Golden Trevally – Gnathanodon speciosus

Welcome back to the Findex, an in-depth look at the fish and coral life in the sea. Here we will take a look at the fish that everyone will see while they are diving but maybe don’t know much about or don’t get as much time in the spotlight as the big stuff! Let’s start with the Golden Trevally

Today’s fish can either be a beautiful background character or a huge sweeping shoal, depending on the age of the fish. While you will often photograph the juvenile stage by accident, the large shoals of the adults are also stunning.

The Golden Trevally, also known as the Golden Kingfish, Banded Trevally or the King Trevally, are large members of the Carangidae family. This is a huge family of fish including the jacks, pompanos, jack mackerels, scads and runners.

What’s in a name?

The Golden Trevally is named after the shiny golden colour that it shows as an adult and the bright yellow colour it shows as a juvenile. It is the only member of its genus, Gnathanodon, and gets its scientific name from both its mouth and its body. This trevally has no teeth, instead having big fleshy lips and swallowing its food whole. ‘Gnathos’ is Greek for jaw and the last part – made of ‘a’ and ‘odus’ means without teeth. Finally, ‘speciosus’ is Latin for beautiful and I think that speaks for itself.

Golden Trevally. Habitat and distribution.

Golden Trevally can be found pretty much anywhere throughout the Indo-Pacific region, from the Red Sea to Australia and over to the west coast of America and Mexico. They can be found on both coral reefs and open sand flats, wherever it can find food. It is however confined to inshore coastal habitats and rarely seen far from sandy areas. If you want to see these fish spawning, head to either the Persian Gulf or Hawaii. Hawaii hits its peak during late April to early September and the Persian Gulf kicks off in April and May.

Golden Trevally. Looks that kill.

As juvenile fish Golden Trevally are a bright lemon yellow with 6 thick black stripes along its body. These thick lines alternate with thinner lines in between them which serve as camouflage and to mimic other reef fish. The first stripe goes through the eye, which helps to hide the eye from predators. This can be seen in many reef fish and the idea behind it is to confuse predators as to which end of the fish is the head end. Predators want to attack the fish head on, as fish swim very quickly in one direction but not in others. If it can’t tell where the eyes are the predator might go for the wrong end, allowing the fish to escape. As the fish grows these black lines will fade slightly but can still be seen. The same happens to the yellow colouring, changing to a shiny gold colour on the face and fins. Watching the gold shimmer off a large shoal of these fish in the sunlight is simply beautiful.

Lifestyle choices of Golden Trevally.

Both male and female fish look very similar and it is very difficult to tell them apart from each other in water. They breed via broadcast spawning, which is where male and female fish release eggs and sperm into the water for them to mix and drift away on the current.

This takes place at night in time with the moon cycles, just before and just after the full moon. They grow to a maximum size of 120cm and can weight up to 15kg. Due to this large size and quick reproductive rate, they are often exploited by industrial fisheries and sport fishermen as well as being farmed for the aquarium trade.

Life on the reef.

You can often find juvenile fish sneaking into your photos because they live by mimicking Pilot fish. They swim following larger animals, such as sharks, mantas or groupers and pick up scraps of food left behind. They can also work as opportunistic cleaner fish, which means that they will clean other fish is they see something edible but it isn’t their sole life strategy.

This is also one of the reasons why the juvenile fish have such vivid black stripes, to mimic the look of the Pilot fish (Naucrates ductor). By following these larger animals, they are also protected from potential predators as most fish are unlikely to mess with sharks! Because of this, it means that juvenile fish have a wide range where they can be found around the reef.

Adult fish stop this lifestyle, choosing to keep to shoals around the sandy areas of the reef. They are carnivores and eat by extending their mouths into a long tube-like shape and taking a big bite of the sand. This is then filtered through their gill rakers, keeping all the bits they want before either spitting out the sand or expelling it through the gills. They will eat pretty much anything in the sand from crustaceans and molluscs to small fish. They are diurnal, which means they are active during the day and sleep at night.

Personal experiences.

I have had the pleasure of seeing these fish in both their juvenile and their adult life stages, both in the wild and in an aquarium environment. I have seen the juveniles swimming alongside rays in the Red Sea and Seychelles and cared for the adults in a public aquarium. In both stages they are fairly uninterested in divers, juvies hiding with their host and adults swimming slowly away from you. My colleagues, however, have seen plenty of the juveniles in the Maldives. In most of the photos, they take off the sharks, rays and other big stuff small shoals of Golden Trevally swim alongside them, adding a beautiful lemon yellow flash to the photos. Sometimes they are lucky enough to capture both trevallies and pilot fish, with the occasional fusilier or sergeant major to really fill out the picture with amazing colours.

The bottom line.

We travelled on the MV Emperor Orion doing the Best of the Maldives itinerary to see these fish. They can be seen year-round in this location as well as throughout the Indian and Pacific regions, the Red Sea and western American coast. Keep your eyes peeled when you are looking for the sharks, rays and pelagics as no doubt these little fish will be there too. The bright yellow of the Golden Trevally makes a really stunning addition to the blue and white patterns of a Whale shark!