Saltwater Fish · Clownfish
Ocellaris Clownfish
Amphiprion ocellaris
Hardy, beginner-friendly reef-tank clownfishBeginner
- Lifespan
- 10-20+ years
- Size
- 3-4 in7-11 cm; female larger
- Social needs
- Solitary or bonded pair; not a shoaling fish
- Time
- Daily feeding; weekly water testing/changes
- Cost
- High
- Diet
- Omnivore (marine pellets, frozen, algae)
Overview
What is this animal?
- The Ocellaris is the orange-and-white clownfish often called "Nemo" and is a good marine fish for beginners.
- Most stock sold today is captive-bred, which makes it hardy, adaptable to aquarium foods, and less prone to disease than wild-caught fish.
- It is also among the milder-tempered clownfish.
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- It does not need a host anemone to thrive, which is helpful because anemones are demanding and better suited to experienced keepers.
- A single fish or a bonded pair works well.
- Its bold, personable behaviour makes it a watchable centrepiece.
Temperament
- Ocellaris are peaceful by clownfish standards and reef-safe, generally ignoring corals and most tankmates.
- A bonded pair forms a hierarchy, with the larger fish becoming female; all clownfish begin as males and the dominant one changes sex.
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- They can be mildly territorial around their chosen spot but rarely cause real trouble.
- Keep only one fish or one bonded pair, since two unbonded clownfish, especially of different species, often fight.
- They make confident, interactive display fish.
A good fit for
- First-time marine aquarium keepers
- Reef tanks (reef-safe)
- Keepers wanting a hardy centrepiece
- Captive-bred ethical purchasers
Common mistakes to avoid
- Adding fish to an uncycled tank
- Assuming they need an anemone to survive
- No lid - clownfish jump
- Housing two unbonded clownfish that fight
Enclosure
Minimum 79 gallons300 litres
Fine alone or with company. Solitary or bonded pair; not a shoaling fish
- A cycled tank of at least 80 gal300 L, 3 ft90 cm or more from end to end, suits a single fish or a bonded pair, with live rock for territory and a tight-fitting lid since clownfish can jump.
- Maintain salinity 1.024-1.026, temperature 75-80°F24-27°C, pH 8.1-8.4, with ammonia and nitrite at zero and nitrate below 20 ppm.
- Add fish only to a fully nitrogen-cycled system; new tanks need several weeks to establish beneficial bacteria.
- Stable parameters matter more than perfect ones, so use a reliable heater, a powerhead for flow, and a quality test kit.
Supplies
Setup
- Tank, stand and sump, about 80-90 US gallons300-340 litres
- Return pump and powerheads
- Protein skimmer
- Reef lighting
- Rock and sand
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- Salt mix, refractometer and test kits
- Quarantine tank
Ongoing
- Quality small marine pellet
- Frozen mysis shrimp
- Frozen enriched brine shrimp
- Algae-based marine flake
- Vitamin or HUFA soaking supplement
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- Small thawing cup and strainer
- Turkey baster for target-feeding
Safe substrate: Aragonite sand · Dry or cured live rock
Care routine
Daily
- Check salinity, temperature and flow
- Feed small marine portions
- Head-count and look everyone over
- Top up evaporation with fresh water
Every few days
- Service the skimmer and filter socksevery 3 days
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Weekly
- Clean the glass
- Test the water
- Watch the pair's pecking order
- Water change
Monthly
- Calibrate the refractometer
- Check salt, RO/DI and reagents
Less often
- Deep-clean pumps and powerheadsevery 3 months
- Replace RO/DI filter mediaevery 6 months
Health review: Quarterly review with a pair check, every 3 months
Tools
Care in depth
Diet
Omnivore (marine pellets, frozen, algae)
- Ocellaris are omnivores.
- Offer a quality marine pellet or flake as a staple, supplemented with frozen mysis and brine shrimp and occasional algae-based foods.
- Feed small amounts once or twice daily, only what the fish finish in a couple of minutes, to keep nitrate low.
- Captive-bred fish accept prepared foods readily, so weaning is rarely an issue.
- Vary the diet for colour and immune health, and soak frozen foods in a vitamin supplement now and then.
- Avoid overfeeding, the most common cause of poor water quality.
Health
Signs of good health, and the common problems
- Clownfish are robust but susceptible to marine ich (Cryptocaryon) and Brooklynella (nicknamed "clownfish disease", though it infects many other marine fish too) if stressed or kept in poor water.
