Latin name

Plectropomus leopardus

Other names

Common coral trout, leopard coral trout, blue-dotted coral grouper, spotted coral grouper.

Identification

The body is elongated and stout, with a standard length of 2.9-3.9 times the body depth. 

This species is characterised by the following features: thoracic rays 14-17 (usually 16), scales on lateral line 89-99, longitudinal row 112-127 scales, interorbital space without embedded scales, anterior part of jaw with a pair of large canines and lateral part of mandible with 1-4 large canines.

Features of fish fins

The dorsal fin contains 7-8 spines and 10-12 soft rays, while the anal fin contains 3 spines and 8 soft rays. The spiny part of the dorsal fin has a shorter base than the soft ray part. The caudal fin is pointed.

Fish colouring

The background colour is olive green to reddish brown or orange red, the upperparts are covered with evenly spaced bright blue patches and there is a blue ring around the eye which can be broken off. They can change colour quickly when hunting and are often spotted.

Distribution

Native to the western Pacific Ocean, where they range from southern Japan to Australia and from the east coast of Thailand and Malaysia eastwards to the Solomon Islands, the Caroline Islands and Fiji. In Australia, they are found on Beacon Island in Western Australia, Ashmore and Cartier Islands in the Timor Sea, along the tropical north coast as far north as Sydney. This range includes reefs in the Coral Sea, Christmas Island, the Cocos (Keeling) Islands and around Lord Howe Island in the Pacific. Islands and around Lord Howe Island in the Tasman Sea.

Habitat

A tropical marine species. They live on coral reefs at depths of 3 to 100 metres (9.8 to 328.1 feet).

Size

This species reaches a total length of 120 centimetres (47 inches), although they usually reach about 35 centimetres (14 inches), and the maximum published weight is 23.6 kilograms (52 pounds). Maximum reported age: 26 years.

Behavior

When the fish come together, the males establish temporary territories. They then perform elaborate courtship displays to lure females to their spawning grounds. As part of this ritual, males display the darkened edges of their fins, which can be turned on and off almost instantly. The male approaches the female, usually close to the bottom, by tilting his torso at an angle of 45-90° (almost lying on his side in the water), jerking his body several times and waving his head from side to side. He passes close to the head or torso of the female with the upper or lower part of his body. This process is repeated. After this courtship, if the female agrees, the spawning period begins. During spawning, the male and female swim quickly to the surface where, turning quickly, they release sperm and eggs into the water. The cloud of sperm and eggs released during spawning is not easily seen, but its presence can sometimes be detected by the feverish feeding of small fish feeding on zooplankton. Spawning usually occurs within 30-40 minutes of sunset. Some fish (especially males) spawn more than once during the evening.

Food and feeding habits

Predators. Juveniles feed mainly on crustaceans, especially prawns, that live on or near the bottom of the reef. Adults feed on a variety of reef fish. Pomacentridae, especially Acanthochromis polyacanthus, are most commonly eaten. Adults will also eat juveniles of their own species. 

Individuals usually feed once every 1-3 days, although they may go without food for many days. Approximately 90% of the food consumed is digested within 24 hours. This species feeds only during daylight hours, most commonly at dusk and dawn. It hunts from ambush, sneaking up on fish that live among the corals at the bottom of the reef. The Leopard Coral Grouper hides and remains very still and alert, ready to attack passing prey. The crouching method is used to hunt gregarious fish higher up in the water. In this case the grouper slowly approaches the prey and attacks it at high speed. 

Reproduction

They are primordial hermaphrodites, beginning life as females and changing sex later in life. The reason for this sex change is unknown. On average, the sex change occurs when the fish reach a length of 23 to 62 centimetres (9.1 to 24.4 inches); the average length at sex change is 42 centimetres (17 inches). This is thought to occur most frequently in the first few months after spawning. Small fish tend to be female, while most large fish are male.

The spawning season corresponds to an increase in water temperature (from 25.0 to 26.5°C or 77.0 to 79.7°F) in late spring. In the northern part of the Great Barrier Reef, these fish spawn from September to December, while in the southern regions, where the water is cooler, spawning occurs from October to February. The start and end of spawning can vary from year to year due to changes in water temperature. Fish tend to gather in dense groups to spawn. These aggregations form around reef slopes at depths of 10 to 15 metres (33 to 49 feet) and peak around the new moon. Spawning occurs at high tide, particularly during low tide. This is thought to allow the newly released eggs to move away from the reef and associated predators. Spawning usually takes place at dusk, when insufficient light makes it difficult for predators to see and eat the eggs.

Life cycle

Like most reef fishes, it undergoes a larval stage in which eggs and larvae develop in the water column and disperse to nearby reefs. Fertilisation occurs after spawning; fertilised eggs float just below the surface. The incubation period of the eggs is unknown, but may range from 20 to 45 hours (incubation period in related species). The newly hatched larvae are not well developed and receive nutrients from the yolk sac. As they develop, they form spines, fins, intestines and other internal organs, as well as sensory organs. Eventually the yolk sac is completely absorbed and the larvae begin to see and catch their own prey.

The fastest period of growth is during the first three years of life. The average daily growth rate of newly settled juveniles is 0.81 mm per day. This means that they reach almost 14 cm in the first 6 months. Growth rates vary; each age class is characterised by a wide range of sizes. To estimate growth, the age and size of the fish must be determined. 

Fishing

A popular commercial fish in all fisheries due to its high market prices in markets around the world. It is sold as both live and chilled reef fish, mainly in Hong Kong. Catching live fish for export is an important commercial fishery in the Asia-Pacific region, currently mainly in Indonesia and the Philippines. In Australia, it is caught in commercial fisheries using hook and line, while recreational anglers use lines, rods and underwater guns. In the Philippines and Indonesia it is fished with cyanide. In Fiji and New Caledonia, it is caught by artisanal fishermen using hook, line and spear and as bycatch in traps.

Relationship with a person

Highly prized as a food fish. The flesh of large individuals may contain very high levels of ciguatoxin.