Anemonefish: The Clownfish of Indonesia’s Coral Reefs
Anemonefish are the small, brightly coloured reef fish that live among the stinging tentacles of sea anemones, and they are one of the best-loved sights in the marine wildlife of Indonesia. Many people know them as clownfish from films and aquarium displays, but the fish in Indonesian waters live in the wild in dense colonies, each one tied to a single anemone. Their orange, white and black bands catch the light as they dart between the anemone’s tentacles, and they are among the first fish that most snorkellers and divers learn to recognise. The anemonefish of Indonesia belong to a reef system of extraordinary richness, and watching them is a good introduction to how coral reefs work.
What the Anemonefish Looks Like
Anemonefish are compact fish with rounded bodies and bold patterns. Most species show white bands edged with black against an orange or red body, and the bands are one of the easiest ways to identify the group. The fins are short and rounded, which helps the fish move with precision among the anemone’s tentacles. Their colours are strong enough to be seen from a distance in clear water, and the contrast between the fish and the anemone makes them easy to follow.
Size is modest. Most anemonefish reach only a few centimetres in length, and the largest species are not much bigger. Their small size makes them vulnerable to predators, and it also means that the health of their anemone home is crucial to their survival.
Species and Variety
Indonesian waters hold several species of anemonefish, and they differ in the number and shape of their bands, the colour of their bodies and the anemones they choose. Some species live on only one kind of anemone, while others use several. The variety reflects the many reef systems of the archipelago, from the shallow lagoons of the east to the deep channels of the west.
Where the Anemonefish Lives
Anemonefish live in shallow coral reefs and reef flats across the Indo-Pacific. Indonesia lies at the heart of this region, and its reefs are among the most diverse in the world. The fish are found on the reefs around Java, Bali, Sulawesi, the Lesser Sunda Islands and the Maluku group, and each area has its own mix of species and anemones.
The reefs that hold anemonefish are often close to shore, where the water is warm and clear. Divers and snorkellers find them on the reef tops, in lagoons and at the edges of channels. The fish stay close to their anemone for their whole lives, and they rarely move far from the shelter of its tentacles.
Protected Reefs and Good Places to Look
Marine parks protect many reefs where anemonefish can be seen in good health. The coral reefs of Bali offer a good introduction to the reef systems of the wider region, and the Komodo National Park protects reefs that hold many species of fish, invertebrates and coral.
The Partnership With the Anemone
The relationship between an anemonefish and its anemone is one of the best-known examples of mutualism in the sea. The anemone’s tentacles carry a sting that deters most predators, and the fish is protected by them. In return, the fish cleans the anemone, removes debris and provides nutrients through its droppings. Some species of anemonefish even chase away butterflyfish and other creatures that might eat the anemone.
The fish also appear to be immune to the sting of their anemone. They develop a protective layer of mucus that prevents the tentacles from firing, and they learn to move through the tentacles without being stung. This adaptation takes time, and young fish must be introduced to the anemone carefully to become accepted.
Living in a Group
Each anemone often hosts a small group of fish, with a dominant female, a male and a number of smaller juveniles. The female is the largest and most aggressive, and she controls the group. If the female dies, the largest male changes sex and takes her place, which allows the group to continue. This social structure is one of the most fascinating parts of the anemonefish’s life.
Behaviour on the Reef
Anemonefish are territorial and defend their anemone from rivals. They chase intruders, nip at them and display their bright colours to warn others away. The defence is most intense during the breeding season, when the pair guards a patch of nesting material close to the anemone.
Breeding is an intimate affair. The male cleans a flat area of rock near the anemone, and the female lays eggs on it. The male guards the eggs until they hatch, fanning them with his fins to keep them clean and oxygenated. Once the young hatch, they drift into open water and must find an anemone of their own to survive.
Dispersal and Settling
Young anemonefish spend a short time drifting in the plankton before they settle on the reef. They must find a suitable anemone within a few days, or they perish. This stage of life is one of the most dangerous, and only a small fraction of the young survive to adulthood.
Threats to the Reef Fish
Anemonefish face several threats. Coral bleaching caused by rising sea temperatures damages the reefs that host the anemones, and the loss of anemones leaves the fish without homes. Destructive fishing practices, including the use of explosives and cyanide, have caused serious harm to reef systems across Indonesia, and the collection of anemonefish for the aquarium trade has reduced populations in some areas.
Pollution from coastal development, sediment from land clearance and damage from anchors and divers also affect the reef. Protecting these systems requires marine parks, careful management of tourism and the enforcement of rules against destructive fishing.
Responsible Reef Visiting
Do not touch anemones or fish, do not stand on the reef and avoid kicking up sediment. Use reef-safe sunscreen, and choose operators who follow the rules of the marine park. Never buy aquarium fish taken from the wild, since this trade damages the reef.
Seeing Anemonefish on a Reef Visit
The easiest way to see anemonefish is on a shallow snorkel or dive over a healthy reef. Look for anemones in sandy patches and on the reef flats, and watch for the fish sheltering among the tentacles. Move slowly and keep your hands and fins away from the reef, because contact can damage both the coral and the anemone.
Visibility varies with the season and the weather. Calm mornings often provide the clearest water, and a guide who knows the reef will be able to point out the best anemones and explain the behaviour of the fish.
Preparing for a Snorkel
Bring a mask that fits well, a snorkel, a rash vest for sun protection and a waterproof camera if you wish to photograph the fish. Carry water and a hat for the boat ride back. Stay with your group and follow the instructions of the crew at all times.
Why the Anemonefish Matters
The anemonefish is a symbol of the partnership that keeps coral reefs alive. Its relationship with the anemone shows how species depend on each other, and its presence tells observers that the reef is healthy enough to support a complex community. Protecting the anemonefish means protecting the reef, the anemones and the wider community of fish and invertebrates that call it home.
Visitors who want to learn about the broader marine life of the region can read the sea turtles of Bali page, which describes another animal that depends on healthy reefs and clean coastal waters.
Choosing an Anemone Home
Not every anemone suits every fish, and the choice of host matters a great deal. Some species of anemonefish live only in one kind of anemone, while others move between several. A young fish that cannot find a suitable anemone may spend days in open water, where it is highly exposed. Once settled, a fish may stay in the same anemone for its whole life unless the anemone is damaged or removed, and a healthy anemone is therefore worth a great deal to the fish that depend on it.
Anemones can be damaged by careless divers, by boat anchors and by waves from storms. Their recovery is slow, and the fish that live in them must wait for the host to regrow. Protecting anemones is one of the simplest ways to protect the fish that rely on them.
Cleaner Fish and Reef Health
Anemonefish belong to a wider group of reef residents that depend on clean, healthy coral. When a reef is damaged, the number of anemones falls, and with them the homes of the fish. The loss travels up the food chain, because the same reef shelters many other species that feed on algae, plankton and small invertebrates. Watching a group of anemonefish in good condition is therefore a quick way to judge whether a reef is recovering from past damage.
Related guides: spiny lobster, bryde's whale, Tasselled Wobbegong in Indonesia, epaulette shark, Reef Fish Feeding Roles: Who Eats What on Indonesian Reefs.