- Quarantining new arrivals and maintaining stable salinity and temperature prevent most outbreaks.
- Watch for rapid breathing, scratching against rock, or white spots, which signal parasites.
- Good filtration, regular water changes, and a varied diet support the immune system.
- Captive-bred stock generally ships healthier than wild-caught fish.
- With stable water and good food an Ocellaris commonly lives well past 10 years; captive fish have been recorded alive at 22 and still spawning past 20, so plan for a 15-20 year commitment.
Is this urgent?
6 warning signs and how fast to act, 3 of them right away
In a reef, stability matters more than any single target number. A parameter moving fast does more damage than a parameter sitting slightly off.
Go now
Any detectable ammonia or nitriteWater change now with matched, mixed and aerated saltwater. Stop feeding. Ammonia is directly toxic, and at reef pH more of it is in the toxic form, so a marine system has less margin than a freshwater one. Nitrite is far less toxic in seawater, but any reading in a stocked tank means the biological filter is not keeping up.
NowTemperature or salinity has moved sharplyCorrect slowly, over hours, not minutes. Check the heater and the top-off. The speed of the change does the damage. Correcting fast repeats the injury in the other direction.
NowRapid gilling, or a fish hanging in the flow breathing hardIncrease aeration and check temperature and salinity. Warm water holds less oxygen, and a heater failure shows up here first.
NowToday
White spots, or a fine dusting like icing sugarIdentify which parasite before treating. Most reef tanks cannot be treated in place. The two common parasites look similar and need different handling; velvet can kill a tank in days.
TodayCorals closed for more than a day, or receding tissueTest alkalinity first, and compare it against the last reading rather than a target. Unstable alkalinity is the most commonly cited coral killer, and a swing shows up in the trend, never in a single point.
TodayA new fish added without quarantine now looks unwellRemove it to a separate system today if you can. Nearly every wipeout in a reef tank traces back to a skipped quarantine.
TodayQuarantine every new animal, including corals and inverts. It is the single practice that separates a reef that lasts from a reef that restarts.
This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it, and the time to find one is before you need one.
Bedding and substrate
2 safe, 3 with a caveat, 2 to avoid
In a marine system the rock and the sand are life support, and how you start them decides the first six months.
Safe
Aragonite sandThe standard marine substrate, and it hosts the biology. It does not meaningfully hold pH or alkalinity at normal reef pH, so test and dose for those regardless.
safeDry or cured live rockDry rock avoids importing pests but takes longer to mature. Cured rock is faster and riskier.
safeWith a caveat
Deep sand bedsPowerful nutrient processing when they work and a sulphide release when they are disturbed. Choose shallow or deep deliberately, not by accident. A sand-sifting or burrowing goby needs a fine bed about 2 to 3 in5 to 8 cm deep that it turns over itself. That is a different thing from a denitrifying deep sand bed (4 in10 cm or more, left undisturbed), and the two do not mix: a sifting goby disturbs the layers a deep sand bed depends on and eats the life in it.
with a caveatUncured live rockIt will cycle the tank for you, and it will also bring in whatever was living in it.
with a caveatBare bottomWorkable in high-flow systems for fish that neither sift nor burrow, but it removes a large part of the biological buffer. Wrong for watchman gobies and other gobies that burrow or sift, which need a fine sand bed at least 2 in5 cm deep to dig and feed in, and for mandarins and other copepod-eaters, which need sand as well as mature rock for their food to breed in.
with a caveatNever
Silica play sandNot the marine standard, and commonly blamed for feeding diatom blooms in a new tank.
neverAny rock or decor of unknown originMetals and phosphate leach for months and are almost impossible to trace once the tank is running.
neverThis is our general list for saltwater fish. We have not built one specific to Clownfish yet.
Top resources for more info
Independent creators and organisations we would send a friend to. We have no affiliation with any of them, and nothing here is sponsored. Links checked 2026-10-22.
YouTubers
HumbleFish & ReefSaltwater fish disease, quarantine and treatment (Humble.Fish forum)BRStvReef tank setup, fish health and quarantine series (run by a retailer)FishOfHex AquaticsBeginner saltwater guides, avoiding common mistakes and tank disasters
Sites
Keep going
Clownfish, side by side
Same axes, same care guides: the honest way to choose between types.
