Fish That Will Eat Your Corals (and the Ones That Actually Are Reef Safe)

“Reef safe” is the most misleading phrase in this hobby, and it is printed on tanks full of fish that will eat your corals. It is not a lie exactly. It is just far too blunt an instrument. A snowflake eel is sold as reef safe with caution and is completely harmless to every coral you own — and will eat every shrimp and crab in the tank. A flame angel is sold the same way and is the exact reverse. The label tells you there is a risk. It does not tell you what the risk is to, which is the only part that matters. So the useful question is not “is this fish reef safe?” It is: what specifically is this fish not safe with, and do I own that? This article answers that. It is the companion piece to Reef Safe Fish for Beginners — that one is about what to buy, this one is about what will cost you a colony.

The absolute no list

These are not judgment calls. These fish eat coral as a matter of biology, and no amount of feeding changes it.

Large angelfish

Pomacanthus, Holacanthus, Apolemichthys — emperors, French, queen, majestic, rock beauty, flagfin. In the wild they eat sponges and tunicates. In your tank there are no sponges, so they redirect onto coral tissue, and the targets are consistent: fleshy LPS above all. Open brains, Symphyllia, Lobophyllia, scolys, cynarinas. Clam mantles. Zoanthids. The trap is that juveniles are often fine. A young emperor can behave perfectly for two or three years and then flip, and once a fish has learned what a Trachyphyllia tastes like it does not unlearn it. “He’s been fine for two years” is not evidence of anything. The genuine exception is Genicanthus — the swallowtail and lyretail angels. They are zooplankton feeders with small mouths built for picking food out of the water column, and they are the one angelfish genus that belongs in a coral tank. They need space, 120 gallons and up.

Butterflyfish — where the genus decides everything

Some butterflyfish are obligate corallivores. They eat stony coral polyps and essentially nothing else, which means they will strip your reef and then starve when it runs out. The chevron (Chaetodon trifascialis) feeds almost exclusively on Acropora hyacinthus in the wild. Meyer’s, ornate and reticulated butterflies rely on SPS polyps almost entirely. These are beautiful fish that cannot be kept in a reef tank and, honestly, are difficult to keep at all. The common ones sold in stores — raccoon, threadfin, double-saddle, Klein’s — are generalists. Less specialized, still a bad bet with coral. The ones that are genuinely reef safe are worth knowing because most people assume no butterflyfish is:

• Pyramid butterflies (Hemitaurichthys polylepis, H. zoster) — obligate plankton feeders, and the safest butterflyfish genus for a mixed reef by a wide margin. They can even be kept in small groups in a big tank.
• Schooling bannerfish (Heniochus diphreutes) — a zooplankton feeder and reliably reef safe. Careful: it is constantly confused in stores with the longfin bannerfish (H. acuminatus), which is a bottom feeder and is not a safe bet. The schooling one has a shorter snout and a deeper body.
• Longnose butterflies (Forcipiger) — that forceps mouth physically cannot work a coral polyp. They pick small crustaceans from crevices. They will eat your feather dusters.

Triggers, puffers, parrotfish and filefish

Most triggerfish — Picasso, huma huma, clown, undulated, queen — hunt benthic invertebrates and rearrange rockwork doing it. They will flip frags, crush snails and eat clams. The planktivorous exceptions, blue-throat and crosshatch, are much better reef citizens and are legitimately kept in reefs, but even they will eventually take a small shrimp. Large puffers have beaks built to crush shelled prey, and that beak needs hard food to keep it filed down. Snails, hermits, crabs, clams, urchins — all of it. They nip coral and live rock too. FOWLR only. The small tobies (Canthigaster — Valentini, blue-spot) get marketed as reef safe with caution and are the definition of a coin flip. They will reliably eat shrimp and snails. Coral nipping is individual: plenty of keepers report years with no coral damage, plenty report one that suddenly developed a taste for zoas. They also nip other fish’s fins. One veteran’s summary is about right — roughly 50/50 at playing well with others, and not worth it around corals you love. Parrotfish bite coral and skeleton. Blanket no, and most species get far too large regardless. Filefish deserve a specific warning. The harlequin filefish (Oxymonacanthus longirostris) is a textbook obligate Acropora eater. And the “aiptasia-eating” filefish (Acreichthys tomentosus) has a well-earned reputation: ORA’s own product page says they are not always reef safe and recommends keeping them in a refugium rather than the display. The pattern in hobbyist reports is remarkably consistent — it clears the aiptasia, then it moves on to your zoas, acans and torches. If you use one, plan to remove it the moment the aiptasia is gone, and own a trap before you buy the fish.

