Marine fish profile: Clownfish

Say the word clownfish to someone, anywhere in the world, and they’ll know what you’re talking about. Clownfish, or anemonefish, to use their proper name, shot to mainstream fame in 2003 with Disney’s Finding Nemo animation, but to naturalists and us fishkeepers, they were famous way before, and for lots of other reasons. 

Clownfish found fame first of all for their choice of residence – anemones. Obligate symbionts, all 30 species of clownfish in a 12,000-mile range from the Red Sea to the Indian Ocean, to the Pacific ocean, all live in anemones. No exceptions. There are over 1000 anemone species but just 10 host all 30 clownfish species. We love that clownfish make homes in anemones and we love their cute looks, small size, bright colours, and their slow, paddling, wavy swimming pattern. They’re a saltwater aquarium hit.

The sting

The clown and anemone symbiosis are mutually beneficial. The stinging cells of the anemone protect clownfish from large, predatory fish, and the clownfish, in turn, protect the anemones from Butterflyfish, who don’t mind the stinging defences and dine on them. Anemones also benefit from the extra aeration and nourishment from clowns, and many a captive clown and “nem” keeper will observe a clownfish feeding its anemone host, and even clearing the area around it of algae and rival coral growth.

There is no consensus on why the clownfish doesn’t get stung by the anemone. Some theories are that the fish’s mucus camouflages it against the anemone. Others are that the fish smear themselves with the anemone’s own mucus, making them invisible. One hypothesis said that clowns had neutral mucus, where other fish had acid mucus. Another said that clownfish mucus thickened upon contact. 

One train of scientific thought was that clowns could customise mucus chemistry to decrease the synthesis of substances which excite the anemone’s nematocyst discharge. Another was that clownfish mucus is based on sugars rather than proteins, and lastly, that clownfish are just naturally immune to anemone stings, though this has been disproved. 

Whatever it is, the anemonefish/anemone mutual relationship is obligate, and science has proved that Clownfish do not survive in the wild without anemones, and for the 10 host anemone species, they cannot survive without clownfish. Which makes you think a bit more about the effects of wild collection…if one were collected without the other…the organism left behind would face death if a new localised pairing could not be made, and fast. 


There are 30 clownfish species within the subfamily Amphiprioninae, and that subfamily lies within the family Pomacentridae, which also contains the damselfish. Amphiprioninae then splits into two genera, the monotypic Premnas – the Maroon clown, Premnas biaculeatus, and the rest are in Amphiprion. They can then be divided further into six complexes – Percula, Tomato, Skunk, Clarkii, Saddleback and Maroon. The Percula clown complex includes the Common clown, Amphiprion ocellaris, and the Percula clown, Amphiprion percula, and together those two species are the biggest selling and most kept marine fish on the planet. Nemo was a Common clown.

All 30 described clownfish species

  1. Amphiprion akallopisos, Skunk clownfish
  2. Amphiprion akindynos, Barrier reef anemonefish
  3. Amphiprion allardi, Twobar anemonefish
  4. Amphiprion barberi, Fiji barberi clownfish
  5. Amphiprion bicinctus, Two Band anemonefish
  6. Amphiprion chagosensis, Chagos anemonefish
  7. Amphiprion chrysogaster, Mauritian anemonefish
  8. Amphiprion chrysopterus, Orange Fin anemonefish
  9. Amphiprion clarkii, Yellowtail clownfish
  10. Amphiprion ephippium, Saddle anemonefish
  11. Amphiprion frenatus, Tomato clownfish
  12. Amphiprion fuscocaudatus, Seychelles anemonefish
  13. Amphiprion latezonatus, Wide-band Anemonefish
  14. Amphiprion latifasciatus, Madagascar anemonefish
  15. Amphiprion leucokranos, Whitebonnet anemonefish
  16. Amphiprion mccullochi, Whitesnout anemonefish
  17. Amphiprion melanopus, Fire clownfish
  18. Amphiprion nigripes, Maldive anemonefish
  19. Amphiprion ocellaris, Clown anemonefish
  20. Amphiprion omanensis, Oman anemonefish
  21. Amphiprion pacificus, Pacific anemonefish
  22. Amphiprion percula, Orange clownfish
  23. Amphiprion perideraion, Pink anemonefish
  24. Amphiprion polymnus, Saddleback clownfish
  25. Amphiprion rubrocinctus, Red Anemonefish
  26. Amphiprion sandaracinos, Yellow clownfish
  27. Amphiprion sebae, Sebae anemonefish
  28. Amphiprion thiellei, Thielle’s anemonefish
  29. Amphiprion tricinctus, Three band anemonefish
  30. Premnas biaculeatus, Maroon clownfish

Designer clowns

But us humans aren’t content with the natural beauty and variety of Clownfish, and we always want more. Clownfish were first bred in the early 70s as several factors including biological filtration, high prices of wild fish, dwindling wild stocks, poor quality of shipped specimens, marine food technology and commercial mariculture of food fish all gelled together. 

