Giant Trevally

The giant trevally (Caranx ignobilis) is a large, predatory species of fish ranging throughout the Indo-Pacific region. Alternate names for this fish include lowly or barrier trevally, giant kingfish, and ulua. It is infamous for being muscular and aggressive, which makes it a popular sport fish among anglers. Although its flesh is generally edible, some individuals are ciguatoxic and may cause illness in humans.

5 Giant Trevally Facts

• Extremely aggressive: These fish are so fierce that they occasionally ram sharks with their heads, injuring or even killing them. When curious, their instinct is to bite.
• Apex predators: Due to its size and aggressiveness, this species has few natural predators and will eat virtually anything it can catch.
• Clever hunters: They don’t just rely on their size and speed to catch prey. These fish are also infamous for ambushing prey, sometimes using other predators like sharks to intimidate smaller fish.
• Great jumpers: Despite their large size, these fish are capable of leaping out of the water. Some individuals use this ability to catch and eat birds near the surface.
• Fast swimmers: This species is quick on its feet (or fins) with a top speed of just over 37 miles per hour.

Evolution and History

A number of modern Perciform lineages had their beginning in the mid-Eocene Epoch, which took place 56 to 33.9 million years ago. The first fossils from the Caranx genus date back to this period. Scientists discovered most of them in the sedimentary deposits of shallow brackish or marine waters, primarily in the form of otoliths (inner ear structures).

One study found that there is limited gene flow between the two to three populations of Caranx ignobilis worldwide. These main populations are found in the central Pacific, western Indian Ocean, and western Pacific and eastern Indian oceans. The species bears similarities to Caranx melampygus, another predatory fish in the Indo-Pacific region.

The Swedish naturalist Peter Forsskål first described the giant trevally in 1775. He obtained the holotype from the Red Sea. Initially, taxonomists confused the giant trevally with the Atlantic crevalle jack, a superficially similar fish. However, scientists have discovered no phylogenetic relationship between the two fish to date.

French naturalist Bernard Germain de Lacépède first created this species’ genus Caranx in 1801. He initially intended it for the crevalle jack (Caranx carangua). The genus would go on to contain over 100 species, most of which scientists later determined were invalid junior synonyms. It also ended up absorbing a number of other genera. Today, the Gnathanodon genus is most closely related to Caranx. It contains only one species, the golden trevally (Gnathanodon speciosus), which was once part of Caranx.

Classification and Scientific Name

The scientific name for the giant trevally is Caranx ignobilis. Caranx comes from the French word carangue, which denotes a Caribbean fish. Ignobilis is Latin for “unknown,” “obscure,” or “ignoble.” Scientists classify this species as Osteichthyes, or jawed bony fish, which have skeletons primarily composed of bone instead of cartilage.

Scientists further group these fish into the class Actinopterygii (ray-finned fishes) and the order Perciformes (perch-like fish). This is the largest group of fish, comprising 41% of the world’s bony fish (over 6,000 species in approximately 150 families). Within this order, scientists place them in the Carangidae family, which includes over 200 species of jacks, jack mackerels, pompanos, scads, and runners. It contains about 30 genera, one of which is the genus Caranx. Besides Caranx ignobilis, this genus comprises approximately 18 species of jacks, trevallies, and kingfish. Taxonomists continue to debate over the inclusion of several other species.

Appearance

As its name suggests, the giant trevally is a large fish with an aggressive predatory streak. Its streamlined body is silvery-grey in color with a slightly darker head and dorsum. Males over 20 inches long are typically much darker, ranging from deep grey to black. This species’ gills feature gill rakers, which are small bony or cartilaginous protrusions that help strain tiny organisms from the water for food. Ventrally, the breast lacks scales, which resume just before the pelvic region.

This species has six types of fins: a spiny dorsal fin, a soft dorsal fin, a caudal fin, an anal fin, two pelvic fins, and two pectoral fins. Though their fins are typically grey to black, fish from murky coastal waters may have yellow fins, with the anal fin being the brightest.

This fish is the largest in its genus. Adult males of this species average 33 to 39 inches in length, though some individuals grow up to 67 inches long. The heaviest individual on record weighed just over 176 pounds, though adults may weigh as little as 28 pounds.

