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OK, so i've been thinking. Always dangerous.

A majority of peeps that post over here are quite firm in their belief that goldfish need oodles of room and should not be kept in average sized tanks.


What I want to know is WHY.


More specifically, I want to know why it is that a 4cm fantail in a 20 gallon is a problem.


Now, I hate to admit it, I desperately want a goldfish, but all this talk of 55 and up has scared me off. I am positive that i could keep a goldy happy in a 20 for a decent period of time, but I am afraid of being spoken down to or being yelled at for even attempting such a thing.


So, my thoughts went something like this:

What is the average growth rate for a standard fantail of approx 4cm if not stunting has occurred? approx x mm per z? (assuming optimum tank and water conditions)

How much ammonia does a standard fantail of approx 4cm produce? how is this measured? per square inch of skin? (not interested in cycling or other fish, just from a pure production pov)

How does the above differ from say, an oscar or a pleco? Or a neon tetra?

What damage does stunting cause OR more importantly, assuming perfect water quality (play along, perfect hypotheticals ), how much is dependant on the physical size of the enclosure?



I am not trying to get people to agree with me or give me permission to keep a goldie, I just want some information based more on measurable fact than anecdotal evididence. As much as I understand how important anecdotal evidence is, I need something more concrete.


And yeah, I'll admit it, I was going to buy a goldie and just not tell anyone.

Last edited by Callatya at 15-Nov-2005 20:23

For animals, the entire universe has been neatly divided into things to (a) mate with, (b) eat, (c) run away from, and (d) rocks. - Terry Pratchett

I do a weekly change. When I have tested for ammonia have been in the clear. I do not over feed. At least one day per week without food (them not me). wish-ga has been happy and thriving for over 5 years (the fish not me). The tank is not a 55 gallon.

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~~~ My fish blow kisses at me all day long ~~~

The first I'd heard of a 55 gall minimum was on this forum so I put it to another forum I went on and they suggested it was a little excessive. Goldfish grow to all different sizes if you go to http://www.thegoldfishbowl.co.uk/ and go to atlas of species, then coldwater, it gives you the max sizes of all the types of goldfish.
My goldfish tank is approx 40 (UK) galls and has 3 fanices in there. They get along fine and are breeding like rabbits the eldest is about 7 years old, the other 2 are about 2 years old. I've never had any problems with any diseases or anything like that.
I think for comets and shubs they need a lot more room cos they are so active, they are better suited to ponds really.
I would say to start 20 UK gallons for the first fish (purely because a 10 gall tank does not have enough swimming space) and then another 10 UK galls for each extra fish depending on the fish. If anyone gets confused, 10 UK galls is roughly 12 US galls.

What are the dimensions of your 20 gall tank? As long as there is plenty of swimming room it should be ok but if your fish gets big you might want to upgrade.

Last edited by Fishy-Fishy at 16-Nov-2005 06:53

Its a 24x12x16", and I also have a 24x12x20" which is just that little bit taller.


i've come across some odd minimum tank sizes around the place, but FP definately has the highest.

I do remember it being 20USG minimum + 10 for each additional, and ONLY fancies, but somehow that morphed to 55USG or a whopping great pond.

I understand that for body shapes like shubunkins or comets, if nothing else they need swimming room, but fancies are very hindered in that department, and unless they excrete masses of ammonia, I cannot see a logical reason why a young fish cannot spend a few years in a standard sized tank.

you know, if i can slip it past the BF, i just might do this....




For animals, the entire universe has been neatly divided into things to (a) mate with, (b) eat, (c) run away from, and (d) rocks. - Terry Pratchett

I think 55 gals.+ for a goldfish is pretty excessive, myself, but I do understand the need for fish like that to have a lot of surface area, and a whole lot of filtration. I think one young fantail in a 20 gallon (preferably a long or breeder sized tank) with filtration rated for 30-40 gal. tanks would be okay for several years. You just have to keep up with the tank maitenance, water changes and gravel vacs as well as regularly changing filter media, and keep an eye on water quality. It's true that these fish can get absolutely huge, and it can happen fairly quickly, so if you do want more than one, you should definitely plan to upgrade to the 55+ gal. tank in their future.

