Clarkii Clownfish (Amphiprion clarkii)

What is a Clarkii Clownfish?

The Clarkii Clownfish (Amphiprion clarkii), also sold as Clark’s Anemonefish or the Yellowtail Clownfish, is the largest and arguably the most tenacious member of the Amphiprion genus. Where its cousins — the popular Ocellaris and Percula — have become the poster children of reef-keeping, the Clarkii has a longer track record as a working fish-keeper’s clownfish: hardier, more adaptable, and willing to use a wider variety of host anemones than any other species in the group.

Its colour pattern is bold and variable: a black body bisected by two or three brilliant white bars, with the tail and much of the fin margin washed in vivid yellow-orange. Some individuals, particularly those from the western Indian Ocean, are more orange overall; others — especially large females from Australian and Pacific populations — are intensely black with almost white bars. That variability is part of the species’ appeal.

At up to 14 cm (5.5 in) for a dominant female, the Clarkii is a substantial fish — roughly twice the body size of a fully grown Ocellaris — and it behaves accordingly. It is semi-aggressive: confident, curious, and quick to defend its chosen territory or anemone. That assertiveness is manageable in a thoughtfully stocked tank, but it is worth knowing upfront.

Where do Clarkii Clownfish come from?

Amphiprion clarkii has one of the broadest natural ranges of any anemonefish — from the Persian Gulf and Red Sea eastward through the Indian Ocean, across Southeast Asia, north to Japan, and south to northern Australia and New Caledonia. It is found on shallow coral reefs, reef slopes, and lagoon floors, almost always within the reach of a host anemone.

In the wild, Clarkii are typically found singly, in pairs, or in small groups dominated by a single breeding pair. They show strong site fidelity — the same pair will defend the same anemone for years. This territorial loyalty is the direct cause of the semi-aggressive temperament you will see in a home tank: the fish is not mean-spirited, it is simply very committed to its patch.

Nearly all Clarkii Clownfish sold today are captive-bred, which means healthier, hardier, pre-adapted-to-aquarium-food fish. Always choose captive-bred stock when available.

What size tank and setup does a Clarkii Clownfish need?

The minimum is 110 litres (29 US gallons) for a single fish or a bonded pair. Because the Clarkii is larger and more active than other common clownfish, that extra volume genuinely matters — a cramped tank amplifies territorial behaviour.

For setup, think mature reef or FOWLR:

• Established biological filtration is non-negotiable. A cycled tank with stable parameters is the single most important factor for any marine fish’s long-term health.
• Live rock provides hiding places, biological surface area, and the micro-organisms that supplement the Clarkii’s diet.
• A host anemone is optional but rewarding. If you plan to add one, upgrade to at least 150–200 litres: anemones need stable, pristine, well-lit water, and they wander until they find a spot they like. Bubble-tip anemones (Entacmaea quadricolor) are the easiest anemone to keep and a favourite host. Carpet anemones (Stichodactyla spp.) are also accepted, but they are large, delicate, and will eat small fish — experienced keepers only.
• Without an anemone, the Clarkii will readily adopt a large Toadstool leather coral, Hammer or Frogspawn LPS coral, or even a powerhead shroud as its proxy host. This behaviour is completely normal and harmless to robust corals.
• Flow and lighting should match whatever else is in the tank. The Clarkii itself is unfussy about flow direction.

What water parameters does a Clarkii Clownfish need?

Stable, mature reef chemistry is the goal:

• Salinity: 1.023–1.025 SG (specific gravity) — use a refractometer, not a swing-arm hydrometer, for accuracy. Evaporation raises salinity quickly in small tanks; top off with fresh RO water daily.
• Temperature: 24–27 °C (75–81 °F). Stability matters more than the exact number — swings above 29 °C or below 22 °C stress the fish.
• pH: 8.0–8.4. Easiest to maintain by keeping the sump or tank well-aerated; pH naturally dips overnight as CO₂ builds.
• Ammonia / Nitrite: 0 ppm at all times. The tank must be fully cycled before any fish is added.
• Nitrate: under 20 ppm for a fish-only tank, ideally under 5 ppm if you are keeping an anemone or delicate corals.
• Alkalinity / Calcium / Magnesium: standard reef parameters (8–11 dKH, Ca 400–450 ppm, Mg 1250–1350 ppm) if corals or anemones are present.

The Clarkii is more forgiving of parameter drift than many marine fish, which is a large part of why it is rated Easy. That said, every saltwater fish benefits from consistency — do not use the Clarkii’s hardiness as an excuse to skip water changes.

What do Clarkii Clownfish eat?

The Clarkii is a true omnivore and one of the easiest marine fish to feed. In the wild it grazes algae, picks at zooplankton, and scavenges scraps from its anemone host. In captivity it will accept virtually everything:

• Staple: high-quality marine pellets or flake (e.g., New Life Spectrum, Hikari Marine).
• Frozen: mysis shrimp, brine shrimp (enriched), Cyclops, and chopped clam or mussel are all eagerly taken.
• Supplemental: nori/seaweed strips, spirulina flake, and the occasional piece of raw shrimp or squid.