Distribution, Population, and Habitat

The giant trevally inhabits the Indo-Pacific region, an area encompassing the tropical Indian Ocean and the western and central Pacific Ocean, as well as the seas in between. Its range includes the Pacific islands as far as Hawaii, northern Australia, the eastern coast of Africa, and Japan.

Giant trevallies prefer warm, tropical, brackish waters at depths of 33 to 617 feet. These semi-pelagic fish often lurk around reefs, tidal flats, clear lagoons, and channels. Occasionally, they venture into estuaries. Older individuals tend to move farther offshore into deeper waters. This species is solitary except when mating or, more rarely, hunting.

Conservationists are unsure of this species’ population numbers worldwide. The IUCN lists them as Least Concern as of its latest assessment. However, there is evidence that their numbers are declining in Hawaii.

Predators and Prey

Giant trevallies are aggressive carnivores that hunt a variety of prey. They feed either individually or in schools, sometimes even hunting with trevallies of other species. They occasionally pick off prey escaping from other predators, like monk seals, or use sharks to ambush smaller fish. Because of their large size, they are an apex predator in most habitats.

These fish are diurnal, crepuscular, or nocturnal hunters depending on their location. For example, off the coast of South Africa, they tend to be diurnal or crepuscular, while they are mainly nocturnal around Zanzibar and Hong Kong.

What Do Giant Trevallies Eat?

These fish feed on whatever is easiest at the time, including crustaceans, cephalopods, mollusks, eels, and smaller fish. They are capable of leaping out of the water to catch birds. Larger individuals may even hunt other predators like tuna and mackerel. Juveniles eat smaller fish like young anchovies and sardines.

What Eats Giant Trevallies?

Sharks and humans are the primary threats to giant trevallies. However, these fish are so tough and aggressive that they sometimes ram sharks with their heads, causing serious or even fatal injuries.

Reproduction and Lifespan

Giant trevallies are mostly solitary except when mating. By three to four years of age, most individuals have reached a length of about 24 inches and are sexually mature. They prefer to spawn in the warmer months, though this is subject to location and lunar cycles. For example, fish off the coast of southern Africa spawn between July and March, peaking between November and March. In Hawaii, spawning takes place earlier in the year, between April and November. A peak occurs during May and August. Fish in the Philippines have a much shorter window, December to January, though they may experience a peak in July.

In preparation for spawning, males and females gather in schools of about 100 individuals among reefs, reef channels, or offshore banks. Several dark males chase one silver female; eventually, she and one of the males pair off and descend to the sea floor. Here, they release eggs and sperm. Though scientists are unsure of the exact number, researchers have observed captive females releasing thousands of eggs at a time. After mating, the two fish part ways. They may mate again with other individuals during the season.

The eggs are pelagic and hatch after approximately 28 hours to release free-floating larvae. These larvae drift for about a month until they grow large enough to swim against the current and hunt small organisms. They live to be up to 25 years of age, though most individuals do not make it past the larval or juvenile stages.

Fishing and Cooking

The giant trevally is a popular sport fish as well as an important commercial fish. In Hawaii, they have long held cultural significance, but their declining numbers have led to a drastic reduction in landings. Currently, the annual catch in Hawaii comes to approximately 10,000 pounds. In and around Asia, annual landings between 1997 and 2007 came to between 4,000 and 10,000 tons. Fisheries use hook and line, gillnets, handlines, and other traps to catch these fish.

Sport anglers value this fish because of its fighting spirit and impressive size. The best time to catch it is during the warmer months, which vary according to region. Both live and dead bait, as well as lures, are effective with this species. Squid, octopus, and various types of fish make excellent bait. The best lures are poppers and soft plastic lures, though anglers also use jigs, bibbed plugs, spoons, minnows, and saltwater flies.

Though they are good to eat, giant trevallies have a reputation for being somewhat oily. Their flesh is firm and dense with a relatively mild taste. Larger individuals tend to taste fishier. It’s important not to overcook the flesh as it can become rubbery. Common cooking methods include pan-frying, baking, and grilling. Try one of these recipes for oven-baked or pan-fried trevally fillets.

Unfortunately, some of these fish are ciguatoxic (containing toxins poisonous to humans) and have caused illness in consumers. Exercise discretion when choosing this fish as a dish.