I have a lone goldfish, a comet, about 10 cm long from tip to tail. I want to buy a second fish and am wondering about size.

Is it ok to introduce a much smaller goldfish, or maybe three smaller goldfish; so they are a little protected group and not an odd number,I don't want any of them to be left out. Or is it preferable to get a fish a similar size to my existing fish?

I am looking for some expert advice.

Without concern for pond size, what are the general guidelines for matching fish like this for size?

Is there a danger a smaller goldfish could be eaten by the larger goldfish?


I am wanting to know about matching goldfish (in this case comets), as opposed to what will or will not fit in my pond. The dimensions of my pots were brought up in the comments, but it is not answering my question about the compatibility of the fish with regard to size (in this case, comets).

edit 2

I have been investigating fish ponds for the past 4 years. In the meantime, my neighbors gave me their goldfish. I am wanting to learn about the fish, prior to buying a large fish pond.

  • I am preparing my third pond and am not sure how to house them.. I have three fish..
    – user6796
    Nov 5, 2013 at 16:18
  • 1
    A good rule of thumb, for volume, is about 20 gallons (75 liters) for initial fish and another 10 gallons per fish after.
    – Joanne C
    Nov 5, 2013 at 16:23
  • @John, regardless of the size of the fish? (I remember hearing a rule of thumb that was cast in "inches of fish per gallon", which is why I ask.) Nov 5, 2013 at 16:36
  • @Skippy-psI'mawoman seems that you have more or less 70 liters in that pot pond, so just one fish would be recommended... Nov 5, 2013 at 16:37
  • @woliveirajr yes, I worry about him being lonely :(
    – user6796
    Nov 5, 2013 at 16:37

3 Answers 3


So, I'd like to address a couple of challenges first and then make a suggestion that might work.

Size of Tank

The ponds you currently have are basically sized for a single goldfish. The risk factor here is that more than one goldfish will overload the environment as their waste product can be toxic to them.

Goldfish are very hardy and can survive in less than ideal conditions, but it's not necessarily true that they're thriving. Bear in mind that a healthy goldfish should reach to about 24cm by their second year. Look for black spots or abnormalities on the fish to detect the effects of their waste product on them.

Now, the RSPCA of Australia lists that 50 litres is a minimum tank size. So, there is a little bit of dispute about the minimum and if the fish is healthy, you may have some room to spare.

Also, as you grow the size of the environment, the rule of thumbs are best to keep in mind. Ideally 20-30 gallons to start, add 10-15 for each new one. Err to the side of more, it will never hurt to have more space.


Goldfish are omnivores that eat plants and other aquatic animals and they're opportunistic feeders. They will, of course, eat other fish as consequence, especially if the fish can fit in its mouth. So, obviously, any companion fish for them needs to be bigger than what the golden fellow can directly eat otherwise they may dine on your intended companion fish, including other goldfish.


Getting additional goldfish may result in having more than you expect... Unless you've correctly sexed the fish. Something to keep in mind. Mind you, domestic goldfish will often eat their own eggs, so you may not end up with a litter as it were anyways.

Immediate Considerations

So, goldfish are social creatures and that does argue for your concern about companionship. I don't think your tank sizes are ideal for having an additional goldfish, I think you're pushing the edge of good size for a single. The link I just gave makes some recommendations on alternate companion fish. Of those, I would actually recommend going with the danio (or zebrafish) as being the most suitable for your conditions.

The danio are hardy fish and social fish that get along well with other species. They're active and playful, as are comets, so would seem to be a good blend. They're easy to keep and feed being omnivores. Tank size recommendations are about 5 gallons per fish, so you might be able to get a couple in there. I would probably start with one and see how it gets on before adding any additional ones.

I realize that I've pushed on the tank size a bit and I have because hardy fish species can create an illusion of thriving when they really aren't. While I agree that your goldfish need companions, I think you might want to pay extra attention and care to their health and activity if you introduce additional fish to their current ponds.

Future Considerations

So, adding the danio today isn't a bad idea and may alleviate the initial concerns about the the current fish. With respect to having more goldfish together, given a future environment, the considerations are:

  1. Size. Larger fish won't normally be an issue if there is sufficient space, but if a larger fish is much larger and more aggressive, it may be best to move them out (last paragraph) or separate from the smaller fish regardless of space.

  2. Type. Mixing varieties, especially common with fancy, can lead to problems. The comet variety, as I noted earlier, is an active fish and so you probably want to keep like to like.

I would generally try to size the new fish to be reasonably close to the size of the current ones where possible. This is not an absolute must, but will enhance the chance of the introduction being successful. Bear in mind that you can still keep the danio if you do end up adding them to your current ponds.


As @John Cavan comments (and this site too), goldfish in general need:

Fancy goldfish: 3 feet long and a volume of at least 20 gallons for one goldfish. If you plan to keep more than one goldfish in your tank then add an extra 10 gallons for each additional fish.

So, your pot pond has more or less 70 liters (18.5 gallons). Your pond has room for one goldfish, adding another one will more likely make them fight than become friends.

Adding smaller goldfish might not be the solution either, since they will grown and there'll not be room for them in the future:

When properly cared for, goldfish will not stop growing.

source: this site: Goldfish myths debunked

And will it be lonely?

Note that a goldfish will live happilly alone as well, so if your tank can't handle a second fish because of size constraints, it is better to keep just one in a healthy

source: http://www.csh.rit.edu/~tonyl/goldfish/testarea/advcare.htm

  • You didn't actually address the size of fish choice as a companion... which is why I didn't want to focus on pond size I still gave +1
    – user6796
    Nov 5, 2013 at 22:57

I had a cory catfish with a goldfish for about 5 years. They were happy together. The goldfish died and now the cory is in a larger aquarium with many fish & is still living & happy.

  • thnx Jeni, I'll bear this in mind. How big were they when you put them together?
    – user6796
    Nov 11, 2013 at 1:38
  • The goldfish was about half the size he/she became and the cory was the same.
    – Jeni
    Nov 15, 2013 at 20:04

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