Hoping that there must be a word for everything I mean...

OK, well, I have to say I'm rather heartened that I haven't been charged with crimes against cassius yet I am undecided if i should devote the tankspace or if i should go with a similarly sized pond (which could be designed to provide more swimming space I suppose) but having a discussion about it in this way is quite interesting

I understand they are relatively fast growers, and have the option of a few ponds and pond fish shops for the future. Definately would not consider keeping a fish with this growth potential in a 26 for any extended period of time.

Would they have a 3-5 month period where the temperature drops that they would not grow as quickly (remembering that it doesn't snow here and minimums are about 12*C during the day and 2*C at night)?


Regarding my original queries, does this information exist somewhere? does anyone have it in a book or something?

For animals, the entire universe has been neatly divided into things to (a) mate with, (b) eat, (c) run away from, and (d) rocks. - Terry Pratchett

The only thing to be very careful of is stunting, fanices are e to swimbladder problems anyway but if they are stunted it gives them a much higher chance of getting a swimbladder problem.

dont forget it is different with someone like u, b/c u know about it, it is just fustratiting to tell people that have no intent of moving the goldfish for ever.

since they are kinda though fish, weekly water changes, i think the avg size growth varies, on conditions. and correct me if i am wrong, but when the fish looks to be maxxed out in size, in a small tank then i think that is when u know it is stunted, right?

heck, i have small koi inside the house in small tanks, for the winter, but they are being shipped out as soon as possible.

Last edited by bettachris at 16-Nov-2005 18:30

Nice post bettachris * <--- that's a gold star to pin to your lapel

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~~~ My fish blow kisses at me all day long ~~~

What is the average growth rate for a standard fantail of approx 4cm if not stunting has occurred? approx x mm per z? (assuming optimum tank and water conditions)

Growth rate is highly variable. It depends on a lot of things, water quality, temperature (higher temps = faster growth), food, space available, population density, social interaction (yes, even social interaction) etc. I know you were looking for a less anecdotal answer but in this case it's really hard to give one just because there are so many factors that play into it. Having kept lots of goldfish, don't underestimate their potential to grow really quickly, especially goldfish in a warmer water aquarium. Having kept fantails, in optimum conditions growth of a few inches a year in young fish (or even more) isn't uncommon. I doubt you would see much change in growth rate or much real long term damage keeping them in a 20 gallon tank instead of say, a 55 gallon for a few months to a year, I can't honestly say beyond that because I haven't kept them in a confined area like that for any extended length of time (after the obligatory bowl experience when I was 5, RIP goldy).

Growth rate is also very fast when they're young and slows down as they age. They tend to do a lot of rapid growing in the first few years, then keep growing but not nearly as quickly as they did before. A 4 cm goldfish in a healthy environment is not going to stay 4 cm for long. I would not be surprised to see a small fantail double in size in a few months.

How much ammonia does a standard fantail of approx 4cm produce? how is this measured? per square inch of skin? (not interested in cycling or other fish, just from a pure production pov)

Again it's really hard to give any real answer to this because it's so highly variable. Some of the same factors come into play, temperature, feeding, etc. To be honest, I think people spend way too much time worrying about nitrogenous waste in fish tanks and not enough time looking at other pollutants.

First of all, unless you're new to aquaria or something, you shouldn't ever see ammonia in the tank. Nitrite itself hardly ever reaches a really toxic level unless you're doing something seriously wrong, so it's not too much concern either. Inorganic nitrate (eg. KNO3) can and has been dosed to ridiculous levels (Tom Barr says he's dosed it to 120 ppm for 3 days without losing any otos, and otos are *supposed* to be exceptionally nitrate sensitive) without many fish losses, but any experienced fishkeeper could probably tell you they've lost fish or know of someone who has, presumably due to water quality issues at far lower test readings for NO3.

