Anthias (Anthinae)
Anthias , much smaller than their grouper relatives, also play an important role in the reef community. Anthias in particular are very abundant in terms of number of individuals and often form huge mid water feeding aggregations, especially adjacent to steep outer reef drop-offs, like when yo are diving around the Gili Islands Halik Reef.
Description
All twenty-five species of trevally have elongated, compressed bodies and deeply forked caudal fins, with long, sickle shaped pectoral fins. The Giant Trevally (also known as the ulua, ronin jack and “GT”) is the most prized of the species by anglers and is identifiable by an ovoid patch of small scales located on the breast ahead of the ventral fins. Coloration for the Giant Trevally can range from silvery-white to almost jet-black.
The Giant Trevally uses its superior swimming abilities and power to hunt and smash baitfish. The Giant Treavally is known for stunning prey with its first strike and then circling back to engulf the wounded and/or disoriented baitfish. They will usually devour the prey quickly with one bite, as competition can be fierce from other members of the pack. As they grow, larger specimens move to deeper water and congregate over coral reefs and other underwater structure. Giant Trevally also venture onto flats, headlands and shallow water to hunt food. Giant Trevallies can be found along the reef edge and points where large pounding swells crash on the reef and rocks stirring up food and creating the ideal environment to hunt.
Pound for pound, these are among the hardest-fighting fish in the sea. The current record comes from a plug cast from shore in Japan. Fishing for trevally is best in hotspots like the Seychelles and the edge of the outside reef at Christmas Island, which is also a world-class bonefishing destination.
Average Length
23 inches – 5 feet
Average Weight
30 – 60 lbs
Habitat
The Giant Trevally ranges from estuaries to coral reefs. Juvenile fish are prevalent in estuaries and river systems.
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Range
Distribution is widespread. They’re found in the warm tropical waters of the Pacific and Indian Oceans as far south as New South Wales in Australia, east to the Hawaiian Islands, west to the eastern islands of Africa and north to Japan. You will find Giant trevallies on the dive sites around the Gili Islands. Specially Deep Turbo, Halik and Sharkpoint are famous for seeing the trevallies.
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Porcelain crab
Neopetrolisthes maculatus
These delicately spotted crabs live in a symbiotic relationship with anemones. They keep the anemone clean while benefiting from its protection. Porcelain crabs have modified mouthparts which open out like fans into the oncoming current in order to trap tiny particles of plankton
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Life span
They live for around 2-3 years.
Statistics
They are less than 24mm in width.
Distribution
They are found in the Indo-Pacific. You see them when you are diving around the Gili Islands Indonesia.
Habitat
They are also known as anemone crabs, due to their close association with anemones. Porcelain crabs may be found singly or in pairs, hidden between the stinging tentacles, or near the mouth, of anemones. They are found in reef habitats, to depths of around 10m.
Diet
They are mainly plankton feeders, sieving tiny particles from the water column using their fan-like mouthparts. They also eat mucus from the anemone.
Behaviour
Porcelain crabs are relatively aggressive, using their large claws to deter invaders, including anemone fish. Although both use an anemone host, porcelain crabs and anemone fish are not commonly found together, the crab usually losing out to the tougher fish. Like anemone fish, porcelain crabs are immune to the anemone’s stinging tentacles. It is a mutualistic relationship, since both parties benefit from the arrangement: the crab gaining safety and shelter, in return for cleaning.
Reproduction
Porcelain crabs are often found in heterosexual pairs. They have internal fertilization, the male passing sperm to the female in the form of a tiny packet called a spermatophore. The eggs are carried by the female in a brood flap, on the abdomen. A single female may carry nearly 1,600 eggs at a time. The larvae are planktonic for several weeks before settling.
Conservation status
Porcelain crabs are not of the IUCN Red List, but suffer from habitat loss if reefs are damaged or polluted.
TRUMPETFISH (Aulostomus chinensis)
Also known as Trumpet, Atlantic Trumpetfish, Caribbean Trumpetfish, Trumpeter and Painted Flutemouth. You can find them everywhere around the Gili Islands when you are snorkeling or divinvg.
The Trumpetfish can be recognised by its long body, tubular snout with minute teeth, its chin barbel and the series of short dorsal spines.Their bodies are inflexible, supported by interwoven struts of bone. The colouration of this species is variable. It is often brown or green with pale stripes and bars, and white spots posteriorly. A yellow colour variety is common in some areas. Individual fish have the ability to change their colours very quickly. Trumpetfish have the capability to rapidly expand their jaws into a circular gaping hole almost the diameter of their body when feeding.
The trumpetfish is the true master-hunter on the coral reef. Yes, this fish looks rather benign and yes it is a relative of the passive sea horses, but it is truly a fish-killing machine! The trumpetfish employ a variety of strategies to capture their fish neighbors. One of the most spectacular is referred to by fish behaviorists as “hunting by riding” (a.k.a. shadow stalking). This is where the trumpetfish uses another fish as a blind to sneak-up on its unsuspecting quarry. The hunter-extraordinaire will lie along the back of the larger fish as the latter swims over the reef. The species that the trumpetfish uses as a blind are usually large herbivores (e.g., parrotfishes) or omnivores (e.g., angelfishes). Because these species don’t cause small fish to flee (because they do not feed on them), the trumpetfish can hide behind them to get close. Once the distance between predator and its prey reaches a critical point, the trumpetfish will dart out from its living blind like an amphibious arrow! While it may look like the trumpetfish has a relatively small mouth, the floor of the narrow snout is very expandable, which enables it to distend so larger prey can pass into the stomach. If you see a trumpetfish while diving, stay back and watch it for a while. There is a good chance you will see it engage in this fascinating hunting behavior.