Wrasses that are simply not reef safe

Coris (yellowtail, African), Thalassoma (lunare, bluehead) and Gomphosus (bird wrasse) are large, fast invertebrate hunters. They will strip a clean-up crew and topple frags digging in the sand. They are sold small and cute and reach twelve to fifteen inches. A naming note that trips people up constantly: the yellow “coris” wrasse (Halichoeres chrysus) is not a Coris at all. It is a different, far more reef-appropriate fish. Do not let the common name talk you out of a good wrasse or into a bad one.

The risky maybes — where it genuinely is a coin flip

Dwarf angels

This is the argument everyone has, so here is the honest version. There is no reliable failure rate. Nobody has run a survey with a real denominator, and anyone quoting you a percentage is making it up. What the collective experience does support is this: the behavior is individual rather than species-determined. As one long-time reefer put it, twenty-three people can tell you theirs was a model citizen and yours still won’t be. What matters more than which dwarf angel is which corals you keep. Fleshy LPS — acans, blastos, scolys, open brains, chalices — and clam mantles are the high-risk assets. Zoanthids are contested. SPS is comparatively low risk. If your tank is predominantly SPS, a flame angel is a reasonable gamble. If you keep acans you actually care about, the odds get considerably worse. Roughly, and with the caveat that sources disagree:

• Better odds: coral beauty is the most consistently well-reviewed. Flame angel has a worse reputation for LPS and zoas but plenty of multi-year clean records.
• Worth flagging: the common internet advice that the smallest species — cherub/argi, African flameback — are automatically the safest is not borne out by field reports. Both have documented cases of wiping out zoa colonies and damaging scolys.
• Worst for a coral tank: lemonpeel and bicolor, named consistently across every source. Also half-black, Herald’s, and midnight.

Feeding heavily helps with herbivores. With angels the evidence is split — some keepers who feed three times a day report far fewer problems, and Reef Builders argues flatly that there is no trick and it is simply instinct. Both positions have evidence behind them. What does reliably help: add the angel last, to a mature tank already full of coral and grazable algae. Give it a big tank. And own a fish trap before you buy it — netting a dwarf angel out of a coral-packed rockscape is how people end up draining a display.

Copperband butterfly

The reef risk is real but modest — feather dusters and tubeworms reliably, clam mantles frequently, the occasional LPS nip, and some individuals do develop a taste for zoas. The bigger problem is that most of them die. They very often refuse prepared food and fade away over weeks or months. Buy one you have personally watched eat in the store, or do not buy one. And do not buy one as an aiptasia solution — some eat it, plenty do not.

Tangs and rabbitfish

Both are herbivores with no coral-crushing dentition, and both are structurally safe. When they do nip coral, it is almost always a nutrition problem — one well-documented case of a tang picking at Goniopora started right after the owner stopped putting nori on a clip. Keep seaweed available constantly and most of this disappears. Foxface rabbitfish appear on both the “best” and “worst” reef-safe-with-caution lists in the same discussion thread, which is the perfect illustration of individual variation. When they go bad they go for zoas, fleshy LPS, Xenia and leathers. On tank size, since we would rather be honest than sell you a fish: think in terms of tank length rather than gallons. Bristletooths like Kole and Tomini want four feet. Yellow, purple and scopas want five. Powder blues, powder browns and Achilles want six-plus — and powder blues are notorious ich magnets on top of it. Hippos and Nasos need more tank than most people reading this have.

Blennies — the under-reported one

Most people file blennies under “safe.” That is mostly right and not entirely. Ecsenius blennies — bicolor, tricolor, tailspot, lineatus — have well-documented reports of nipping SPS, particularly Montipora and Acropora, leaving small white patches where polyps were. Bicolor blennies picking at clam mantles is a recurring complaint. The Midas blenny (Ecsenius midas) is largely planktivorous and is the one generally trusted. As an experienced keeper put it: other than Midas, treat all blennies as potential polyp eaters. Most don’t. Some do.

Clownfish and your Euphyllia

Clownfish do not eat coral. The damage is mechanical — a clown that decides your hammer is an anemone will thrash around in it, abrading tissue and preventing the polyps from expanding. Most of the time this is fine and the coral adapts. It goes wrong when a large clown adopts a small or delicate colony. Big colonies tolerate it; a single-head frag does not. Wall hammers are more sensitive than branching hammers, and one clown is gentler than a pair. Watch specifically for a clown biting at the bubbles rather than just nestling. If you want it stopped, physically block access or move the coral. Discouraging the fish does not work.

