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How do triggerfishes lock their first dorsal spine in an upright position?
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tetraodontiform
Scrawled filefish (Aluterus scriptus)
Triggerfishes, which belong to the family Balistidae, possess a specialized mechanism involving their first two dorsal fin spines to lock themselves in place. When the fish erects its large, strong first dorsal spine, the second spine acts as a "trigger" that locks the first one in an upright position. This adaptation allows the fish to wedge itself tightly into protective reef crevices. To release the first spine, the second spine must be withdrawn.12