The USA was the first to breed clownfish and remain at the forefront to this day. Pioneers include Frank Hoff Jnr, Thomas A Frakes and Martin A Moe. Moe was first in 1974, and success in rearing larval clownfish coincided with success in culturing rotifers – clownfish food. Clownfish are now captive bred in their millions, and with captive breeding comes the opportunities to raise freaks, cross species, back-cross, and line breed to fix and enhance rare traits that pop up in two in a million fry. 

Black common clowns naturally occur in a limited range in the wild. Then you have the two species in the Percula complex – ocellaris and percula, and from that, there are now some 50 variants from completely orange “naked” clowns, to almost completely white Snowflake, Frostbite and Blizzard clowns, to almost completely black Domino clownfish, to longfin fish, and everything in between.

Picasso clowns are somewhere in the middle in terms of pattern extremity and price, and sort after. Prices rocket for the rarest morphs like Storm clownfish, which can fetch over £500 per pair, while at the other end of the scale, mass-produced common clowns from Israel are sold for around £20 each. You used to be able to tell the difference between a common and a percula clown, with percs having broader black margins to their white, vertical body bands, and at a scientific level it is down to fin ray counts, but I’d wager today’s designer clowns are very much a mixture of ocellaris, percula, and many regional variations, all many, many generations down the line. Most of the ocellaris and percula clowns now available have some sort of pattern mutation, and for every variation, there will be a breeder to christen it.

What is a mis-bar?

Mis-bars are something that crop up on many mass-produced, naturally vertically striped fish including clownfish and freshwater angelfish. Successive breeding can produce fry which have incomplete vertical bars on their bodies, often not stretching all the way down the body to the belly. A fish to be avoided at the wholesalers when this author was a livestock manager, but those mis-bars got shorter and shorter and now you can purchase clownfish with none of their characteristic vertical body stripes whatsoever – naked clownfish. But health is not affected.

Aquarium care

As well as being the most popular marine fish, Common clownfish are also the most recommended, and for lots of reasons. Number one is their ease of keeping. They don’t need an anemone (more about that in a minute,) they stay small, are hardy with regard to water parameters and are reef safe. This means that they can often be the first marine fish anyone ever keeps, be it in a small tank, a basic fish-only tank, or even a full-blown reef, and being mainly captive-bred, new marine keepers can find solace in the fact that they haven’t been taken from the reefs.

A pair of common clowns can be kept in an aquarium of 24”/60cm, or 60 litres upwards. Studies of wild fish reveal that small, young fish hardly ever stray from their anemone, with only adults of large species like Saddlebacks making forays more than a few feet. This is good for aquarium life, as it means that clowns don’t need as much space as larger, grazing species like surgeonfish, which naturally cover large areas to find food. 

Clownfish don’t need strong water flow, and they readily accept all kinds of food, from flakes and pellets to frozen brine shrimp. So you shouldn’t ever have a finicky feeder, like you would with a butterflyfish, and you shouldn’t have any trouble maintaining their weight like you would with a tang. Clownfish are safe with all mobile and sessile invertebrates like hermits, snails and shrimp, as well as all types of coral from soft, to lps, sps, and of course anemones, though don’t expect them to take to an Atlantic anemone, as they’re from the wrong part of the world. They’re safe with lots of other fish and are instant crowd-pleasers, especially when viewed by non-fishkeeping visitors to your tank. Their appeal is universal.

There are some rules that you’ll need to adhere to however when keeping clowns. Tank-bred clownfish jump out of tanks, especially when newly introduced, and especially at night. They’ll get out of the smallest gaps so you’ll need a really tight-fitting cover to keep them in. Imagine even one of a £500 pair of Black Storm clowns jumping out, but it happens all the time. 

Next is mixing clowns with clowns. Even in tanks of five feet or more, the safest bet is to have just one pair of clowns, of the same species. Add three individuals and the third will get bullied and die. Add four individuals and rarely you’ll have two happy pairs, one at each end, but usually, you’ll end up with two individuals. Add a pair of orange and a pair of black and you can almost bet you’ll get just one mixed pair of black and orange.