Anyway the point of all that is that personally, I don't buy the idea that NO3 is all that bad in itself and if you have any experience in keeping fish, it's the only nitrogenous waste product you'll ever see. I think there would have to be other chemical pollutants at work in a tank that make fish sick when they start building up. Instead, high nitrate readings (in my mind) serve as more of a general indicator that the tank water is becoming polluted and needs a change. Anyway, people tend to get tunnel vision with nitrogenous waste, and I don't think it makes much sense in dealing with a complex biological system.

With goldfish, if you've ever kept them it's obvious they're messy. A fully grown fantail can have close to the same body mass as a fully grown comet because they're bred to be so stocky. They eat a lot, they make a mess with their food, poop a lot, mess up the substrate, they're just messy fish in general. Because nitrogenous waste can be taken care of so easily (water changes, proper cycling, etc.) I don't consider it to be the main limiting factor in deciding tank size. In a smaller tank you will obviously need to do a lot more maintenance to keep the tank clean and healthy for them, large frequent water changes and good filtration are important in large tanks but even more important in smaller ones.

Fancy goldfish will naturally produce a lot more waste/ammonia than fish of a similar length because they've been bred to be so compact. I would say a fully grown comet and a fully grown fancy would produce close to the same amount of waste because they have close to the same mass, it's just distributed differently.

How does the above differ from say, an oscar or a pleco? Or a neon tetra?

Goldfish are by far the messiest. Again, I don't have scientific data on this but having kept them, large plecs, neon tetras, and with a lot of experience helping other hobbyists that keep large cichlids, I can tell you goldfish are a lot worse. For ammonia alone, they seem to produce a lot more than other fih of similar mass, like large plecs or cichlids. Just as a guess from the amount of upkeep they require, I would say a 4 cm fancy goldfish would produce the equivalent waste of a ~10 cm pleco or cichlid. They're very very messy. Plecos poop a lot but don't dig in the substrate much and don't get little bits of food everywhere, they scavenge around the tank for uneaten food and tend to be fairly low maintenance. You'd need a whole lot of neons to come even close to that amount of ammonia, and you'd never see the same amount of solid waste, food bits lying around or anything that you do with goldfish, I don't think it's really possible to compare them.

So sure, the waste of a 4 cm goldfish should be easily manageable, but the fish isn't going to stay that small for very long.

What damage does stunting cause OR more importantly, assuming perfect water quality (play along, perfect hypotheticals ), how much is dependant on the physical size of the enclosure?

This is the fun bit really. There are a LOT of stunting myths, so hopefully a bit of discussion might get some more info out there.

I have yet to see any evidence that stunting will cause fishes internal organs to keep growing and eventually explode. If anyone has any real evidence of this, let me know, but I don't personally think this myth makes any sense. There are similar myths, most of them based more on scare tactics and misinformation than any scientific basis that I've ever seen.

Stunting or slowed growth IS, on the other hand, a complex physiological adaptation to stress. There are a lot of different causes for stunting, none of them beneficial to the health of the fish. The actual physiological effects of stunted growth on a fish are largely dependant on the factors causing the stress response. So, fish stunt for a variety of reasons because it's a symptom of a greater problem, the underlying cause of stress will determine the effect it has on the fish.

Poor nutrition, parasitism, water pollution including growth inhibiting hormones, psychological reasons (sounds like quackery but psychological stress can stunt fish), stocking density, enclosure space, social interaction, and generally poor health will all cause a fish to show slowed or even halted growth. As an adaptive response to poor environmental conditions, fish concentrate energy and resources on adaptation to stress and survival rather than growth. Stress causes stunting, so stress is the real problem. So instead of examining the effects of stunting itself, I think it's much better to take a more holistic approach and consider the effects of stress on fish health.

I know I tend to really beat people over the head with the stress idea but understanding stress, its causes and effects, is really the key to keeping healthy fish. Disease, stunting, failure to thrive, premature mortality, all are symptoms of stress.

