Coral Eating Fish: The Intriguing Relationship Between Corals and Fish

The relationship between corals and fish is complex and multifaceted. Coral reefs are home to over 4,000 fish species, providing them with food, shelter, and a place to breed. At the same time, fish play a vital role in helping maintain the health of coral reefs through grazing, cleaning, and fertilizing. This symbiotic relationship is critical to the survival of both corals and fish.

However, the coral-fish dynamic also has its dark side. Some species of fish directly feed on coral, eroding the reefs. There are also instances of corals turning the tables and consuming small fish! This article will explore the fascinating and sometimes disturbing connections between corals and fish. We’ll uncover whether corals eat fish, look at fish species that gnaw away at coral skeletons, and examine how the two very different organisms rely on each other.

Do Corals Eat Fish?

One of the most intriguing questions regarding the coral-fish relationship is whether corals actively hunt and eat fish. Internet forums contain anecdotal accounts of corals, especially large polyp stony (LPS) species like frogspawn and hammer corals, grabbing and ingesting small fish. But is there any scientific proof to back these claims? Or are corals just passive filter feeders surviving on plankton?

Some real-life incidents certainly seem to point to corals being able to catch fish. In one example, a reef aquarist returned home to find only the head of their emerald crab sitting on the sand bed. All claws and legs were missing. The culprit – a huge frogspawn coral with a mouth still wide open. The aquarist surmised the crab had gotten too close and been snatched by the voracious coral.

Another account describes a hammer coral ingesting a tail-nipping chromis. The fish had been irritating the coral by biting its flesh. The coral responded by opening up and swallowing the chromis whole! The fish was still visible inside the coral’s mouth days later.

These anecdotes demonstrate corals acting against annoying fish rather than actively hunting them. But there are also examples of corals consuming small fish without provocation. A video posted online by a marine park shows a large elegance coral catching and eating a tiny fish whole, stunning onlookers. The coral stretched out its flowing tentacles and grabbed the unsuspecting fish as it swam by.

The Frogspawn Incident

One heated debate on an aquarium forum centered around a frogspawn coral suspected of eating a clown goby fish. The aquarist had placed a new goby into the tank and it disappeared overnight. The usually wide open frogspawn was tightly sealed in the morning with tentacles retracted. The aquarist concluded that the big LPS coral had attacked and consumed the small fish.

Forum members weighed in, arguing whether a frogspawn could and would eat a two inch fish. One user vehemently denied it, stating frogspawns only eat plankton and microorganisms. However, others shared personal experiences of their corals eating surprising foods like sea slugs and urchin spikes. “My frogspawn is very aggressive and has eaten large meaty foods I’ve put in the tank,” one reefkeeper noted. “A goby wouldn’t be beyond its abilities.”

The controversy around the frogspawn incident highlights the limited scientific evidence around corals actively hunting fish. Anecdotes suggest it is possible under certain circumstances. But more research is needed to prove that corals can be cunning fish hunters. Tank observations indicate that corals usually respond to fish only if bothered or irritated. Catching a meal seems to be opportunistic rather than their prime feeding strategy.

The Other Side of the Coin – Fish That Eat Corals

While corals eating fish occurs rarely, the opposite situation is very common. Many species of fish directly feed on stony corals and act as bioeroders, gradually gnawing away the reef framework. The main culprits are triggerfish and parrotfish, two groups specialising in taking coral bites. While their coral munching habits help recycle nutrients, excessive feeding can destroy coral colonies and weaken reef structures.

Parrotfish (Scaridae family) are particularly coralivores that depend on corals for their sustenance. Their stout beaks continuously scrape and bite off pieces of coral and algae. A parrotfish crunches up chunks of reef skeletons with big powerful jaws, digests the nutritious matter, then excretes the powdered coral as sand.

Parrotfish produce a large amount of the white sands found in tropical environments. Each parrotfish can manufacture over 2,000 pounds of sand per year. Their grazing is essential for clearing away dead coral and opening up space for new coral growth. Parrotfish may eat away at reefs, but they also help build beaches!

The Parrotfish Phenomenon

With over 80 species, parrotfish are a highly diverse and ecologically important fish group. Their coral crunching behavior benefits reefs by removing algae, recycling nutrients, and producing clean new sands. A single parrotfish can grind up several tons of calcium carbonate each year, making these prolific bioeroders.

However, an excess of parrotfish grazing can overwhelm and degrade local coral ecosystems. When populations are balanced, parrotfish aid reef regeneration and maintenance. But overfishing of predators allows parrotfish numbers to boom, leading to coral depletion. This demonstrates the complex interdependence between parrotfish and corals on tropical reefs.

Triggerfish – The Coral Menace

While parrotfish nibble away gradually at coral structures, triggerfish are more overtly destructive. These pugnacious fish take sizable bites right out of coral heads. Their sturdy teeth and jaws allow them to carve out chunks of reef framework. Triggerfish also aggressively defend feeding territories, attacking divers and snorkelers who approach.

