One Spot Foxface (Siganus Unimaculatus) saltwater aquarium fish

Overview:

The One Spot Foxface (Siganus unimaculatus) is a hardy marine rabbitfish valued for its algae-grazing habits and bold appearance. Despite its common name, it is not an invertebrate; it is a reef-associated fish that does best in a spacious, mature saltwater aquarium. Provide a tank of at least 75–100 gallons for a single specimen, with more room preferred as it grows to around 7–9 inches. Ideal conditions include stable reef-quality water, strong filtration, high oxygenation, and plenty of rockwork for grazing and shelter. Maintain temperatures around 72–78°F, salinity 1.023–1.026, pH 8.1–8.4, and low nitrate and phosphate. Good flow and open swimming space should be balanced with hiding places to reduce stress. Because it can produce a venomous dorsal spine defense, care should be taken during aquascaping and maintenance.

Diet and Feeding:

One Spot Foxface is primarily herbivorous, with a strong preference for marine algae and plant matter. Offer a varied diet built around nori, dried seaweed sheets, spirulina-based foods, algae wafers, and herbivore pellets. Supplement with blanched vegetables such as zucchini or spinach in moderation. It will also accept frozen meaty foods, but these should be occasional rather than the main diet, since too much protein can lead to digestive issues. Feed small portions 2–3 times daily, especially in younger or newly introduced fish, to encourage steady grazing and reduce aggression or stress. A healthy foxface should be active, constantly picking at rockwork, which helps control nuisance algae and supports overall well-being.

Compatibility:

The One Spot Foxface is generally peaceful and can be an excellent community fish, but it should be housed carefully. It is best suited to tankmates that are non-aggressive and not overly territorial. Compatible companions include tangs, clownfish, wrasses, gobies, cardinalfish, and many other moderately peaceful reef fish. Avoid housing it with highly aggressive species such as large dottybacks, triggers, and overly dominant angelfish that may harass it. It can coexist with corals in many reef systems, but individual behavior varies, and hungry specimens may nip at some soft corals or LPS if underfed. Keep only one foxface per tank unless the system is very large, as conspecific aggression can occur. It is usually not a threat to invertebrates like shrimp, snails, or crabs, but strong, active tankmates are preferred.

Health and Quarantine:

Quarantine is strongly recommended for 2–4 weeks before introducing a One Spot Foxface to the display tank. Observe for marine ich, velvet, flukes, fin erosion, poor appetite, or rapid breathing. These fish are sensitive to sudden changes in salinity, temperature, and pH, so acclimate slowly. Maintain excellent water quality and avoid overcrowding, as stress is a major trigger for illness. Provide ample algae and fiber-rich foods to prevent weight loss and digestive problems. When handling, never use bare hands near the dorsal spines, since they can deliver a painful venomous sting. Regular observation, stable parameters, and a varied diet are the best preventive care measures.

algae/nori spirulina mysis brine shrimp
The One Spot Foxface is an active, midwater-to-lower-level swimmer that needs plenty of open space as well as secure hiding spots and overhangs to retreat into when startled. It is generally peaceful to semi-aggressive, but can become territorial, especially toward conspecifics, so it is usually best kept singly unless in a very large system. A minimum tank size of 75 gallons is recommended, with ample rockwork and visual barriers to break up sightlines and reduce stress, while still preserving open swimming lanes. In reef setups, it is typically considered reef-safe with corals and most invertebrates, though its behavior should be monitored around very small tank mates and other similarly shaped herbivores. This species is primarily herbivorous, grazing continuously on filamentous algae, macroalgae, and supplemental vegetable foods such as nori and algae-based preparations. Occasional meaty foods may be accepted, but its long-term health depends on a diet centered on plant material and regular grazing opportunities.

FAQ

Frequently Asked Questions

About the One Spot Foxface

  • Why does my One Spot Foxface (Siganus unimaculatus) “glow” yellow one day and turn mottled brown/gray the next?
    This species has rapid color-shifting camouflage. Bright yellow usually means it feels secure, active, and relaxed; mottled brown/gray indicates stress, sleep, or trying to blend into rockwork. Sudden paling can also happen during nighttime, when startled by tank mates, or if water quality is poor. If the fish is still eating and breathing normally, the color change is usually normal.
  • Is a One Spot Foxface safe with zoanthids, soft corals, and LPS in a reef tank?
    It is generally considered one of the more reef-safe rabbitfish, but not fully guaranteed. Many individuals leave corals alone, especially in well-fed tanks, but some will nip zoanthids, fleshy LPS, and occasionally soft corals if hungry or underfed. They are much more likely to eat nuisance algae and macroalgae than coral, but each fish has its own personality. Feed heavily with algae-based foods to reduce risk.
  • How much algae does a One Spot Foxface actually need, and can it live in a tank that doesn’t grow much algae?
    It does not need a tank packed with natural algae to survive, but it does need frequent plant-based feeding. In captivity, it should be offered nori, spirulina-based pellets, herbivore flakes, and frozen herbivore blends daily. Natural algae grazing is a bonus, not a requirement. A sparsely algaed tank is fine if the diet is strong and varied; an underfed foxface may become stressed, skinny, or more likely to nip corals.
  • What tank size and aquascape work best for a One Spot Foxface, especially as it gets large?
    A juvenile may seem fine in a smaller tank, but adults get substantial and are active swimmers. A tank of at least 70–90 gallons is the practical minimum, with larger being better. They need long open swimming space plus lots of rockwork with caves and overhangs for security. Keep a tight-fitting lid or mesh cover, because startled foxfaces can jump. Also provide strong but not chaotic flow and plenty of grazing surfaces.
  • My One Spot Foxface keeps “playing dead” or lying on its side at night—should I worry?
    Usually no. One Spot Foxfaces often wedge into rockwork or rest on their sides at night, sometimes with their body color darkened, which can look alarming. They may also “freeze” and change color when frightened, making them seem lifeless. Worry only if the fish stays on its side during the day, stops eating, breathes rapidly, or becomes unresponsive for long periods. Those signs point to illness, poor acclimation, or water-quality problems.