What is a unicorn fish?
Unicornfish are marine fish in the genus Naso, part of the surgeonfish and tang family (Acanthuridae). The name comes from the horn-like projection on the forehead seen in some species, though others have no horn at all. They live on Indo-Pacific reefs, can grow large, and are fast, constant swimmers. Species sold to aquarists include the orangespine unicornfish (Naso lituratus), the bluespine unicornfish (Naso unicornis), and other species that vary greatly in size and feeding style.
Because the genus is diverse, “the” unicorn fish diet depends on the species. Check which one you are considering.
What unicorn fish eat in the wild
- Algae and seaweed. Several unicornfish are herbivores that graze on algae growing on reef surfaces, including brown algae such as Sargassum. The bluespine unicornfish is often cited as a mostly algae-eating species.
- Zooplankton. Other unicornfish, such as some of the larger or open-water species, feed mainly on plankton drifting in the water column.
- Mixed diets. Some species eat both algae and small animals, depending on age and location.
Marine biologists often group them as herbivores, planktivores or omnivores based on species, so it is wise to read species-level information before assuming a diet.
What to feed unicorn fish in an aquarium
For the algae-eating types that are most often kept at home, a herbivore-focused diet works best:
- Dried seaweed (nori). Offered on a clip, it is a common staple. Green, red and brown varieties add variety.
- Spirulina and herbivore formulas. Flakes, pellets and frozen preparations designed for tangs help cover nutrition.
- Live rock grazing. A mature tank with algae growth gives the fish natural grazing, though it will rarely cover the whole diet.
- Fresh macroalgae. Some keepers grow or buy macroalgae like Gracilaria as a supplement.
- Occasional meaty foods. Small amounts of mysis or brine shrimp are sometimes suggested for variety and condition, especially for omnivorous or plankton-eating species.
Avoid relying only on flake food. Plankton-feeding species may do better with frequent small feedings of frozen or live foods.
Feeding frequency and tips
- Feed often. Tangs and their relatives graze almost constantly. Many keepers offer several small meals per day, plus algae available all day.
- Introduce food gradually. New arrivals may be stressed and slow to eat. Offering nori, even if it is initially ignored, helps them recognize it as food.
- Watch body condition. A pinched belly or sunken head suggests underfeeding.
- Mind competition. Pushy tank mates can limit access to food at feeding time.
- Support the gut and immune system. Vitamin-enriched foods and good water quality are often recommended, since tang relatives can be prone to parasitic disease when stressed.
Are unicorn tangs hard to keep?
Unicornfish are not usually considered beginner fish. The main challenge is size and swimming space rather than a delicate diet. Many species reach a foot or more in length, and they need large tanks with long, open swimming lanes. They can also be territorial toward similar-looking fish and prone to stress-related problems when housed in cramped quarters.
If you are drawn to the group but have a smaller tank, consider smaller tangs after careful research rather than a Naso species. For more suggestions of eye-catching fish with realistic tank needs, see our list of cool saltwater fish to own.
Is unicorn fish safe to eat?
Unicornfish are eaten in some regions, but this is a food safety question with real risks. Certain tropical reef fish can carry ciguatera toxin, which can cause illness in people. Whether a given species or location is safe depends on local conditions, so follow local health and fisheries advisories. Fish sold for aquariums are not meant for consumption.
What fish is similar to a unicorn fish?
The closest relatives are other members of the surgeonfish and tang family, such as yellow tangs, blue tangs and sailfin tangs. These are also grazers that need algae-rich diets and good swimming space, and they often are better suited to home aquariums than the larger Naso species. Rabbitfish (family Siganidae) are another group of algae-eating reef fish that sometimes get compared to tangs. For more grazers, see our guide to the best algae-eating saltwater fish.
Related reading
If you are comparing display fish by cost and difficulty, you may also be interested in our look at the most expensive saltwater fish for aquariums.