Diving Indonesia Periplus Adventure Guid. David Pickell
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Gill structure—elasmobranch means "plate-gilled"— and other physical features differ between bony fish and sharks and rays, which are considered a more primitive form.
Sharks. There are many species of sharks in Indonesian waters, but those most commonly seen by divers are the reef white-tip shark (Triaenodon obesus), the gray reef shark (Carcharhinus amblyrhynchos), and the reef black-tip shark (C. melanopterus).
The reef white-tip shark grows to 1.7 meters, and is a thin, gray fish with white tips to its dorsal and tail fins. This is the most commonly seen shark on the Indonesian reefs. This small shark can be often be found hiding under overhangs.
The gray reef shark grows up to 2.3 meters, and has a very dark trailing edge to its tail. Although this animal is known to be aggressive in some areas, it is not considered dangerous in Indonesia.
The reef black-tip shark grows to 1.8 meters, and is pale gray or brown with distinct black tips on all its fins. This shark sometimes comes up into very shallow water on reef fiats and in lagoons to look for food.
The largest fish extant is the whale shark (Rhincodon typus), a harmless animal that strains krill and small fish from the water. Growing to more than 12 meters in length (although specimens of 5-7 meters are more common), the whale shark is not a reef fish, although it can be found seasonally off some reefs in Indonesia.
The only really dangerous sharks a diver might encounter on an Indonesian reef are the tiger shark (Galeocerdo cuvieri), a large—up to 5.5 meters—scavenger that sometimes comes up onto the reefs at night or in the late afternoon/These sharks, however, are very rarely seen.
Rays. Structurally, rays are essentially flattened sharks. The stingrays have one or two stout spines at the base of their tail, which are their main means of defence. They will not normally be used against divers, although you should always take care to avoid stingrays while walking in shallow water.
Stingrays are bottomfish, and have strong teeth which they use to crush shellfish. In areas where stingrays are common you may see large craters in the bottom, caused by their feeding activities. Perhaps the most common stingrays in Indonesia are two species of blue-spotted stingray: Taeniura lymma, which frequents coral rich areas, and Dasyatis kuhlii, which lives in sandy areas of disturbed reef, or between patch reefs. A much larger animal is the grey reef ray (Taeniura melanospilos).
Not all rays are bottom-dwellers. The spotted eagle ray (Aetobatis narinari) cruises the reef edge looking for crustaceans. Eagle rays can reach 2.3 meters across.
The largest ray, however, is the manta (Manta birostris). Like the whale shark, mantas are essentially open water fish, but they are regularly seen by divers in Indonesia. The manta ray, growing up to 6.7 meters across and weighing 1,400 kilos, is a planktivore. Both whale sharks and mantas occur only seasonally in different parts of the country, as they migrate to the areas where the plankton is thickest.
Because they are found in areas dense with plankton, mantas tend to be seen at times when visibility is relatively low. This, however, is a small inconvenience when weighed against the pleasure of swimming with such magnificent creatures.
Sometimes seen in the same places that attract mantas are the smaller, but very similar devil rays (Mobula). These animals travel in groups and sometimes large schools.
Bony Fishes
Eels. The moray eels (family Muraenidae) are common both in folklore and on the Indonesian reef. Although not as dangerous as Hollywood would have us believe, they have sharp teeth and should not be provoked. The largest species, the giant moray (Gymnothorax javanicus), can reach more than two meters in length, and weigh 35 kilos. Many morays are nocturnal hunters, resting in holes by day and prowling the reef by night. They feed on dozing fish which they detect by smell.
The ornate ghost pipefish, Solenostomus paradoxus. This strange animal is a relative of the seahorses and pipefishes, however in Solenostomus the female broods the eggs. The coloration and growths are cryptic. This juvenile stands out here against the brilliant red crinoids, only because it has moved from a neighboring white crinoid or antipatharian. Tulamben, Bali.
A school of shrimpfishes, Centriscus scutatus. The shrimpfishes always swim with their noses pointed downward, in the process of evolution their dorsal, tail and anal fins have migrated to a position on the side fo the body, where they can produce lateral motion while the animal is oriented vertically,
A very beautiful eel, related to the morays but more delicately built, is the blue ribbon eel (Rhinomuraena quaesita). The adult coloration of this animal is electric blue and yellow, and adult females turn bright yellow. Juveniles are black.
Several species of the unusual garden eels (a subfamily of the conger eels) can be found on sandy bottoms in Indonesia. They live in burrows in often large groups, and the sight of all their thin bodies waving in the current gives them their common name. They have small mouths, and pluck plankton from the current. If you swim over the "garden" the eels will slip back down into their burrows, disappearing in a wave before you.
Although garden eels are usually found in deeper water, particularly the sandy channels between reefs, they can sometimes be seen in very shallow Sand patches on the reef. There is a colony of garden eels in shallow water on the approach to the popular wreck at Tulamben, Bali.
Seahorses and pipefish. These fishes (family Syngnathidae) are generally slow-moving and secretive, and are not often easy to find. They are planktivores, and can be found in sea grass beds and estuaries as well as in coral reefs. In tact; their fins are poorly developed, and they shun areas of high current or surge. Seahorses (Hippocampus) can be highly camouflaged, some exactly matching a single species of gorgonian.
The master of camouflage, however, is the ghost pipefish (Solenostomus cyanopterus), an animal whose shape and color precisely duplicate a blade of turtlegrass, A strikingly colored relative is the ornate ghost pipefish, S. paradoxus.
Pipefish are long and thin, and superficially appear quite different from seahorses. In fact, structurally they are quite similar, the pipefish just being a stretched-out version. The male incubates the eggs in a pouch on its stomach, and the young are born "live."
The large trumpetfish (Aulostomus chinensis) looks like a pipefish on steroids (these can be a half-meter or longer) and feeds on small fish. It has the curious habit of hiding behind larger fishes until it comes within range of its prey. One color morph is bright yellow.
Scorpionfish. The most commonly seen of this family (Scorpaenidae) are the lionfishes (Pterois and Dendrochirus). During the day these lavishly colored fish can be seen perching on coral heads. Perhaps because of their poisonous fin rays, they are relatively unperturbed by the presence of divers.
Lionfishes feed mainly at night on shrimps and small fishes. They use their elaborate fins to shepherd their prey into a suitable position, whereupon they shoot forward and inhale it whole into their large mouths.
Scorpionfish are less commonly seen, chiefly because they are so well camouflagued. Covered with folds and flaps of skin, they blend right in with the algae and other growths.
The scorpionfishes and lion-fishes have a row of poisonous spines along their backs. So, despite their usually benign behavior these fish should be treated with some respect. More than one underwater photographer has been stuck by a lionfish while trying to encourage it into position for that perfect photograph. Lionfish poison is not strong enough to kill an adult, but it will certainly give you many hours of acute pain.
Some victims have required hospitalization. The best treatment is to immerse the affected part in very hot water, as heat breaks down the venom.
Much more dangerous is the stonefish (Synanceia verrucosa), which carries a toxin responsible for several well-publicized deaths. These animals are masters of disguise, and encrusting algae and bryozoans actually grow onto their skin. When a small fish or crustacean