Dr. Dwayne Meadows, NOAA/NMFS/OPR · Public domain — Wikimedia Commons
Saltwater Fish
Foxface Rabbitfish
Siganus vulpinus
Venom-spined algae mower with a fox's faceIntermediate
- Lifespan
- 8-12 years
- Size
- 24cm (9.5in)
- Social needs
- One per tank; peaceful with dissimilar fish
- Time
- Daily feeding; weekly testing and water changes
- Cost
- High
- Diet
- Herbivore-leaning omnivore (algae, nori, veg)
Overview
What is this animal?
- The Foxface Rabbitfish is a bright yellow grazer with a pointed, fox-like snout and a bold black-and-white banded face.
- It reaches around 24cm (9.5in) as an adult, so it is a genuinely large fish that outgrows midsize tanks.
- Its defining trait is defensive: the 13 dorsal spines, plus the anal and pelvic spines, are venomous, and a sting is sharply painful, so this is a fish you plan handling around.
- Compared with the tangs it is often bought alongside, the Foxface is hardier, thicker-skinned, and far less territorial, which makes it one of the more forgiving large marine herbivores.
- It is still not a beginner fish: the tank-size requirement is real, and nearly all stock is wild-caught from the Western Pacific because captive breeding is not yet commercially established.
- One quirk catches new keepers out: at night or when stressed it switches to a blotchy brown camouflage pattern.
- That mottling is normal and reversible, not a disease.
Temperament
- The Foxface is calm and peaceful toward almost everything it does not resemble, and because it is not a tang it usually coexists with a Yellow Tang or other surgeonfish without the turf wars tangs wage on each other.
- It spends the day openly grazing and cruising, raising its venomous dorsal fin and flashing mottled colour only when it feels threatened.
- Keep one per tank as the standard rule, since two Foxfaces will squabble unless they arrive as a bonded pair in a very large system.
- It ignores shrimp and small fish, so it fits over communities of gobies, blennies, and cardinalfish without risk.
- Its defence is entirely passive: it never attacks tankmates with its spines, but slow-moving fish that blunder into a raised fin can be stung, and so can a keeper's careless hand during aquascaping.
A good fit for
- Keepers with an established 120-gallon-plus system
- Reef tanks fighting hair or bubble algae
- Communities that already include a tang
- Intermediate marine keepers stepping up in size
- Aquarists wanting a hardier alternative to tangs
Common mistakes to avoid
- Venomous dorsal spines - never hand-catch or net carelessly
- Tanks under 120 gallons / 5ft cramp an adult
- Underfed individuals nip zoanthids and LPS corals
- Panicking over normal brown night-time mottling
- Nearly all stock is wild-caught - choose suppliers carefully
Enclosure
Minimum 450 litres (119 US gallons)
Must be housed alone. One per tank; peaceful with dissimilar fish
- Provide at least 450L (120 gal) with a tank length of 150cm (5ft) or more, because this is an active, open-water grazer that cruises the full run of the aquarium; a 6ft tank suits an adult better long term.
- Keep temperature 24-27°C (75-80°F), salinity 1.024-1.026, pH 8.1-8.4, and nitrate low with strong flow and good oxygenation.
- Aquascape with generous rockwork for grazing and a cave it can retreat to, while leaving clear swimming lanes along the front.
- A tight-fitting lid matters, since a startled Foxface can jump.
- Add it to an established tank with some natural algae growth rather than a newly cycled system, and quarantine it like any new marine fish.
- Plan the maintenance routine so you never need to grab it by hand: use a container to guide it rather than a net pressed against venomous spines.
Supplies
Setup
- Tank, stand and sump
- Return pump and powerheads
- Protein skimmer
- Reef lighting
- Rock and sand
- Salt mix, refractometer and test kits
- Quarantine tank
Ongoing
- Dried marine algae (nori) sheets in bulk
- Magnetic or suction veg clip
- Quality herbivore pellets
- Herbivore frozen food blend
- Second veg clip for a separate grazing station
- Vitamin or HUFA soaking supplement
- Small thawing cup
Safe substrate: Aragonite sand · Dry or cured live rock · Bare bottom
Care routine
Daily
- Check salinity, temperature and flow
- Clip on dried algae
- Feed
- Head-count and look everyone over
- Top up evaporation with fresh water
Weekly
- Service the skimmer and filter socksevery 3 days
- Clean the glass
- Plan hand work around the spines
- Test the water
Monthly
- Water changeevery 2 weeks
- Calibrate the refractometer
- Check salt, RO/DI and reagents
Less often
- Deep-clean pumps and powerheadsevery 3 months
- Replace RO/DI filter mediaevery 6 months
Vet: Quarterly herbivore review — every 3 months
Top resources for more info
Independent creators and organisations we would send a friend to. We have no affiliation with any of them, and nothing here is sponsored. Links checked 2026-09-19.
