Stocking for goldfish (i.e. the number of gallons needed for each goldfish) is controversial, to put it mildly. But it all can be summarized in one bullet:
It all boils down to an OPINION
It is the OPINION of many hobbyists that goldfish need very large aquariums in order to “thrive”. It is my OPINION that goldfish do not need large aquariums in order to “thrive”.
To illustrate the stocking of common goldfish just look at this tank:
There are at least a dozen very large (five to six inch body length?) fully grown goldfish thriving in what appears to be about a 75 gallon tank. These fish are obviously not the victims of “animal cruelty”, at least not in my OPINION.
Stocking Narrow Bodied Goldfish
Because of the inadvertent selective breeding of the Chinese the “narrow bodied” goldfish can live in much more crowded conditions that a normal fish. They “grow to the size of the container”. They can also withstand poor aeration and poor water conditions much better than any other fish. So the stocking for the “narrow bodied” goldfish is the same as for a five inch fish.
In my OPINION this stocking is:
Now these numbers will send the many hobbyists absolutely bonkers. So be it. It is very frustrating to see on social media where newcomers to the hobby who start out with common goldfish in small aquariums are shamed and degraded as being inhumane and guilty of animal cruelty. This “shaming” is wrong. These people’s aquariums and goldfish will probably do just fine.
Below is a photo of a goldfish that had been kept in a one gallon tank for three years. It was fine and obviously thriving. The water is clean and well filtered. The fishkeeper obviously kept very good care of the goldfish and the fish is healthy and not “deformed” in any way. It has been dwarfed by natural hormones, a process which is completely harmless.
Also note that I’ve seen some very good “nano aquariums” as low as one gallons with goldfish swimming and thriving in them. There is NOTHING WRONG with that. It is not “cruel”, in my OPINION. The charts above are just OPINIONS and can be violated with abandon, especially with narrow bodied goldfish. Just try to get some filtration and some aeration in the small tanks. It will help keep the fish healthy.
This is a photo of two goldfish which have been in a small UNFILTERED aquarium for 21 and 23 years:
These goldfish are obviously healthy. They have been made small by hormones produced in response to the small aquarium but they show no evidence of compressed organs. They have most certainly been “thriving”, at least in my OPINION.
Note that these numbers in the table above are for adults. Small babies which are only two inches long can obviously be kept in much more crowded conditions. They would need to transition to the stocking above as they reach adulthood.
Here is a FOUR gallon aquarium with ELEVEN goldfish that were thriving (again, in my OPINION!):
Stocking Fancy Goldfish
Fancy “wide bodied” goldfish need better water quality and a larger filtration system compared to a common “narrow bodied” goldfish. Hang-on-back filters or air operated sponge filters are not recommended for fancy goldfish as they don’t supply the necessary bacterial water cleansing that fancy goldfish need.
These fish are very wide bodied and need to be stocked as six inch fish even though they rarely exceed a body length of five inches. In my OPINION, these are the stocking requirements for genetically dwarfed goldfish:
Note this sizing chart is a complete reversal of what you will find the “experts” recommend. “Experts” recommend that narrow bodied goldfish have larger aquariums than genetically dwarfed (“fancy” or “wide bodied”) goldfish. That is incorrect because of the genetics of the two fish.
With very good filtration with huge amounts of very good media which has been in place uncleaned for four months or more, one can stock at the heavy levels shown above. Let us be very clear, we only “recommend” these heavy stocking levels ONLY FOR WELL FILTERED AQUARIUMS WHICH HAVE LARGE FILTERS WITH GOOD MEDIA THAT HASN’T BEEN FREQUENTLY CLEANED!!!!! Heavy stocking requires ten times more filtration than light stocking and three times more filtration than moderate stocking.
But also note these are “recommendations”, i.e. my OPINION, nothing more. If you want to put a fancy goldfish in a two gallon aquarium, just do it. If the fish has excellent aeration and superb filtration there is probably only a small drop in life expectancy in the small tank. There is nothing “cruel” about it in my OPINION.
Now there is a caveat about heavy stocking. Each goldfish needs an amount of biofiltration to be healthy. Heavy stocking means there is a need for much more biofiltration, ten times the biofiltration of light stocking. Internal filters (the small cartridge filters which fit inside the aquarium and which come with most store bought kits), cartridge hang-on-back filters, and air operated sponge filters have very small amounts of biofiltration and should be avoided with heavy stocking.
Let us be very clear, we only “RECOMMEND” these heavy stocking levels only for well filtered aquariums which have large filters with good media where the media isn’t cleaned except when it plugs up. Heavy stocking IDEALLY should have three times more filtration than moderate stocking and ten times more filtration than light stocking.
Let us also be very clear that these “recommendations” are just OPINIONS, nothing more. As we pointed out above one of the longest living goldfish in the world was in a small tank with NO filtration and NO aeration and was thriving. When it comes to goldfish I like the Nike phrase “just do it”.
Note also that filtration needs are dependent on feeding. If it is a newbie to the hobby feeding his fish three or four times a day all they can eat the filtration needs are much higher. If it is an experienced hobbyist feeding only 1% or 2% of the body weight per day in carefully measure doses, then the filtration needs will be much less.
Long finned varieties such as the comet and sarasa need more biofiltration than short finned goldfish. So a heavily stocked aquarium with long finned comet or sarasa goldfish will need more attention to biofiltration.
Fish Police Replies
Whenever I post the ideas above on social media I will get a bunch of negative comments. The following it typical:
“I’d be super interested to read what your(Sic) reading! Because the Florida University of Aquatics has peer reviewed studies that state quite the opposite! I’m not bashing, but I’m a woman of science so if you’ve got articles or studies on these goldfish I truly would love to give it a read”
Now this thread continued on for awhile. I ask this individual for the “peer reviewed studies” she was referencing, with a note that the University of Florida Tropical Aquaculture Laboratory (the only Aquaculture Research Operation associated with a Florida University) had no such studies.
She came back with a reply with a laughing emoji about me asking her for the studies. Her reply referenced NO studies (believe me there are none, not by ANY University!) and a sentence: “This isn’t the University of Florida but instead is the Florida University of Aquatics“. “Aquatics” is the science of human swimming. If you Google “Florida University of Aquatics” you get a bunch of articles on how to swim and swimming pools. So much for the “woman of science”. The Fish Police folks just never quit!
Further Articles on Goldfish
For those wanting to delve deeper into keeping goldfish one can go to the following links:
Aquarium Science Website
The chapters shown below or on the right side in maroon lead to close to 400 articles on all aspects of keeping a freshwater aquarium. These articles have NO links to profit making sites and are thus unbiased in their recommendations, unlike all the for-profit sites you will find with Google. Bookmark and browse!