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Meet "Lucy". Lucy is a seven-year-old queen triggerfish that was caught six years ago by a friend, and now lives at my education center. Triggerfish are found throughout the world in tropical and semi-tropical seas. Although extremely rare in New England, occasionally a young fry is carried by the Gulf Stream current up the coast from the Caribbean.

Triggerfish get their name from the unusual dorsal fins. The first spine on the dorsal is very thick and powerful, and together with the second spine on this fin form a locking mechanism to keep the spine erect. Triggers do this as a form of protection. When threatened they will squeeze their laterally compressed body into rock or coral crevices, erect the dorsal spine and lock it in place. This makes it nearly impossible for a predator to remove it from its hiding place.

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You can see in the photo above the large first dorsal spine. That smaller second spine behind it will tilt forward, locking the first spine in place. Once engaged, the spine cannot be moved unless the second spine is relaxed. The scientific name for this group of fish, Balistidae, originates from the Latin word for an ancient greek catapult. Ballistas were invented by Dionysus of Syracuse, but were not heavily used until the Punic Wars when Alexander the Great employed them as a siege weapon while storming fortresses. The dorsal fin of the triggerfish works like the ratcheted trigger mechanism of the catapult.

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Triggerfish swim using not their tails but by undulating the dorsal and ventral fins. This is known as sculling, and is helpful in the shallows to maneuver among rocks and coral heads as it searches for food. Although the mouth is small, it is very powerful and armed with large incisors that can crush nearly any shelled animal. The favorite food is crabs, but these fish aren’t picky. They are one of the few fish able to eat sea urchins and have evolved an ingenious way of attacking these sharp-spined animals. An urchin is protected by the spines on its entire body except for the mouth, which is facing down against the sand. Triggers will approach the urchin and blow a stream of water beneath the prey, tipping it over. The fish then grabs the unprotected mouthparts and, shaking its head, rips the urchin to shreds.

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Triggers are sand nesters. The males dig a shallow depression and the female deposits her eggs into it. Both parents tend to the nest and patrol it from predators around the clock. Any animal that comes close to it will be chased off, picked up and carried away or outright killed. Even a person who ventures too close will be attacked.

Hopefully Lucy will be with us for many years, as this species can live to an age of twenty. Although she has become very tame, readily taking food from our hands, she won’t tolerate any other animal in her tank.

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(Not "Lucy".)

Other diaries in this series can be found here.

Originally posted to Mark H on Fri Oct 19, 2007 at 04:48 PM PDT.

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