to remove skin parasites and old skin. The huge Manta
ray is a filter feeder, like the whale shark. It feeds on
plankton and small fish. The prey is guided into the enormous
mouth by a fleshy lobe on each side of the head. Manta rays
feed close to the surface, where plankton tends to accumulate.
In the process, the rays execute somersaults and even break
the surface. They can sometimes be observed jumping high out
of the water. What may appear to be playing is usually a form
of dominant behavior, or an attempt to shed dermal parasites.
Manta rays are viviparous and usually give birth to two young
after a gestation period of thirteen months.
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SPOTTED SHOVELNOSE RAY (Rhynchobatus djiddensis)
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Length: to 3,10 m
This fascinating fish is a bridge of sorts between the evolution
of sharks and rays. The species lives on sand or coral rubble
down to 50 m, and is sometimes seen in extremely shallow water.
They are viviparous with a litter size of about four. They
mainly feed on crustaceans and other shelled invertebrates. |
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