Spotted Unicornfish (Naso brevirostris) Breeding Guide

Why Naso brevirostris is not bred at home: this large unicornfish forms pelagic spawning aggregations and produces long-lived acronurus larvae that drift in open water for up to 90 days.

Overview

The spotted unicornfish, Naso brevirostris, is a large surgeonfish of the family Acanthuridae ranging across the Indian and Pacific Oceans, from the Red Sea to the Hawaiian Islands and the Galápagos, on lagoon and seaward reefs down to about 46 m. It reaches around 60 cm and matures at roughly 25 cm in length. As a free-spawning reef fish it releases pelagic eggs into open water, which is why it is not reproduced in home aquaria.

Sexing

Males can be distinguished by larger keels on the caudal peduncle than females. There is otherwise no reliable external sexing method useful for a controlled pairing in captivity, and adults are too large to manipulate in home-aquarium conditions.

Spawning Behavior & Trigger

Naso brevirostris forms spawning aggregations and pairs to spawn, releasing eggs and sperm into the water column for external fertilisation. These open-water aggregations, driven by natural reef and lunar cycles, cannot be reproduced inside an aquarium.

Egg & Fry Care

Fertilised eggs are pelagic and develop into the transparent open-ocean larva typical of surgeonfishes, the acronurus, which can remain in the water column for up to about 90 days before settling on the reef. This prolonged planktonic phase, with its need for specialised micro-prey, is the central obstacle to rearing the species without dedicated hatchery technology.

Common Challenges

Captive reproduction of unicornfishes is not a documented home achievement. The combination of a pelagic spawning mode, an extremely long larval drift period and the adult's very large size confines any breeding attempt to research-scale marine aquaculture rather than the home aquarium.