Overcrowding, which can include keeping fish in tanks that are too small, leads to a variety of problems because it's extremely stressful. If water quality is perfect (never is in an overcrowded tank, but OK), you will still see other negative symptoms with stunting:

- reproductive abnormalities, stunted fish are commonly sterile, may never reach sexual maturity and/or produce viable young
- skeletal deformity
- abnormal behaviour, may be psychological effects (yes, I know fish psychology sounds like quack science, but they do have brains, animal psychology is interesting stuff )
- failure to thrive
- illness (parasitism is extremely common)
- wounds that don't heal, capacity to heal is often diminished in stunted fish
- general ill health
- premature mortality
- swimbladder issues, especially in goldfish
- any other symptom of chronic stress you can think of

Symptoms of overcrowding are accumulative because of its chronic nature, fish are very good at adapting to acute stressors but adaptive mechanisms tend to break down as the fish is continuously exposed to stressful stimuli. Stressful stimuli force the fish to allocate resources to adaptation before everything else, so really every physiological process suffers for it. The related problems compound over time.

Bottom line: a tank/enclosure that's too small stresses the fish out. Stress is bad and will make your fish sick and eventually kill them. Slowed or stunted growth is a symtom of chronic stress and definite cause for concern.

There is some evidence that fish release hormones that inhibit growth, most notably somatostatin which may be released into the water via the gut and cause a greater decrease in growth. However, stunting seems to be primarily internally regulated as an adaptive response to stress in order to promote survival.

Just reading through some of the other responses because I get the feeling I won't be well liked for this one....

I don't think it's reasonable to expect to keep a goldfish in a tank smaller than ~55 gallons for any extended length of time. You can start out with a smaller tank, but be prepared to upgrade to a much larger one in as little as 6-12 months. I usually advise people to keep the long term needs of the fish in mind when they're buying them. If you can't provide a larger enclosure when it's needed or are unsure you'll be able to do it, don't keep them.

Goldfish are very social fish and really like company. It's much better to keep them in groups, and given their large size you're automatically limited to a fairly large tank if you want to keep more than one.

A lot of posters said they have goldfish that are a few/several years old in smallish tanks. I tend to be a bit extreme in minimum enclosure sizes but there's a lot of experience and research behind those beliefs. Lack of space stresses fish out and leads to ill health, limiting stress means healthy fish. If that means keeping them in big tanks or not keeping them at all, the decision isn't a difficult one for me and that's the opinion I'll share with others.

Would they have a 3-5 month period where the temperature drops that they would not grow as quickly (remembering that it doesn't snow here and minimums are about 12*C during the day and 2*C at night)?

Actually fancies don't do all that well with lower temperatures, so I wouldn't keep them outdoors for the winter there. Usually indoors without a heater is good. In colder temperatures they get stressed out and diseased easily.

nd correct me if i am wrong, but when the fish looks to be maxxed out in size, in a small tank then i think that is when u know it is stunted, right?

Yep, you'll see stunting as it happens, growth slows down. One problem with this is that a lot of people don't know the optimal growth rate for goldfish or don't really know their potential size, so can't recognize an abnormal growth rate when they see it. It's important to move them out before any stunting happens though, because stunting is often not the first visible sign of stress. It takes some experience to recognize early signs of stress, so that's another reason why I wouldn't generally recommend an inexperienced fishkeeper house goldfish in small tanks, even temporarily. Stress would be the indicator that it's time to move them, not just growth.

Sorry for the novel.

And I forgot to post my links.

http://www-heb.pac.dfo-mpo.gc.ca/congress/2002/Growth/Growth.pdf - Heavy read but a TON of info about growth in that one

http://www.skepticalaquarist.com/docs/fishes/physfish.shtml

http://badmanstropicalfish.com/stories/chat/chat_3-12-04.html

(I had more but I accidentally closed a browser window and lost em)

Some of it is my own knowledge from uni courses, work with the local conservation authority, discussions with my vet, hobby experience, etc.


Last edited by trystianity™ at 18-Nov-2005 11:36