Acanthurus gahhm is one of the 38 members of the genus Acanthurus, which together with 5 additional genera make up the surgeonfishes family (Acanthuridae) in which a total of 73 species are currently described. This species inhabits the inner bottoms of bays and lagoons with sandy bottoms, as well as at the base of outer reefs. We will always find them in waters less than 40 meters deep, and their distribution range includes the Indian Ocean.
The body of Acanthurus gahhm is typical of a surgeonfish, that is to say laterally compressed and oval. It can reach up to 40 cm in length. It has a small mouth, which is protractile and is placed slightly on the lower part of the snout. The dorsal fin is continuous and has 9 spines and 24-28 soft rays, the anal fin has 3 spines and 23-26 soft rays, and the caudal fin is lunate in shape. Characteristic of this family of fish, on the caudal peduncle we find a retractable spine on each side, which it will use as a defensive method if it feels attacked.
Acanthurus gahhm is characterized by two small lateral dark bands, one from the posterior margin of the eye towards the tail, and the other from the spine of the caudal peduncle towards the head. These two bands do not appear until the individual reaches 5 cm in length, in the first one, and until it reaches 10 cm for the second line. Their base coloration varies from blue-grayish, sometimes almost black, to brownish-grayish. The fins are the same color as the body, and the dorsal fin has the outer margin edged in yellow. The caudal fin has a white stripe at its base. The outer third of the pectoral fin is greenish yellow.
Acanthurus gahhm is an omnivorous species, feeding on organic detritus, small benthic invertebrates and algae.
They have no apparent sexual dimorphism. They reproduce oviparously with external fertilization and form stable breeding pairs. The female will spawn in the water column, and the male will then release the sperm so that the eggs are fertilized and dispersed by the currents. After 24 hours, the larvae will hatch. The larvae have a translucent back half of the body and a silvery front half and are known as Acronurus. The larval head is triangular in shape, with large eyes and large pectoral fins. The larva will undergo metamorphosis to become an adult specimen.
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