More than just a cartoon fish, the common clownfish is one of the most popular marine species in the aquarium hobby. Often recommended for beginners, these hardy fish are full of character, but they still require the right setup and care before you bring your own "Nemo" home
Whenever a non-reefkeeper pictures a marine aquarium, chances are it contains a pair of common clownfish (Amphiprion ocellaris). And for good reason. Of all the marine fish available to aquarists, few are as instantly recognisable as these bright orange reef dwellers.
It is easy to assume their popularity stems entirely from Finding Nemo. While the film certainly introduced clownfish to a wider audience, they were already firmly established in the hobby long before Pixar's famous animation arrived. Their enduring appeal comes from a combination of vibrant colours, bold personalities and a reputation for being one of the hardiest and most forgiving marine fish available.
That does not mean they are suitable for every aquarium, however. Before you rush out and buy a pair for your new reef tank, it is worth taking a closer look at their requirements to make sure they are the right fish for you.
Related article: Beginner’s Guide to Reef Tanks: Choosing the Right Marine Aquarium
All photos by Shutterstock unless otherwise stated
Common Clownfish Fact File
Scientific name: Amphiprion ocellaris
Size: up to 10cm (4”) although males typically remain smaller than females.
Origin: Occurs in the Indo-Pacific.
Habitat: Found among host anemones in shallow reefs, most commonly associated with Radianthus magnifica, Stichodactyla gigantea, and S. mertensii.
Tank size: 60x35x30cm (24x14x12").
Temperament: Best kept as a pair. While generally peaceful, clownfish can be surprisingly territorial and dominant individuals may harass weaker tankmates, particularly in smaller aquaria. They are completely reef safe, although very small ornamental shrimp may occasionally be viewed as food by larger adults.
Feeding: Undemanding, readily accepting most live, frozen and dry foods.
Availability & cost: One of the most widely available marine fish, stocked by almost every retailer selling saltwater livestock. Standard specimens typically cost around £20 each, while designer strains can command considerably higher prices.
Common Clownfish in the Wild
The common clownfish is found throughout the tropical Indo-Pacific, inhabiting shallow coral reefs from north-western Australia to the Ryukyu Islands of southern Japan. Here, they spend much of their time amongst the stinging tentacles of host sea anemones. They are most commonly associated with the magnificent anemone (Radianthus magnifica), giant carpet anemone (Stichodactyla gigantea) and Mertens' carpet anemone (S. mertensii).
Radianthus magnifica
This relationship is perhaps the most famous example of symbiosis in the marine world: a partnership that benefits both parties. The clownfish gains protection from predators by sheltering amongst the anemone's tentacles, while the anemone benefits from additional nutrients provided by fish waste and scraps of food.
It is this hosting behaviour that makes clownfish such a good option for beginners. Despite growing to around 10cm (4in), they rarely venture far from their chosen home, meaning they can be housed in smaller aquaria than many other fish of a similar size. We'll look at their aquarium requirements in more detail later.
While clownfish may look cute and harmless, they are fiercely protective of their territory. Divers know this all too well, often receiving a sharp nip from an angry clownfish after venturing too close to its anemone.
Social Behaviour
On tropical coral reefs, common clownfish often live in small groups, sharing a host anemone. Within these groups there is a strict social hierarchy, headed by a dominant female. She is the largest fish in the group and is usually easy to identify.
The second-largest individual is the breeding male, while any remaining fish are sexually immature males. There are no immature females because all clownfish are protandrous hermaphrodites, meaning they begin life as males and can later change sex.
The dominant pair maintain their position through persistent aggression towards subordinate fish, helping to preserve the group's social structure. Should the female die, however, the breeding male undergoes a sex change and becomes female. The next-largest fish in the hierarchy then matures into the new breeding male.
This unusual system allows clownfish groups to continue breeding even when one member of the dominant pair is lost, and helps explain why keeping multiple clownfish together in smaller aquaria can often end in conflict.
Aquarium Clownfish Care
So, how does their natural biology influence how we keep common clownfish in our marine aquariums? Well, let's break it down into bitesized sections.
Water Parameters
As we established earlier, common clownfish are found on tropical coral reefs. These environments are remarkably stable, providing us with a useful blueprint for creating suitable conditions in the aquarium.
Fortunately, unlike some of the more demanding reef inhabitants, clownfish are relatively hardy and can tolerate a wider range of conditions than many marine species. This is especially true of the tank-bred fish that dominate the hobby today, many of which have been raised in captivity for generations.
Measure specific gravity and/or salinity with a refractometer.
