Giant Trevally (‘Ulua): 9 Fun Facts, Habitat, Diet, Behavior

The Giant Trevally, scientifically known as Caranx ignobilis, is a fascinating and powerful fish that reigns as the largest member of the Carangidae family. This impressive creature, commonly referred to as ‘Ulua in Hawaiian and GT in Australia, holds a special place in human culture. Its connection to ancient Hawaiian rituals and its economic significance in the fishing and tourism industries make the Giant Trevally an important and captivating species.

In this article, we’ll dive into the world of the Giant Trevally, exploring its appearance, habitat, and feeding habits.

9 Amazing Giant Trevally Fun Facts

1. Aerial hunting prowess: The Giant Trevally is known to exhibit incredible hunting skills by launching itself out of the water to catch its prey, sometimes even seabirds mid-flight. This aerial hunting technique is a rare and unconventional behavior among fish species.
2. Speed and strength: Giant Trevally is an extremely fast and powerful swimmer, capable of reaching speeds up to 50 km/h (31 mph). This speed allows them to chase and catch a variety of prey, including fish and cephalopods.
3. Monogamous relationships: Unlike many fish species, Giant Trevally form monogamous pairs during their breeding season. These pairs will stay together and protect their territory and eggs from other fish and predators, showcasing a unique level of commitment and cooperation among fish species.
4. Selective taste for prey: Giant Trevally are known to be selective in their choice of prey, often targeting specific species of fish and cephalopods. When hunting, they have been observed to pass up numerous potential prey items in favor of their preferred targets, demonstrating a unique level of discernment among fish species.
5. Nighttime hunting: While many fish species are more active during the day, Giant Trevally are known for their nocturnal hunting behavior. They use the cover of darkness to stealthily approach and ambush their prey, which often includes crustaceans and small fish.
6. Juvenile mimicry: Young Giant Trevally have been known to mimic floating debris or dead leaves to avoid detection by predators. This clever camouflage technique helps increase their chances of survival until they grow large enough to be less vulnerable to predation.
7. Age determination through otoliths: The age of a Giant Trevally can be determined by examining its otoliths, small calcium carbonate structures found within the fish’s inner ear. These otoliths develop rings, similar to tree rings, which can be counted to estimate the fish’s age accurately.
8. Cultural significance: The Giant Trevally holds cultural significance for indigenous people in the Indo-Pacific region, particularly in Hawaii, where it is known as “Ulua.” Ulua is considered a highly prized game fish and holds a special place in Hawaiian mythology and folklore.
9. Color-changing abilities: Giant Trevally can change their coloration depending on their environment and mood. They can display a range of colors from silver to dark grey, and can even exhibit a combination of colors, such as having a dark upper body while maintaining a silver underside. This ability helps them blend in with their surroundings and communicate with other individuals of their species.

