Overview
The Bluelined Surgeonfish (Acanthurus nigroris) is a vibrant, ecologically essential acanthurid fish widespread across the clear, surge-swept coral reefs of the central Pacific. Famous for its fine, electric-blue longitudinal pinstripes and distinctive caudal scalpels, this active grazer plays a keystone role in maintaining the delicate competitive balance between hermatypic corals and marine algae.
Biology and Physical Characteristics
Acanthurus nigroris features an oval, laterally compressed body cloaked in a dark chocolate-brown to rich olive-slate ground color, adorned with dozens of delicate, wavy, horizontal iridescent blue lines that shimmer in the sunlight. Like all surgeonfishes, it possesses a razor-sharp, forward-pointing modified spine (the scalpel) folded within a sheath on either side of the caudal peduncle, highlighted by a conspicuous dark oval spot. Its terminal mouth contains specialized spatulate teeth tailored for cropping filamentous turf algae without fracturing underlying coral skeletons.
Behavior and Ecology
Highly mobile and gregarious, the bluelined surgeonfish frequently forms dense mixed-species foraging schools alongside parrotfishes and tangs. Moving in coordinated waves across exposed reef crests and shallow reef flats, these schools overwhelm territorial damselfishes to graze intensely on nutrient-rich algal turfs. By clearing away turf algae, they prevent coral smothering and open clean bare substrate essential for the settlement of new coral planula larvae.
Conservation and Human Impact
Evaluated as Least Concern by the IUCN, Acanthurus nigroris is abundant throughout its central Pacific range. While harvested moderately by subsistence spearfishers and collected occasionally for the marine aquarium trade, populations remain robust in well-managed marine protected areas. Long-term threats stem primarily from coral bleaching events and ocean warming that reduce structural reef rugosity.
Interesting Factoid
The razor-sharp ‘scalpels’ on either side of this surgeonfish’s tail hinge outward like switchblades when the fish flexes its tail, providing a lethal weapon that can slice deep wounds into attacking predators!
Last updated: October 2026