Aim for the following water parameters:
- Temperature: 24-27°C (75-81°F)
- Salinity: 30-35ppt
- Specific Gravity: 1.023-1.026
- pH: 8.1-8.4
- Alkalinity: 7-11dKH
While these values provide a useful target, stability is ultimately more important than chasing exact numbers. Sudden swings in temperature, salinity or pH are far more likely to cause problems for clownfish than maintaining values slightly outside the ideal range.
As with all livestock, both ammonia and nitrite should be kept at 0ppm. Despite their reputation for being hardy, clownfish should never be used to cycle a new aquarium. Instead, establish the biological filter beforehand using live rock or bacterial products and a suitable ammonia source, such as ammonium chloride, before introducing any livestock.
Related article: How do I cycle my new nano reef tank?
Minimum Tank Size
Common clownfish grow surprisingly large, particularly the females. On more than one occasion I have heard hobbyists point at a mature female that has been returned to a fish shop and ask what species it is, convinced it cannot possibly be a common clownfish.
Although they spend much of their time hovering around a chosen territory, a fully grown clownfish is still a 10cm (4in) fish and needs adequate space. For long-term care, the absolute minimum aquarium I would consider is one measuring 60cm (24") in length.
That said, a mature female can look rather imposing in a tank of this size. While they may survive and even breed in smaller aquaria, that does not necessarily mean it is the best environment for them.
As is often the case in fishkeeping, bigger is better. If you can stretch to a 90cm (36") aquarium, I think you'll be glad you did. The additional water volume provides greater stability, gives the fish more room to establish territories and opens up a far wider range of compatible tank mates.
A larger aquarium also allows you to create a more natural reefscape, making for a more interesting display and a more engaging aquarium to watch over the long term.
Clownfish Compatibility
In the vast expanse of a coral reef, groups of clownfish coexist successfully. There are usually enough subordinate fish to spread out the dominant pair's aggression, and weaker individuals can simply move away when tensions rise.
Indeed, the magnificent, or ritteri, anemone that common clownfish often associate with can grow to over 50cm (20") in diameter. That's a lot of space for a group of clownfish to coexist and is something very difficult to replicate in an aquarium.
In larger aquariums, housing groups of clownfish can be successful, indeed you'll often see such a tank at public aquariums, but at home it is generally best to keep just a bonded pair.
The easiest way to achieve this is by purchasing two juveniles. As they mature, the larger fish will become female while the smaller fish remains male. Pairing mature fish is far less predictable and can sometimes result in persistent aggression.
Good Tank Mates
There are plenty of fascinating fish that you can keep alongside clownfish, as well as corals and other invertebrates too. With clownfish showing some territorial aggression, it is best to opt for fish that occupy different areas of the tank. Gobies work great, and there are plenty of species to choose from.
Small coral gobies like to perch on the rocks and corals, and their smaller size makes them better suited for tanks of 60cm (24") in length. Larger yellow watchman gobies (Cryptocentrus cinctus), pictured above, have characterful faces and dig burrows in the substrate, staying clear of the clownfish.
Related article: Special Relationships: keeping pistol shrimps and gobies.
Blennies are another great option, full of personality. They love to perch all over the tank, and species like the tailspot (Ecsenius stigmatura), flymo (Blenniella chrysospilos), and algae blennies (Salarias fasciatus) graze on hair algae, contributing to the clean-up crew of your reef tank. Tailspots stay small, while algae blennies are chunkier and more suited to tanks of 90cm (36") or larger.
Cardinalfish, firefish, royal grammas and smaller reef-safe wrasses all make excellent options as well.
Flame angelfish
In larger tanks of at least 90cm (36"), dwarf angelfish from the Centropyge genus can also work well. However, they're not totally reef safe and can nip coral mantles and LPS hard corals.
Larger again, in tanks of 120cm (48") some of the smaller tangs and anthias start to become viable options to choose from.
Add with Caution
Other territorial fish can coexist with clownfish if sufficient territories are available. However, catching and removing a problematic fish from a mature reef aquarium can be a frustrating experience, so choose carefully.
Damselfish – a close relative of the clownfish, these are similarly feisty. They have a reputation for being hardy and cheap resulting in beginner reefkeepers adding them first and regretting it later. More peaceful species such as the azure damselfish (Chrysiptera hemicyanea) and green chromis (Chromis viridis) can work well, particularly in larger aquaria. In tanks smaller than 90cm (36"), it is usually best to keep just a single specimen
Dottybacks – Territorial by nature, dottybacks are quick to defend their favourite hiding place and rarely back down from confrontation. This can create problems when housed with an equally stubborn clownfish pair. If you wish to keep one, the orchid dottyback (Pseudochromis fridmani), pictured below, is from the Red Sea and is generally among the more manageable choices.
