Titan Triggerfish

Almost all recorded aggression from this species is nest defence rather than predation or random hostility. A female titan triggerfish lays her eggs in a wide, shallow depression she excavates in sand or rubble on the reef, and she then actively guards not just the nest itself but a large, cone-shaped volume of water above and around it, widest near the surface and narrowing down toward the eggs. Anything that enters this zone, whether a fish, a turtle, or a human diver, may be charged, bumped, and bitten regardless of whether it poses any real threat to the nest, and divers who unknowingly swim over an active nest are the most common cause of encounters. Outside the breeding season, titan triggerfish are far less aggressive and mostly avoid people.

Strong enough to be taken seriously. The titan triggerfish has robust, fused, beak-like teeth adapted for crushing the hard shells of sea urchins, crabs, and molluscs and even biting into coral, and the same bite applied to a person can break the skin, cause deep bruising, tear wetsuit fabric and swim fin material, and in some documented cases has drawn enough blood to require stitches. It is not venomous and the bites are not life-threatening, but the combination of a large, fast, aggressive fish and a genuinely powerful bite makes it one of the few reef fish that dive guides specifically warn divers about, especially during the breeding season.

Triggerfish, including the titan triggerfish, have two spines at the front of the dorsal fin instead of the usual soft rays. The first, larger spine can be locked rigidly upright, and it can only be released and folded back down by first depressing the smaller second spine just behind it, in a mechanism similar to a gun's trigger and safety catch. In the wild this lets a triggerfish wedge itself firmly into a reef crevice or hole to sleep or to escape a predator; once the main spine is locked upright and the fish is braced inside a gap, it becomes very difficult to pull out, since pulling only jams the spine harder against the roof of the crevice.

Dive guides generally recommend not turning your back and swimming straight up, since the fish's defended territory is shaped like a cone that widens as it rises toward the surface, meaning a diver moving straight upward may stay inside the danger zone for longer and end up close to the surface with an agitated fish still nearby. Instead, the recommended response is to face the fish, keep an eye on it, and swim away horizontally, which exits the narrower base of the cone more quickly, and if necessary to place a camera, fin, or other object between yourself and the fish as it charges, since it will often bite the nearest available object rather than a hand or leg.