Why so blue, Jack?
Jackfish, also known as Bluefin trevally or blue jack, are one of the most common fish patrolling the reef slopes over coastal and oceanic reefs. These fish are easily distinguished by their electric blue fins, which can be absolutely mesmerising to see when they catch the sun. They are stunning and captivating to witness underwater, not only because of their fins, but also because their body is a brassy color which becomes lighter, fading to silvery-white on the stomach.
The Bluefin trevally is a strong predator that displays a wide range of hunting techniques- from aggressive midwater attacks to reef ambushes, even foraging by interacting with other larger species. You can find them in schools or swimming around alone, hunting for smaller fish, crustaceans, squid and octopus. The larger jacks go after the brightly colored fusiliers in a high-speed chase that is thrilling and exciting to watch as you relax in the water. They are extremely agile and swim fast, covering great distances. The adults are commonly found in the drop offs with a strong current and use one of their many hunting techniques to capture their prey, sometimes even hunting in a shoal.
The larger jacks prey on the likes of parrotfish, bigeyes, mullets etc. whereas the little jacks mostly go after small prawns, shrimps and other crustaceans that they filter from the water. Just because they are vivacious predators doesn’t make them resistant to other, bigger predators. Dolphins and large tuna find the jack fish to be quite palatable, and are some of the top jackfish predators.
Unfortunately, jacks are also highly sought after as game fish or food. Commercial and recreational fishermen like to go after these fish as their meat is one of the favourites of the locals. It is also a highly preferred gamefish, second to its cousin, the Giant Trevally. Rapid decline in the population has led to extensive aquaculture trials and an imposed fishing limit to prevent further exploitation.
The Bluefin jack is definitely a fish to look out for during a dive, to appreciate its beauty and agility and to capture the shimmer of its scales as it passes by.
Written by Smrutica Jithendranath
Photos by Janez Kranjc & Ivana O.K
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