Six-line wrasse – This species has been split out from the other small wrasses, as they are notorious for becoming aggressive in smaller tanks when they mature. Rarely will they cause too many issues for the clownfish themselves, but if you want a peaceful reef, I'd steer clear of this beautiful wrasse and stick to one of the more peaceful options.
Shy, peaceful and slow-feeding species may also struggle alongside established clownfish. While they can be kept successfully in spacious aquaria with plenty of hiding places, beginners may find them difficult to manage.
Dragonets – Including mandarins and scooter dragonets, these beautiful fish are infamous for starving in poorly prepared aquaria. They require mature systems with abundant populations of live copepods and enough space to avoid more boisterous tankmates.
Pipefish – Slow-moving and deliberate feeders, pipefish are not ideal candidates for a busy community reef. That said, experienced aquarists can achieve excellent results with species such as the blue-striped pipefish, provided their specialised feeding requirements are met.
Species to Avoid
Large predatory fish should be avoided entirely. Most require significantly larger aquaria than those recommended for common clownfish anyway.
As a general rule, if a fish can fit a clownfish in its mouth, there is a good chance it will eventually try. It simply isn't worth the risk.
Related article: Marine fish with character.
Snowflake eels, for example, are often considered more of a threat to crustaceans than fish, but a large adult is certainly capable of taking a clownfish if given the opportunity. Lionfish, groupers and many triggerfish should also be excluded from a clownfish aquarium.
Similarly, larger puffers are generally poor companions. While some species may initially ignore clownfish, their eventual size, powerful jaws and opportunistic feeding habits make them an unnecessary risk in the long term.
Feeding Common Clownfish
Feeding common clownfish is refreshingly straightforward. Unlike some marine fish that require specialised diets or live foods, clownfish are opportunistic omnivores and will readily accept a wide variety of foods.
In the wild, they spend much of the day picking at zooplankton drifting past their host anemone, alongside small crustaceans and algae. Rather than hunting large prey items, they are constant grazers, taking advantage of whatever the reef currents deliver, and gorging themselves when food is in an abundance.
Most captive-bred clownfish will eagerly accept high-quality marine pellets and flake foods, making these an excellent staple diet. Supplement these prepared foods with frozen offerings such as Mysis shrimp, enriched brine shrimp, copepods and finely chopped krill.
Photo by Alex Bell
Like many small reef fish, clownfish naturally feed throughout the day. Therefore, they benefit from smaller, more frequent meals rather than a single large feeding. Two to three feeds per day is ideal.
One of the few mistakes beginners make is overfeeding. Clownfish always seem hungry and will enthusiastically beg for food whenever someone approaches the aquarium. Resist he temptation to give in. Excess food quickly contributes to declining water quality, nuisance algae growth, and potential health problems.
A healthy clownfish should be alert, active and well-rounded through the body without appearing bloated.
Do Clownfish Need an Anemone?
In short, no. Common clownfish do not require an anemone to thrive in the aquarium. In fact, many of the clownfish available in the aquarium trade today have been captive-bred for generations and may have never encountered an anemone before.
This often comes as a surprise to newcomers, many of whom assume that keeping clownfish and anemones together is essential. While it can make for a stunning display, anemones are generally far more demanding than the clownfish themselves.
Instead, clownfish frequently adopt alternative hosts in the aquarium. Some take up residence amongst the polyps of corals, while others choose less conventional homes such as magnetic algae scrapers, powerheads or even a favourite corner of the hardscape.
If you would like your clownfish to host a coral, species with long, flowing polyps tend to work best. Euphyllia (torch corals) and Fimbriaphyllia (hammer and frogspawn corals), long-polyp toadstool leathers and Xenia are all popular choices. Although Goniopora may look like the perfect substitute, their greater sensitivity means they are often unsuitable for beginner reef tanks.
Related article: Back to saltwater: starting simple with beginner corals.
If you have your heart set on keeping an anemone, be prepared to do plenty of research first. They require stable water conditions, appropriate lighting and careful placement within the aquarium. For most hobbyists, the bubble-tip anemone (Entacmaea quadricolor) is the best place to start. While it is not a natural host for common clownfish, many individuals will readily adopt one in captivity.
Don't be disappointed if your clownfish ignores its anemone. Some fish take months to move in, while others never show any interest at all.
Related article: Keeping anemones in the reef aquarium.
Breeding Common Clownfish
Breeding marine fish is a challenge that scares off many hobbyists. The drifting larval stage that many marine fish go through makes them far more difficult than many of the freshwater fish.