Quick Overview of the Giant Trevally

Attribute	Information
Scientific Name	Caranx ignobilis
Kingdom	Animalia
Phylum	Chordata
Subphylum	Vertebrata
Class	Actinopterygii
Order	Perciformes
Family	Carangidae
Genus	Caranx
Species	C. ignobilis
Common Names	Giant Trevally, ‘Ulua (Hawaiian), GT (Australia)
Description & Appearance	Ovate, moderately compressed body, dorsal profile more convex than ventral, forked caudal fin, falcate pectoral fins, silvery color with dark spots, adult males may be black, small oval-shaped scaled patch centered on the body, blunt snout on deeply set head and body.
Size	Up to 5.5 feet and 200 lbs
Habitat	Tropical waters of Indo-Pacific region, rocky coral reefs, cliffs, coastal waters, estuaries, and rivers
Distribution	South Africa, Hawaii, Japan, Australia, and other regions in the Indo-Pacific
Diet	Predominantly feeds on fish; also eats crustaceans, cephalopods, and mollusks
Reproduction	Sexual maturity reached at 54-61cm and 3-4 years of age, spawning during warmer months, lunar cycles control spawning events, eggs are pelagic and transparent
Lifespan	20-25 years
Ecological Role	Top predator on the reef, important in controlling prey populations
Predators	Limited natural predators due to their size and predatory behavior; humans are their main threat
Conservation Status	No official conservation status but populations are declining due to overfishing
Economic Importance	Important for local economies in terms of tourism and the fishing industry; cultural connections in ancient Hawaii
Human Interaction	Fishing, risk of ciguatera poisoning when consumed, used in religious ceremonies in ancient Hawaii
Evolution	Not enough information available
Adaptations	Agile pack hunters, active during very dark nights, display aggressive behavior
Research & Discoveries	Continued study of population dynamics, feeding habits, and habitat use; hybridization with Caranx melampygus observed in Hawaii
Captivity & Aquarium Trade	Not commonly kept in aquariums due to their size and predatory nature
Status in Hawaii	Decline in numbers in Hawaii, heavy depletion in main Hawaiian Islands, banning of commercial take proposed
Fishing Techniques	Effective techniques include trolling, drifting, surf-casting; best baits include live fish, cut bait, and fresh octopus
Tackle and Lures	Stout spinning or conventional setup for poppers/stickbaits, use large poppers and stickbaits made by Heru, Halco, etc.
Best Locations for Fishing	Great Barrier Reef, New Caledonia, Indonesia, Fiji, Pacific atolls, Oman
Conservation Efforts	Volunteer angler tagging data, catch and release practices promoted by recreational fishing groups, proposals to reduce catch in Hawaii
IUCN Conservation Status	Least Concern (LC)
Landlocked Populations	In the Philippines, a population of giant trevally inhabit landlocked fresh waters
Hybridization	Hybridization with Caranx melampygus observed in Hawaii

Meet the Giant Trevally: A Force of Nature

Physical Features of the GT

The Giant Trevally boasts an ovate, moderately compressed body with a dorsal profile that is more convex than its ventral counterpart. Its forked caudal fin and falcate pectoral fins help it navigate the tropical seas with ease. This impressive fish can grow up to 5.5 feet in length and weigh a whopping 200 pounds!

Colors and Markings of a Mighty Predator

The Giant Trevally sports a silvery color with dark spots scattered across its body. Interestingly, adult males may turn black as they mature, adding to their imposing appearance. This coloration helps the Giant Trevally blend into its environment, making it a stealthy and effective predator.

Home is Where the Reef is: Habitat and Distribution

Where in the World is the Giant Trevally?

The Giant Trevally thrives in the warm, tropical waters of the Indo-Pacific region, which encompasses areas such as South Africa, Hawaii, Japan, Australia, and more. This extensive geographical range allows the Giant Trevally to make its presence known as a top predator in various ecosystems.

Preferred Environments of the GT

When it comes to choosing a home, the Giant Trevally favors rocky coral reefs, cliffs, and coastal waters. However, it’s not uncommon to find them in estuaries and rivers with low salinity levels. Juveniles, on the other hand, prefer turbid waters, which offer them protection from predators until they’re strong enough to fend for themselves.

A Hunger for Fish: Diet and Feeding Habits

The Main Course: Fish

The Giant Trevally is predominantly a piscivore, which means that fish make up the majority of its diet. Its impressive size and powerful body allow it to chase down and devour its prey with relative ease.

Additional Delicacies: Crustaceans, Cephalopods, and Mollusks

While fish may be the Giant Trevally’s preferred meal, it’s not opposed to snacking on other marine creatures such as crustaceans, cephalopods, and mollusks. This varied diet ensures that the Giant Trevally receives all the necessary nutrients to maintain its large, powerful body.

Hunting Strategies of the GT

Giant Trevallies are opportunistic hunters, meaning they will take advantage of any available food source. They have been observed employing novel hunting strategies, such as ambushing prey from behind coral structures or using their powerful bodies to create shockwaves that disorient their prey. Additionally, Giant Trevallies are agile pack hunters, working together to corral and capture their prey. This combination of stealth, power, and cooperation makes the Giant Trevally a formidable predator in the tropical seas.

The Circle of Life: Reproduction and Growth of the Giant Trevally

Reaching Maturity: Growing up GT

The journey to adulthood for the Giant Trevally is an impressive one. These powerful fish reach sexual maturity at a length of 54-61cm and an age of 3-4 years. Once they’ve matured, they’re ready to contribute to the next generation of Giant Trevallies.