YouTubers
HumbleFish & ReefSaltwater fish disease, quarantine and treatment (Humble.Fish forum)BRStvReef tank setup, fish health and quarantine series (run by a retailer)FishOfHex AquaticsBeginner saltwater guides, avoiding common mistakes and tank disasters
Sites
Go deeper
Diet
- The Foxface is a herbivore-leaning omnivore whose diet must stay green.
- Offer dried marine algae (nori) on a clip daily, alongside quality herbivore pellets and occasional herbivore frozen foods.
- It grazes constantly and famously mows down hair algae, and many individuals will even pick at bubble algae that other fish ignore.
- Underfeeding is the classic mistake with this species.
- A hungry Foxface is the one that starts nipping zoanthids and fleshy LPS corals, which is why it is rated reef-safe only with caution.
- Keep it well fed with several small algae-based feedings and it generally leaves corals alone.
- A meaty, protein-heavy diet is the other error: it dulls colour and undermines long-term health, exactly as it does in tangs.
Health
- The Foxface has a thick slime coat and is noticeably more resistant to marine ich than the tangs on this site, but resistant is not immune, so quarantine every new arrival.
- Watch newly imported fish for a pinched belly, which signals starvation in the supply chain and calls for immediate, frequent algae feedings.
- As with other marine herbivores, chronic poor diet and water quality can lead to head-and-lateral-line erosion, so keep nitrate low and the diet algae-rich.
- Persistent dark mottling during the day, combined with hiding and refusal to eat, is the signal that something is actually wrong, as opposed to the normal night-time colour change.
- Keeper safety is part of the health picture here.
- A sting from the dorsal spines causes intense pain and swelling; immerse the wound in hot (not scalding) water and seek medical advice if symptoms spread or you have any allergic reaction.
Is your enclosure big enough?
Minimum volume450 litres (119 US gallons)
Swimming length150 cm minimum. A tall tank of the right volume is still the wrong shape.
CompanyMust be housed alone. One per tank; peaceful with dissimilar fish
Is this urgent?
In a reef, stability matters more than any single target number. A parameter moving fast does more damage than a parameter sitting slightly off.
Go now
Any detectable ammonia or nitriteWater change now with matched, mixed and aerated saltwater. Stop feeding. Directly toxic, and a marine system has less margin than a freshwater one.
NowTemperature or salinity has moved sharplyCorrect slowly, over hours, not minutes. Check the heater and the top-off. The speed of the change does the damage. Correcting fast repeats the injury in the other direction.
NowRapid gilling, or a fish hanging in the flow breathing hardIncrease aeration and check temperature and salinity. Warm water holds less oxygen, and a heater failure shows up here first.
NowToday
White spots, or a fine dusting like icing sugarIdentify which parasite before treating. Most reef tanks cannot be treated in place. The two common parasites look similar and need different handling; velvet can kill a tank in days.
TodayCorals closed for more than a day, or receding tissueTest alkalinity first, and compare it against the last reading rather than a target. Unstable alkalinity is the most commonly cited coral killer, and a swing shows up in the trend, never in a single point.
TodayA new fish added without quarantine now looks unwellRemove it to a separate system today if you can. Nearly every wipeout in a reef tank traces back to a skipped quarantine.
TodayQuarantine every new animal, including corals and inverts. It is the single practice that separates a reef that lasts from a reef that restarts.
This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it — and the time to find one is before you need one.
What it really costs
Setup, monthly, first year and across a whole life, itemised and with the electricity worked out from the actual wattage. Published figures for the same animal disagree by a factor of four, so the calculator shows ranges rather than picking one.
Bedding and substrate
In a marine system the rock and the sand are life support, and how you start them decides the first six months.
Safe
Aragonite sandThe standard marine substrate. Buffers pH and hosts the biology.
safeDry or cured live rockDry rock avoids importing pests but takes longer to mature. Cured rock is faster and riskier.
safeBare bottomCommon in high-flow systems. Easier to keep clean, but it removes a large part of the biological buffer.
safeWith a caveat
Deep sand bedsPowerful nutrient processing when they work and a sulphide release when they are disturbed. Choose shallow or deep deliberately, not by accident.
with a caveatUncured live rockIt will cycle the tank for you, and it will also bring in whatever was living in it.
with a caveatNever
Silica play sandDoes not buffer, and it is commonly blamed for feeding diatom blooms in a new tank.
neverAny rock or decor of unknown originMetals and phosphate leach for months and are almost impossible to trace once the tank is running.
neverThis is our general list for saltwater fish. We have not built one specific to Rabbitfish yet.
My kit says 0.25 ppm. Is that dangerous?
A liquid kit measures total ammonia, but only the un-ionised fraction is really toxic, and that fraction is governed by pH and temperature — each whole pH unit multiplies it roughly tenfold. So the same reading can be nearly harmless in one tank and lethal in another; this works out which one you are in.
Compare with other animals
The same axes for every animal, side by side — the way the guides are written makes that a fair comparison rather than two articles.
Keep going
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