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TREVALLY (JACK) - CARANGIDAE
The Carangidae family are one of approximately two hundred different species. These big silvery predators are fast swimmers and can reach speeds of fifty Km p/h. They are mostly found in open water but can often be seen patrolling the reefs looking for food. The bigeye trevally (Caranx- sexfasciatus) are mostly seen in plankton-rich waters where they swim around in big schools of more than hundred fish. They swim in circles and because of the amount of fish in a school, can often create a huge cylindrical funnel where divers can sometimes swim through. Trevallies are constantly on the move and are active both day and night. They are missing, or only have a small swim bladder, so have to keep on moving, or they will sink. Some species feed on reef fish, shells and crustaceans while others feed on schooling fish. Working from different sides and at high speed they will penetrate a school of fish and catch what they can. Trevallies have small teeth and are able to hold fish into their mouth, but cannot bite it into pieces. This is the reason they have to swallow their prey whole. All trevally species mate and spawn in open water as the eggs will not have predators. Some juveniles grow up between seagrass or floating weeds, while the young from Alectis indicus and A. ciliatus grow up pelagic. They have very long fin-filaments of more than a meter which can make them look like jellyfish. This can be a way of protection but also handy for catching prey. The most common juvenile is the striped golden trevally (Gnatodon speciosus) that accompanies big jellyfish, Oceanic whitetip or leopard sharks, big groupers and whalesharks. The reason why they are often seen with sharks is because they use the shark’s rough skin to get rid of their parasites by rubbing themselves against them.
- Check the sub-map for the specimen information files -