Spawning Season: Love in the Tropics

The warmer months signal the beginning of the spawning season for the Giant Trevally. Interestingly, lunar cycles play a significant role in controlling spawning events, as they often coincide with full moons or new moons. This ensures that the Giant Trevally’s reproductive efforts are well-timed and efficient.

From Eggs to Giants: The GT Life Cycle

Giant Trevally eggs are pelagic and transparent, drifting through the ocean currents until they hatch. Once they’ve emerged from their eggs, the young Trevallies begin their journey to adulthood, growing into the powerful predators we know and admire.

Behavior and Ecology: The Social Life of the Giant Trevally

Going Solo: Maturing into Solitude

While juvenile Giant Trevallies may be found in schools, they become solitary as they mature. However, they will still come together for reproductive purposes and occasionally during feeding events.

Dawn and Dusk: The Giant Trevally’s Active Hours

The Giant Trevally is most active during the twilight hours of dawn and dusk, using these periods to hunt and feed. Additionally, they have been observed feeding during very dark nights, utilizing their keen senses to locate prey in low-light conditions.

Aggression and Power: The Giant Trevally’s Natural Instincts

The Giant Trevally is known to display aggressive behavior, especially when it feels threatened or cornered. Their powerful bodies and strong jaws make them a tough adversary when hooked by anglers. This characteristic has earned them a reputation as a challenging and rewarding catch for experienced fishermen.

Reeling in the Giants: Fishing Techniques and Tackle for the Giant Trevally

Tried and True Techniques: How to Hook a GT

When it comes to catching a Giant Trevally, there are several techniques that have proven effective. These include trolling, drifting, and surf-casting. Using topwater lures is another popular method, as it entices the predatory instincts of the Giant Trevally to strike.

Baiting the Beast: Lures and Baits for the GT

The Giant Trevally is not a picky eater, so a variety of baits and lures can be used to attract them. Live fish, cut bait, and fresh octopus are all excellent choices. When using lures, large poppers and stickbaits are recommended.

Tackling the Challenge: Gear for the Giant Trevally

To handle the strength and power of the Giant Trevally, anglers should opt for a stout spinning or conventional setup. A 100lb braided line and a 200lb monofilament or 100lb fluorocarbon leader are recommended to ensure that your gear can withstand the fight of the mighty GT.

Protecting the Giants: Conservation and Threats to the Giant Trevally

Declining Numbers: The Giant Trevally’s Struggle

Populations of the Giant Trevally have been experiencing a decline, particularly in Hawaii. Overfishing and habitat destruction have led to heavy depletion in the main Hawaiian Islands, raising concerns for the future of this iconic species.

Conservation Efforts: Fighting for the GT’s Survival

In response to the declining populations, various measures have been proposed to protect the Giant Trevally. These include banning commercial take and promoting catch and release practices among recreational fishing groups. By working together, we can help ensure the continued survival of this remarkable species.

Human Interaction and Economic Importance: Living Alongside the Giant Trevally

Fishing and Tourism: The GT’s Role in Local Economies

The Giant Trevally plays an important role in the fishing industry, where it is a popular game fish in many regions. Additionally, its reputation as a thrilling catch attracts tourists seeking fishing experiences, benefiting the economies of the areas where it is found.

Health Risks: Beware of Ciguatera Poisoning

While the Giant Trevally is an impressive and sought-after catch, consuming it can pose a health risk. Ciguatera poisoning, caused by toxins accumulated in the fish’s body, can result in severe and long-lasting symptoms in humans. Caution is advised when consuming Giant Trevally.

Cultural Significance: The Giant Trevally in Ancient Hawaii

Sacred Fish: ‘Ulua in Hawaiian Mythology

In ancient Hawaii, the Giant Trevally, or ‘Ulua, held great cultural significance. It was used in place of human sacrifice and featured in the Hawaiian creation chant. The Giant Trevally was also associated with the demigod Maui, who was believed to have fished up the Hawaiian islands.

Legendary Fishermen: Ku’ula and Ai’ai

The Giant Trevally is connected to the tale of Ku’ula and his son Ai’ai, the head fishermen of Hana in Hawaiian mythology. This connection further highlights the importance of the Giant Trevally in ancient Hawaiian culture and its enduring legacy in the tropical seas.

Frequently Asked Questions