Safe for your coral, lethal for your clean-up crew

This distinction costs beginners real money, because a cleaner shrimp is not a cheap animal and “reef safe” does not cover it. Hawkfish are the number one shrimp killer sold as reef safe. Flame, longnose, falco, arc-eye — all of them are ambush predators with a taste for crustaceans, and feeding them well does not suppress the instinct. Sexy shrimp are almost always taken. Cleaner shrimp are at real risk. They also perch constantly, and repeated perching on delicate branching SPS abrades the tissue at the perch site, which people routinely misread as disease. Halichoeres wrasses — melanurus, yellow coris and their relatives — are low risk to coral and a genuine risk to inverts. They will grab a small snail and bang it against the rock until it comes out of the shell. Some individuals never hunt anything but pods; others clear a clean-up crew entirely. Lionfish are completely coral safe, which surprises people, and will eat any fish or shrimp that fits in that very large mouth. Same for groupers, frogfish and snowflake eels — harmless to your corals, and they will systematically eat every crustacean you own. If you are adding a predator, add the shrimp first and let them establish and grow. A large Lysmata cleaner survives far better than a sexy shrimp, and a pistol shrimp settled into a burrow is usually the one crustacean that makes it.

How to tell a fish did it

Before you accuse a fish, learn what fish damage actually looks like, because pests, chemistry and lighting all produce tissue loss too. Fish predation is directional and selective. The damage is concentrated on the face of the colony the fish can reach, and the sheltered side is untouched. One coral, or one type of coral, is hit while everything else in the same flow and light is perfectly happy. If your alkalinity swung, everything would be unhappy. If only the acan is missing tissue, that is a mouth. Look at the edges. Fish bites leave clean, scooped, scalloped margins, often with a bit of skeleton showing right at the bite. Blenny and angel nipping on SPS shows as discrete white patches where polyps were removed, with intact tissue around them. Brown jelly, RTN and alkalinity problems make tissue slide off in sheets or recede uniformly. Check the clock. Fish feed with the lights on. If the coral looks fine at night and chewed during the day, that is a fish. Pests are the opposite — flatworms, nudibranchs and predatory snails feed at night, so pest damage appears overnight and you find it in the morning.

Catching the culprit

1. Point a camera at it. A phone on a tripod or a cheap wifi cam recording an hour, scrubbed through at 8×, is the most reliable method available and the most underused. Fish do not graze while you are standing at the glass.
2. Watch quietly from a distance for twenty minutes, ideally around lights-on.
3. Check at night with a dim red light for the nocturnal suspects — hitchhiker crabs, nudibranchs, predatory snails, bristle stars.
4. Rule out pests first. Dip the coral in a white container and blast it with a baster. See our Coral Pests 101 guide for what falls out and what it means. Check the underside and the base — that is where the zoa and Montipora nudibranchs hide, camouflaged to match the coral they are eating.
5. Move the coral. Elevate it out of reach or put it in the sump for two weeks. If it recovers, you have your answer without catching anything.

The test to run before you buy any “with caution” fish

Three questions. If any answer is no, do not buy the fish.

1. Which of my corals would I be genuinely upset to lose? If the answer includes fleshy LPS or clams and you are considering a dwarf angel, you already have your answer.
2. Can I physically get this fish out of my rockwork? Do you own a trap? Netting through a coral-packed reef does more damage than the fish did.
3. Where would it go? A sump, a quarantine tank, store credit, another reefer. If there is no exit, you are committing permanently to a coin flip.

There is one more piece of advice, and it is the most useful thing in this article: stop trying to make the fish safe and pick corals it does not want. If you have your heart set on a dwarf angel, build an SPS-dominant tank and skip the zoa garden. That works far more reliably than any feeding regimen.

Where ours come from

Everything we grow is aquacultured in Key West, and we would rather sell you a coral that lives than a coral that becomes a fish’s lunch in two weeks. If you tell us what is already swimming in your tank, we will tell you honestly which of our pieces are a bad idea for it — including when the honest answer is that your fish list and your coral list do not go together.

Ask us first

If you are weighing up a fish and you are not sure, send us your stock list before you buy rather than after. We have watched a lot of people learn this the expensive way, and there is no reason for you to be one of them.

Working out what got eaten starts with knowing what it was. The Coral Field Guide covers 27 aquarium corals with the feature that identifies each one.