Alexandre Prévot · CC BY-SA 2.0 · Wikimedia Commons (cropped)

Saltwater Fish

Foxface Rabbitfish

Siganus vulpinus

Venom-spined algae mower with a fox's faceIntermediate

Lifespan: 8-12 years
Size: 9.5 in
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 9.5 in 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.

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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.

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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 265-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, anal and pelvic spines - never hand-catch or net carelessly
Tanks under 265 gal or 5 ft long
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 265 gallons

One of its kind per tank; other compatible species can share it. One per tank; peaceful with dissimilar fish

Provide at least 265 gal with a tank length of 5 ft or more, because this is an active, open-water grazer that cruises the full run of the aquarium; a 6 ft tank suits an adult better long term.
Care references give 125 gal for an adult.
This guide asks for more because good conditions are never less than a law requires, and Austria's law asks 265 gal for a rabbitfish this size.

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The 75 gal still quoted in some guides suits only a young fish.
Keep temperature 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.

Check your enclosure

Supplies

Setup

Tank, stand and sump
Return pump and powerheads
Protein skimmer
Reef lighting
Rock and sand

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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

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Vitamin or HUFA soaking supplement
Small thawing cup

Safe substrate: Aragonite sand · Dry or cured live rock

Work out the cost

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

Every few days

Service the skimmer and filter socksevery 3 days

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Weekly

Clean the glass
Plan hand work around the spines
Test the water
Water change

Monthly

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

Health review: Quarterly herbivore review, every 3 months

Tools

Is your enclosure big enough?Check your measurements against the recommended size What will it cost?Setup, monthly and over its whole life, itemised Is this ammonia reading dangerous?Works out the toxic part from your pH and temperature

Care in depth

Diet

Herbivore-leaning omnivore (algae, nori, veg)

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

Signs of good health, and the common problems

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 any of the fin 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 this urgent?

6 warning signs and how fast to act, 3 of them right away

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. Ammonia is directly toxic, and at reef pH more of it is in the toxic form, so a marine system has less margin than a freshwater one. Nitrite is far less toxic in seawater, but any reading in a stocked tank means the biological filter is not keeping up.

Now

Temperature 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.

Now

Rapid 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.

Now

Today

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.

Today

Corals 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.

Today

A 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.

Today

Quarantine 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.

Bedding and substrate

2 safe, 3 with a caveat, 2 to avoid

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, and it hosts the biology. It does not meaningfully hold pH or alkalinity at normal reef pH, so test and dose for those regardless.

safe

Dry or cured live rockDry rock avoids importing pests but takes longer to mature. Cured rock is faster and riskier.

safe

With 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. A sand-sifting or burrowing goby needs a fine bed about 2 to 3 in deep that it turns over itself. That is a different thing from a denitrifying deep sand bed (4 in or more, left undisturbed), and the two do not mix: a sifting goby disturbs the layers a deep sand bed depends on and eats the life in it.

with a caveat

Uncured live rockIt will cycle the tank for you, and it will also bring in whatever was living in it.

with a caveat

Bare bottomWorkable in high-flow systems for fish that neither sift nor burrow, but it removes a large part of the biological buffer. Wrong for watchman gobies and other gobies that burrow or sift, which need a fine sand bed at least 2 in deep to dig and feed in, and for mandarins and other copepod-eaters, which need sand as well as mature rock for their food to breed in.

with a caveat

Never

Silica play sandNot the marine standard, and commonly blamed for feeding diatom blooms in a new tank.

never

Any rock or decor of unknown originMetals and phosphate leach for months and are almost impossible to trace once the tank is running.

never

This is our general list for saltwater fish. We have not built one specific to Rabbitfish yet.

Top resources for more info

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