Mix common clowns with larger, more aggressive species like Maroon or Tomato, and the bigger, more aggressive pair will chase, harass and bully the more placid commons and percs, or even kill them. And when all this is happening your commons are prone to jumping again. There will always be exceptions, and I’ve kept and mixed many clownfish over the years, but none of them were truly long term. Often two clowns of the same type and batch don’t even get on, and “pairs” can be anything but. If you don’t like confrontation and quarrelling, just buy one.

The crowding conundrum

But Clownfish do live in numbers more than two in the wild, although it is always at the dominant female’s discretion. The female is the larger of the two fish, and there will only ever be one female per anemone. All clownfish are born male, and if a spare adolescent male arrives at the anemone he may be allowed to stay, but as exactly that, an adolescent, subdominant, non-sexual male. If the female dies or is predated, the dominant male will change to female and become the dominant female. 

One of the adolescent males will then become the dominant male, and male to female sex- change, but never from female back to male, is called Protandrous hermaphroditism. A healthy wild host anemone will have one female (the largest fish,) and all the rest will be male, descending in size and rank, all waiting their turn for a chance at the top job. 

This is hard to replicate in aquaria, although you can go the way of Malawi cichlids and stuff so many into a given space, that one can’t dominate. 

Bulk Reef Supply in the US created a Percula clownfish and bubble tip anemone only tank, and it was a success. Many public aquaria manage it too. BRS added 30 tank-bred black and white Snowflake clowns, and all from the same clutch. This it seems is key to managing aggression as they were the same size, same age, looked the same, and had all grown up in close proximity to each other. Remarkably, one of the 30 varied a tiny bit in pattern from the rest and was singled out and killed, so it’s not for the faint-hearted. 

When clownfish turn rogue

A wild clownfish has to potentially take on all comers, and in an aquarium situation that can also include you. Clownfish can chase and bite intruding hands from their owners, and even draw blood with those visible teeth. Clowns in anemones can show heightened aggression, as they have something to fight for and protect, and if they lay eggs like many pairs do, they want you, or tank companions, nowhere near them.

I recently had a pair of Tomato clowns. They lived in a five-foot reef tank and loved their red bubble tipped anemone. They would tolerate my hand and other tank mates within a few inches of them, until they grew, and started to spawn on a regular basis. They banished all other fish to just one half of the tank, would attack the algae magnet, would grab, chew and bite on catching nets and grunt, the end result being that I couldn’t clean any of their half of the tank, and if I placed a coral, they would pick it up and move it. They had to come out. 

Maroon clowns are aggressive too, but even commons and percs can bite, and attack and that includes each other. Remember they can change sex, but only one way, from male to female, and only once. So add a female fish to another female fish and it will end badly. From two males you should get a pair, but I see so many reef tanks with a clown in each corner, and one smallish reef tank owner I spoke with recently blamed their common clown for killing every newly introduced fish and shrimp in their tank, and eventually, its own partner. The rogue clown was removed, and everything was fine from then on. 

Environmental enrichment 

Clownfish naturally inhabit anemones in the wild. It is in their DNA, and they have evolved over millions of years to exist in a mutually beneficial relationship. I believe that if you have the skills and the budget to keep an anemone, and you can match the right species, you should do it. This does, however, mean that you will need to maintain reef tank water parameters, lighting and water flow, and everything that goes with it, including test kits for KH, calcium, magnesium, nitrate and phosphate. 

Anemones aren’t recommended for the new marine fish keeper, or even for new reefkeepers, but for those who have successfully maintained a reef for six months plus and know what a healthy coral looks like, and why and how their parameters should be maintained, then a pair of clownfish in an anemone, in your tank at home, is a beautiful thing. After all, that image is what most newbies got into the hobby for, in the first place. But there are many pitfalls to anemones, and many unsuitable specimens, and unsuitable species on sale. 

I heartily recommend the red bubble tipped anemone, Entacmaea quadricolor, as anyone’s first clownfish anemone, but only buy from a marine specialist who knows what they are doing, and better still can demonstrate successful clown and anemone symbiosis in their own display tanks. All clownfish can, of course, be kept without them, and they don’t actually need them in the home aquarium, but I think they look lost without them, especially in the modern reef aquarium with strong water flow, and anemone-less clowns are more likely to take up residence and annoy soft and lps corals without them, which does the corals no good. I also believe that a happy clownfish residing in an anemone is much less likely to jump out at night.

Picture by H. Krisp – Own work, CC BY 3.0,



Jeremy Gay

Author of three fishkeeping books and lifelong fishkeeper. Experience includes editor of Practical Fishkeeping magazine, editor of Pet Product Marketing magazine, multi award- winning livestock manager and aquatic store manager.