Of particular concern is the titan triggerfish (Balistoides viridescens) found throughout the Indo-Pacific. These bullish fish establishes feeding scars on coral heads which enlarges over time, leaving only the skeleton behind. Studies have tracked how triggerfish significantly reduce live coral cover by extending their bite scars.

Triggerfish are certainly one of the most damaging coral predators. As triggerfish populations rise, the health of coral reef ecosystems decline. Their territorial nature also makes them hazardous to people. Many divers in triggerfish areas report being bitten and chased by these temperamental coral munchers. There is still much to learn about curbing triggerfish destruction while conserving this important species.

The Waste Management System

Corals and fish coexist by utilizing each other’s metabolic waste products. Corals receive vital nutrients from fish excrement and other debris fertilising their endosymbiotic algae. In turn, fish benefit from corals filtering and processing waste material from the water column. This waste recycling contributes to the effective functioning of coral ecosystems.

On coral reefs, fish generate copious amounts of ammonia, nitrates and phosphates through their gills and excretory systems. These chemicals are toxic in high doses. But they serve as crucial plant fertilizers in lower concentrations. Endosymbiotic algae called zooxanthellae living within coral tissues can utilize these nutrients and encourage coral growth.

Meanwhile, corals act as natural water filters, trapping floating particles and absorbing dissolved elements like nitrates. This filtration creates a cleaner, healthier habitat for fish populations. The efficient nutrient exchange and waste recycling between corals and fish is an often overlooked aspect of their symbiotic relationship.

The Starfish Connection

Another coral predator closely tied to fish populations is the crown-of-thorns starfish. These coral-eating starfish can play an important ecological role by preying on fast-growing corals. However, without natural population controls, starfish numbers boom into outbreaks that devastate reefs.

A major factor in starfish outbreaks is the loss of predator fish through overfishing. Triggerfish and pufferfish are starfish predators that help keep their numbers regulated. Removing these natural predators allows crown-of-thorns populations to explode. A starfish can destroy up to 66 feet (20 meters) of healthy coral in one year.

A major outbreak can wipe out vast swathes of coral reefs. Controlling starfish outbreaks requires an ecosystem-wide approach, including managing key fish species that prey on them. Otherwise, these coral-devouring starfish can quickly consume living coral faster than reefs recover. The interconnections highlight how fish populations directly influence the prevalence of coral-eating starfish.

The Great Barrier Reef – A Case Study

The complex symbiotic dance between fish and coral plays out on a grand scale across the Great Barrier Reef along northeastern Australia. This 1,400 mile long reef system contains over 900 coral species and 1,500 fish species. The sheer diversity of hard and soft corals provides ample feeding and nesting habitat for myriad fish.

Bumper populations of parrofish, triggerfish, sweetlips and many other fish make this reef their home. Schools of fish swarm and feed amidst the corals while fertilizing and cleaning them.

However, a delicate balance is needed. Overfishing of key species like parrotfish can prevent the bioerosion needed to renew reef habitats. And declining predator fish causes crown-of-thorns starfish outbreaks that decimate coral colonies. Climate change leading to coral bleaching further weakens the ecosystem.

The health of the Great Barrier Reef demonstrates the close interdependence between coral structures and fish communities. Disrupting one side of this relationship can damage the entire marine ecosystem. While parrotfish and other coral predators play a role in reef dynamics, overactivity destroys the very habitat they rely on.

Likewise, protecting predator fish is crucial for controlling starfish outbreaks. The interconnectivity of life on the reef highlights the need for an integrated approach to conservation. The future of coral reefs like the Great Barrier depends on nurturing the complex symbiotic relationship between fish and coral species.

Additional Research and Observations:

The Frogspawn Incident

A discussion on Reef2Reef forum suggests that frogspawn corals can consume small fish like clown gobies. One user mentioned that their frogspawn coral was “very aggressive” and had eaten large meaty food and even sea slugs. This helps explain how a hungry frogspawn could have eaten the missing goby fish.

My Fish is Eating My Coral!

Unfortunately, fish nibbling on coral polyps is common in home aquariums, especially with territorial fish like damsels. Target feeding aggressive fish can help curb this behavior. Other options include removing the coral-munching fish or adding a predator to deter biting.

Elegance Coral Eating Fish – The viral video shows a large, elegant coral (Catalaphyllia jardinei) grabbing and eating a tiny fish. This demonstrates that large LPS corals can catch small passing fish, likely by chance rather than active hunting.


The coral-fish dynamic involves complex symbiotic and predatory relationships. While most corals do not actively hunt fish, some exceptions exist where corals like frogspawn will consume small fish. Fish feeding on coral is more common, with parrotfish and triggerfish as major coral predators. Maintaining balanced fish populations is crucial for the overall health of coral reef ecosystems. Further research and monitoring is needed to understand better these intricate connections on reefs like Australia’s Great Barrier Reef.