Feed small amounts two to three times daily — only what the fish can consume in under two minutes. Uneaten food rots and drives nitrate up, which is especially harmful if you are hosting an anemone.

Is the Clarkii Clownfish reef safe — and what can live with it?

Reef safe: Yes. The Clarkii will not pick at corals, clams, or clean-up-crew invertebrates under normal circumstances. The only caveat is the host anemone: carpet and other large Stichodactyla anemones actively sting and consume small fish and shrimp, so choose tank-mates carefully if you add one.

Good tank-mates:

• Peaceful reef fish that occupy different water columns — Dartfish (Firefish), Chromis (school them in groups of 5+), Cardinalfish, Blennies, and small Gobies all work well.
• Tangs in tanks 200 L+ are generally fine; the Clarkii will hold its territory and the Tang will stay out of it.
• Cleaner Shrimp (Lysmata spp.) and other ornamental shrimp are usually left alone.
• Clean-up crew — hermit crabs, turbo snails, and sea urchins are safe.

Avoid:

• Other clownfish species, or a second unrelated Clarkii adult — the dominant pair will harass intruders mercilessly.
• Very small, timid fish (tiny gobies, small dartfish in an established pair’s anemone territory) can be bullied.
• Large, aggressive fish like big Triggers, Lions, or Groupers that will simply eat the clownfish.

One pair per tank is the rule. Two juveniles introduced simultaneously will form a pair; introducing a third adult later almost always ends badly for the newcomer.

How do you tell male and female Clarkii Clownfish apart?

Amphiprion clarkii is a protandrous sequential hermaphrodite — every individual is born functionally male. In any social group, the largest, most dominant individual becomes (or remains) the breeding female; she cannot revert to male. If the female dies, the dominant male changes sex to replace her.

In practice: the female is simply and always the larger fish. In a bonded pair, the female may be 30–50% longer than the male. There is no reliable colour difference between sexes in this species, though breeding females may develop an even richer black body colouration over time.

If you buy two same-sized juveniles, the one that grows faster and eats more aggressively will become female.

How do Clarkii Clownfish breed?

Among marine fish, Clarkii Clownfish are genuinely straightforward to breed — one of very few marine species rated Easy in captivity. The process mirrors other Amphiprion species:

1. A bonded pair — established over weeks to months — begins spawning once both are mature (typically females at 2+ years, males slightly younger).
2. The male cleans a flat rock, tile, or the base of the anemone with meticulous attention. The female inspects and approves the site.
3. The female lays 200–500 bright orange eggs in a dense patch. The male immediately fertilises them.
4. The male guards and fans the clutch obsessively for 6–8 days, removing dead eggs and keeping the water moving. The female hovers nearby, defending the broader territory.
5. Eggs hatch just after dark on day 7 or 8. The tiny larvae are planktonic and must be reared separately in a dedicated larval-rearing vessel.
6. Larvae require rotifers for the first 7–10 days, transitioning to enriched Artemia nauplii and then to finely powdered dry food over the following 3–4 weeks.

Raising the larvae is the difficult part — not the spawning itself, which healthy, established pairs do readily. With practice and the right rearing setup, clutch-to-juvenile survival rates of 60–80% are achievable.

What are common Clarkii Clownfish health problems?

Marine fish share a core set of pathogens. Know these three:

• Marine Ich (Cryptocaryon irritans): white salt-grain spots on skin and fins, scratching behaviour, laboured breathing. The most common marine parasite. Hyposalinity (lowering SG to ~1.009 in a quarantine tank) is an effective, drug-free treatment; copper-based medications also work. The display tank must remain fish-free for at least 76 days at 26 °C to allow the parasite’s lifecycle to break without a host.
• Velvet (Amyloodinium ocellatum): a dusty gold or rust-coloured film, often most visible on the body at a raking angle. Velvet is far more dangerous than ich — fish can die within days. Treat aggressively with copper in a quarantine tank immediately.
• Brooklynella (“clownfish disease”): heavy, rapidly spreading grey mucus patches, especially on the gills; fish gasp and stop eating. Formalin baths in a hospital tank are the standard treatment. Captive-bred Clarkii are much less prone to Brooklynella than wild-caught fish.

Prevention is everything. Run a 4-week quarantine on all new fish before they enter the display tank. Most disease introductions are entirely avoidable.

The Clarkii’s robust constitution means it is less vulnerable than delicate species, but skipping quarantine remains the single biggest mistake new saltwater keepers make.

How long does a Clarkii Clownfish live?

A well-kept Clarkii Clownfish will live 10–18 years. Confirmed aquarium lifespans of 15+ years are well documented, and wild individuals in protected anemones have been observed for over 20 years. This is not a short-commitment fish.

That longevity is one of the species’ great appeals — a bonded pair, given a stable reef, pristine water, and a generous anemone, becomes a centrepiece that genuinely grows in character over the years. Invest in the right tank size and water quality from the start, and your Clarkii will reward you for a decade and more.