Clownfish are one of the best options for those wanting to try marine fish breeding. Indeed, an established pair may spawn in your display aquarium without you doing anything more than providing a stable home and quality food.
The first sign of spawning occurring is usually heightened territorial aggression as well as both fish spending more time cleaning a small patch of rock within their territory.
The female then lays hundreds of bright orange eggs, which the male then fertilises. The pair work together to care for the developing clutch, fanning the eggs with their fins and removing any infertile or damaged eggs.
Over the following week, the eggs gradually darken as the developing embryos grow inside. Shortly before hatching, it is often possible to see the silver eyes of the young fish through the egg casing.
In most reef aquaria, the larvae hatch after around seven to ten days, usually shortly after the aquarium lights switch off. Unfortunately, these tiny larvae won't survive in community aquaria, as they are quickly consumed by filtration equipment, corals and other tank inhabitants.
Successfully raising clownfish requires a dedicated rearing system, specialised live foods and a significant amount of preparation. While they are one of the easiest marine fish to breed and raise, it is generally considered an advanced project within the marine fishkeeping niche.
Even if you have no intention of raising the fry, watching the spawning behaviour within your slice of a coral reef is certainly fascinating.
Related article: How to set up a marine fish room for breeding.
Common problems and FAQs
As this is often one of the first marine fish people keep, there's a few common questions new reefkeepers ask.
What is the difference between an ocellaris clownfish and a percula clownfish?
The common clownfish (Amphiprion ocellaris) and percula clownfish (Amphiprion percula) look very similar and are often confused. In general, percula clownfish have thicker black markings around their white bars and more orange in the eyes, while ocellaris clownfish tend to have thinner black edging and darker eyes. Also, ocellaris typically have eleven, but sometimes ten, dorsal spines while percula clowns usually have ten or sometimes nine.
The bright orange eye suggests that this is a percula clownfish, but it has thin black lines around the white markings.
For most aquarists, the differences are largely cosmetic. Their care requirements, behaviour and suitability for reef aquariums are almost identical, making either species an excellent choice for beginners.
Why are my two clownfish always fighting?
Some level of aggression is completely normal when two clownfish are establishing a pair. The larger fish will become the dominant female, while the smaller fish takes on the role of breeding male. During this process, chasing, nipping and displays of dominance are common.
Provided the smaller fish is still feeding and not showing signs of injury, this behaviour is usually nothing to worry about and often settles down after a few weeks.
If, however, you purchased two large individuals from different tanks, there's a chance that you have two females, or at least two fish that have begun to change into females. This change is irreversible and they will never pair up.
I lost one of my established clownfish, how do I introduce a new one?
When replacing a lost clownfish, many aquarists assume they should buy a new fish of a similar size. With clownfish, however, this can create problems.
Instead, it is usually best to introduce a small juvenile. Young clownfish readily assume the role of subordinate male, allowing the established fish to remain dominant. This greatly reduces the likelihood of serious aggression and increases the chances of forming a successful pair.
Keep a close eye on the fish during the first few days. Some chasing and displays of dominance are normal, but the newcomer should still be able to feed and find shelter. If aggression becomes relentless, temporary separation may be required.
Why won't my clownfish use its anemone?
One of the most common disappointments amongst clownfish keepers is buying an anemone only for the fish to completely ignore it. Unfortunately, there are no guarantees when it comes to hosting behaviour.
Some clownfish move into an anemone within minutes, while others may take months or never show any interest at all. Captive-bred clownfish are particularly unpredictable and may instead choose another area of the tank as their home. It is also worth checking that the anemone species you have chosen is a natural host, as clownfish are generally more likely to adopt compatible species.
Over the years, hobbyists have come up with all sorts of tricks to encourage hosting behaviour. One of the most popular involves showing videos of clownfish living in anemones to the fish. While some aquarists swear by this method, it may just be that they simply decided it was time to move in, leaving the reefkeeper convinced their training programme had been a success.
Final thoughts
There is a reason the common clownfish remains one of the most popular marine fish in the world. Hardy, colourful and packed with personality, few species are as well suited to introducing aquarists to the rewards of reefkeeping.
Their popularity can sometimes work against them, leading experienced hobbyists to overlook them in favour of more unusual species. Yet a healthy, established pair of clownfish remains one of the most engaging sights in any reef aquarium, whether they are tending a clutch of eggs, defending their chosen territory or simply hovering amongst the corals or anemone that they call home.
Provide them with a mature aquarium, suitable tank mates and a varied diet, and common clownfish can live for well over a decade. They may not be the rarest fish in the shop, but they have earned their place as a reefkeeping classic.