Heniochus monoceros (Mask Bannerfish / “Unicorn” Bannerfish) is a striking, open-water butterflyfish relative known for its bold black-and-white bands, yellow accents, and elegant trailing dorsal filament. It’s an active, display-focused species that brings constant movement and personality to larger marine aquariums, often spending its day cruising mid-water and interacting with its surroundings. With the right setup and a steady feeding routine, it can become a confident, showpiece fish that settles in well and feeds eagerly.
For best long-term success, house H. monoceros in a larger, mature aquarium with plenty of swimming room, stable parameters, and strong filtration. Provide a mix of open areas and rockwork for shelter, along with moderate to strong water movement and high oxygenation. Like many bannerfish, it appreciates stability—sudden swings in salinity, temperature, or water quality can lead to stress and reduced feeding response. Aim for consistent, reef-appropriate conditions and avoid overcrowding.
Diet is a key part of keeping this species thriving. Offer a varied meaty menu 2–3 times daily: quality frozen foods (mysis, brine, chopped prawn/seafood blends), plus marine pellets and flakes once acclimated. Variety helps maintain condition and colour, and frequent smaller feedings suit its active metabolism. A quarantine/acclimation period is strongly recommended, both to ensure it’s eating strongly and to reduce the risk of introducing parasites.
In terms of temperament, Heniochus monoceros is generally peaceful to semi-peaceful and does best with non-aggressive tankmates in a community-style marine setup. Avoid housing with highly territorial or bullying species that may outcompete it at feeding time. Many hobbyists have success keeping bannerfish in pairs or groups only in sufficiently large systems—otherwise, a single specimen is often the safest choice unless you’re confident in tank size and compatibility.
Reef compatibility is mixed. While some individuals behave well in reef aquariums, this species can nip at soft corals, LPS, and polyps, especially if underfed or if it develops a taste for certain corals. It’s usually best described as “reef with caution” and is often most reliable in a fish-only or mixed reef where coral selection is chosen carefully. If you’re aiming for a coral-heavy display, plan accordingly and monitor behaviour closely during the first few weeks.
