The Anemonefish: Icon of the Indo-Pacific Reef

Before I got into underwater photography, I kept a fairly large reef aquarium. One of the first fish I added was a mated pair of clownfish. Their bond, quirky behavior, and constant activity around their host anemone captivated me. That early fascination led me to breed clownfish—a challenging but rewarding pursuit. Years later, I find myself on dive trips across the Indo-Pacific, spotting their wild cousins on coral reefs from the Red Sea to Raja Ampat. And despite all the places I've been and species I've encountered, the anemonefish still holds a special place for me—both as a photographer and as someone who once raised them by hand.

A Family of Many Faces

Anemonefish, also known as clownfish, belong to the subfamily Amphiprioninae, which includes around 30 recognized species. The most well-known among them is Amphiprion ocellaris—popularized by a certain animated movie—but the family also includes A. clarkii, A. percula, A. frenatus, and the striking pink anemonefish (A. perideraion). These fish inhabit tropical reefs across the Indo-Pacific, from the Red Sea and East Africa to Polynesia, north to southern Japan, and south to Australia’s Great Barrier Reef.

Each species has preferred host anemones—large sea anemones with specialized stinging tentacles—and is generally found in relatively shallow depths, often less than 20 meters (66 feet), making them a common sight for recreational divers.

Life in a Tentacled Fortress

The relationship between anemonefish and sea anemones is one of the most iconic examples of marine symbiosis. It’s a textbook case of mutualism: both species benefit from the partnership. The anemone provides shelter and protection with its venomous tentacles, which deter predators that might otherwise prey on the small, slow-swimming fish. In return, the anemonefish defend their host from anemone-eating species like butterflyfish, aerate its tentacles with their constant fin movement, and may even feed it with leftover scraps.

The anemonefish’s protection from stings is due to a unique mucus coating on their skin. Unlike most fish, they don’t trigger the anemone’s stinging cells (nematocysts), and recent research suggests that this coating may be acquired gradually as juveniles acclimate to their host—rubbing themselves against the anemone in a slow, deliberate dance of acceptance.

Born Male, Becoming Female

Perhaps the most astonishing aspect of anemonefish biology is their reproductive system. All anemonefish are born male. Within each anemone-based social group, there’s a strict hierarchy: a dominant female at the top, her mate just below, and several subordinate non-breeding males. If the female dies, her mate undergoes a sex change and becomes the new female. The largest of the remaining males then becomes her mate. This sequential hermaphroditism ensures continuity within the anemone without needing new individuals to move in.

Breeding takes place on hard surfaces near the host anemone. The female lays hundreds—sometimes thousands—of eggs in a tight cluster. The male then fertilizes them and becomes their primary guardian. He fans the eggs constantly with his fins to oxygenate them and meticulously removes any that are diseased or dead. After 6–10 days (depending on water temperature), the larvae hatch and drift into the planktonic zone, where they face long odds before hopefully settling onto a reef and finding an anemone of their own.

Uninvited Guests: The Tongue Louse

Divers and aquarists alike may notice an unsettling sight in some anemonefish: a small crustacean peeking out from inside the fish’s mouth. This is Cymothoa exigua, also known as the tongue-eating louse. It’s an isopod parasite that attaches itself to the base of a fish’s tongue, eventually causing the tongue to atrophy. Remarkably, the louse then replaces the tongue’s function—anchoring itself in place and feeding on the host’s blood and mucus.

Although the parasite is most commonly documented in anemonefish in the Pacific, particularly around Papua New Guinea and the Philippines, it has a broad host range and is not exclusive to Amphiprion species. While the presence of C. exigua rarely kills the fish, it can affect feeding efficiency and overall health. It’s another reminder of the hidden challenges these fish face in the wild, far removed from the colorful innocence of their animated doppelgängers.

Dive Site Companions

Divers across the Indo-Pacific are likely to encounter anemonefish on nearly every reef. They are especially abundant in protected lagoonal environments and sheltered reef slopes. Locations like Raja Ampat, the Philippines, Papua New Guinea, Fiji, and the northern Red Sea are home to a high diversity of anemonefish species and their host anemones. Some, like Amphiprion clarkii, are generalists and can be found with many different host species, while others, like A. nigripes of the Maldives, are more selective.

Photographing Anemonefish

Photographers should approach slowly and with respect, as these fish—though tiny—are known for their bold territorial defense. They will often nip at a passing hand or camera lens if they feel threatened. Observing their behavior during a dive can be rewarding: look for egg clusters during the breeding cycle, or note the subtle size differences that reveal the social structure of a group.

For a more detailed article on how to capture these charismatic fish, check out Byron’s article Clownfish: The Ultimate Subject for Learning Macro Techniques.