405_April_24

MARINE BIOLOGY WITH MIKE SCOTLAND - FISH IDENTIFICATION

The very common Red lined Triggerfish, Balistapus undulatus .

Titan Triggerfish are extremely common in most parts of the Great Barrier Reef and across the whole Pacific These are one of the largest and most powerful, growing up to half a metre. They have developed a habit of water blasting the sand to reveal food items such as worms, crabs and sea shells to eat. They also move small rocks with their powerful jaws. As a result, some wrasse follow them to sneak in and steal anything edible that gets uncovered as the sand is disturbed.

During the mating season, males set up territories and water blast a sandy hollow for the female to lays several thousand eggs into. These sandy hollows can be up to five metres across and half a metre deep. Both male and female guard the eggs. There is a high mortality rate and most of the eggs get eaten. The fish larvae are planktonic and drift off into the blue beyond. The very beautiful deep blue Red Tooth Triggerfish is unusual in that it is a plankton plucker. It lives on steep reefs and spends a lot of time in the open water feeding. They live in large groups. As you approach, they retire to a crevice in the reef but like many fish they have immense curiousity. Another very beautiful species is the Clown Triggerfish, Balastoides conspicillum . Many people are hypnotised by their striking colours. Clown trigger fish loved to death literally by aquarists, over collected from the wild and are therefore uncommon. The juveniles are much brighter in colour. As they mature they develop large white spots on the lower half of their body. I have compared Clown Triggerfish from Thailand, Fiji and the Great Barrier Reef. I studied them closely to try to identify any subtle differences in colour patterns. Sydney divers can see tiny Half Moon Triggerfish during summer and Autumn. They drift down from Queensland in the Great Eastern Australia current and are only found in the warm shallow water. They do not survive the cooler months. On the point of looking closer at fish, one of the most incredible sights I saw on the Great Barrier Reef was a group of six juvenile Valentine’s Pufferfish. These fish were about three centimetres long. The group was sauntering about the reef. Pufferfish have a silly little dorsal fin that is about one quarter as long as that of the Mimic Leatherjacket. The Leatherjacket is a perfect

The Titan Triggerfish short rear dorsal fin, the terminal mouth and the eyes high up on the head similar to Leatherjackets

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DIVE LOG Australasia #404 - February ‘23

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