The GT is robust and solid in appearance and can be recognised by a steep and blunt head profile.
They have immense power which can be attributed to thick shoulders and
midsections of muscle and large almost paddle like pectoral and tail fins.
Colouration can range from an almost white-silver to jet black. They may also exhibit a dusky golden hue all over the body, particularly on the fins. The GT lacks a dark spots/colouration on the Operculum (found behind the eye).
In addition to the body colour of the GT, striking striations and markings on the top section of the fish may also be present, particularly on the back. This is generally seen when the fish has a much darker back than the rest of the body, the contrasting markings showing up as light silvery lines. Black dots a few millimetres in diameter can also be found scattered all over the body, coverage can vary between none, sparse and widespread.
Scutes (small sharp plates) exist along the posterior portion of the lateral line and proceed along to the tail. Caution is recommend when holding a GT due to the sharp scutes which can inflict significant pain.
Left: Scutes along the tail. Right: Large pectoral fin.
GT distribution is widespread, existing in the warm
tropical waters of the Pacific and Indian Oceans. They are usually found as far south as central New South
Wales in Australia, east to the Hawaiian Islands, west to the eastern islands of
Africa and north to Japan.
Habitat ranges from estuaries to coral reef systems.
Juveniles tend to be more prevalent in estuaries and river systems. Larger
specimens move out to deeper water where there is usually structure such as a
coral reef, bombora or drop-off/channels. Strong currents are usually present
where these deepwater environments exist. They will also venture onto flats,
headlands and shallow water to hunt food. GTs can also be found along the reef
edge and points where large pounding swells crash on the reef and rock stirring
up food and creating the ideal environment to hunt.
GTs mature at around the ages of 3-4 years, they are generally around
60cm in length. This indicates that the GT is a very fast growing fish.
Large, usually solitary specimens can reach over 200lb and
be around 1.7 metres in length. In the author’s experience, major points and
structures in a reef system may be home to one large territorial specimen
(perhaps this is why they seem to be solitary?).
It is not known whether there is a ratio or abundance of what gender when it comes to larger more
dominant specimens
The GT uses its superior swimming abilities and power to hunt and smash baitfish. If the GT doesn’t engulf the prey within the first strike, the prey is usually stunned or dead from the strike impact. They will usually devour the prey quickly with one bite as competition can be fierce from other specimens in the pack.
Just about any baitfish (small fish) existing in tropical waters is in the GTs diet. Species of
Fusiliers from the Lutjanidae family seem to
be particular favourites of the GT. There have also been reports of juvenile Turtles & Dolphins being found within the stomach contents of larger GTs.
The author has also seen Tuna up to one metre in length being hunted on the surface by a large GT.
Large GTs can also be found in the presence of large reef sharks as they use the shark as a tool to ambush prey. Large GTs have also been known to eat other smaller GTs and reef fish when the smaller fish is hooked by an angler.
The only natural threats to the GT are species of tropical sharks and man.
Although not a commercial species in most Western countries, they are commonly commercially caught in 3rd world and island nations.
An angling technique known as ‘surface popping’ has already realised the value of the GT to recreational fishing. Most of these anglers are pro-actively engaging in catch & release, and careful fish handling practices. Some commercial operators who offer recreational fishing for this species have started to record and tag GT for scientific purposes.
Unfortunately, there are still Western countries that engage in
pointless killing of GTs. In some of these countries GTs are specifically targeted and killed as a trophy – the carcass is either sent to the taxidermy or disposed of as it is certain to contain a toxin known as Ciguatera which can
make humans very ill. Fortunately, with the surge of surface popping and promotion of catch and release, some of these GTs are being released in good, healthy condition.
It is the purpose of this site to educate people and help put an end to unnecessary and selfish killing of the GT.
Research Report: Behavioral ontogeny in larvae and early
juveniles of the Giant Trevally (Caranx ignobilis) (Pisces: Carangidae)
Authors:
Jeffrey M. Leis, Amanda C. Hay, Domine L. Clark, I-Shiung Chen, Kwang-Tsao
Shao
Abstract
"Behaviour of young (8−18 mm SL) Giant Trevally (Caranx Ignobilis), a
large coral reef associated predator, was observed in the laboratory and the
ocean. Size was a better predictor of swimming speed and endurance than was age.
Critical speed increased with size from 12 to 40 cm/s at 2.7 cm/s for each mm
increase in size. Mean scaled critical speed was 19 body lengths/s and was not
size related. Swimming speed in the ocean was 4 to 20 cm/s (about half of
critical speed) and varied among areas, but within each area, it increased at 2
cm/s for each mm increase in size. Swimming endurance in the laboratory
increased from 5 to 40 km at 5 km for each mm increase in size. Vertical
distribution changed onto-genetically: larvae swam shallower, but more variably,
and then deeper with growth. Two-thirds of individuals swam directionally with
no ontogenetic increase in orientation precision. Larvae swam offshore off open
coasts, but not in a bay. In situ observations of C. Ignobilis feeding,
interacting with pelagic animals, and reacting to reefs are reported."
General Information
