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Are Small Fish Tanks Cruel? Everything You Need to Know!

Lindsey Stanton Profile Picture

By Lindsey Stanton

muliple sized fish tanks

I’m probably not going to change your mind if you have a strong opinion on tank size. People usually just do what they want to do at the end of the day.

But I’m putting it here for those who care to read the rant. When people realize that goldfish CAN live in small tanks, there’s a common argument that follows.

I cannot even BEGIN to tell you how many times I’ve heard this: “Surviving doesn’t mean a fish will live a happy life. You can live in a closet, but it doesn’t mean you’d want to!”

There are two points I’d like to say in reply:

1. How many gallons equals a closet?

girl watching goldfish in jar
Image Credit: Yuli4kaSergeevna, Shutterstock

Fish aren’t people. They understand space in a totally different way (after all, need I point out they swim everywhere they go?). Comparatively, ALL indoor tanks are small tanks when you realize the “ideal” is a pond. Does that mean you should only keep goldfish in a pond?

Absolutely not! Whether it’s 5 gallons or 55, both are a drop in the bucket when you think about a pond containing thousands of gallons.

But fish have been kept indoors as pets just fine for thousands of years, and it’s the same with cats and dogs. Maybe they have considerably different conditions than in the wild, but they can still thrive!  Speaking of thriving…

2. Define an unhappy fish

sick goldfish laying on bottom of aquarium
Image Credit: mrk3PHOTO, Shutterstock

Is it one that’s spawning? Certainly not. Anyone who has tried to  breed goldfish knows this one thing: goldfish will only spawn when they are very happy, and the conditions are just right.

Please tell me why my “miserable” 2 fantails spawned every 5 days in their 3-gallon bowl. The bottom line? A fat, perky, hungry, energetic, exploring fish is not miserable. Especially not a spawning one!

I’ve seen several miserable goldfish over the years, and many of them were in big tanks.A truly miserable goldfish will show it by one or more of the following:

Signs of Unhealthy Goldfish
  • Lethargy
  • Reduced appetite
  • Losing weight
  • Bottom sitting
  • Unable to swim properly
  • etc.

As with people or other pets, there are physical signs that you can see when a fish is not thriving. But I have yet to see a correlation between small tanks and fish misery. If the fish is acting like this in a small tank, it’s because it’s diseased, aged, or suffering from improper water parameters.

Again, they can do these things in a big tank. Big tanks are not the “cure-all” for water quality problems, that’s for sure. I keep both big tanks and small ones. That’s why I never jump to the conclusion that the aquarium itself is the problem and the reason the fish is unhappy.

Blaming the tank is exactly what people do when they don’t know what’s wrong. The problem is what’s going in INSIDE the tank.

divider fish plants 2

Can Small Tanks Ever Be Cruel?

goldfish bowl
Image Credit: LUIS PADILLA-Fotografia, Shutterstock

To be fair, yes, I think there can be such a thing as “too small of a tank.” However, I’m not quick to put a number on it. Some people say, “any tank under x number of gallons for x number of fish is too small.”

But there’s really no scientific support for such a statement. Science has yet to give us an exact number to support any rule for the tank size. How do you tell if a tank is too small? I go by two things:

1. Not enough swimming space to prevent muscle atrophy

Obviously, if the fish can’t turn around and move properly, this can harm its well-being. There’s no formula for x number of gallons that prevents muscle atrophy per inch of fish. Science is quiet on the topic.

The Japanese have used the ratio of 3–4x the body length of the fish for the diameter of the vessel when grooming the Tosakin. I personally like this “rule” as the Japanese were masters at keeping and breeding goldfish.

With all of their experience? They would probably have a pretty good idea. Muscle atrophy is proven to have negative effects on fish and is usually preventable through nutrition and by making sure they can comfortably swim around.

2. Too many fish to be supported by the available space for filtration or plants

Sometimes there just is not enough surface area for the plants to grow properly or even to add a filter. This can lead to problems like oxygen deprivation and water quality issues. Again, sorry if you want a number here. I don’t have one.

Nobody else does either, that’s supported by any studies (as far as I have been able to find). I think it’s actually not a common scenario. You might have to do something totally unreasonable like put 10 one-inch-long common goldfish in a 1/2 gallon bowl to have this issue.

Most people have more common sense than to do that. Finding the right balance of fish to plant to filter space might take a little practice. It can be done in a small tank as well as a big one, but sometimes you just have to get a little creative. However, it can be done, even in a small tank or bowl.

There’s no one-way-works-for-everybody rule. I still personally recommend most people don’t keep just one goldfish all by itself, but some people do, and it has worked fine for them for years.

Are Small Aquariums Harder to Maintain?

dirty water
Image Credit: Chaikom, Shutterstock

The short answer is they can be, but they don’t have to be. The answer totally depends on your setup. I can say from experience that doing a 50% water change on a 5-gallon tank is much easier than on a 30-gallon.

Some may argue the toxins build up faster in the small ones. Personally, I have found with goldfish that big (uncycled) tanks can become toxic in a surprisingly short amount of time, even with low stocking and light feeding.

At the end of the day, a bigger tank is not the solution for water that is always dirty, smelly, or uncycled. These are challenges that need to be addressed by filtration.

Dilution will only get you so far for so long before you start going crazy again and your fish are sick from bad water. I’ve had big tanks that are triple the work of small ones with the same species of fish (goldfish). It really comes down to other factors in your aquarium besides the size of the enclosure itself.

Join Nano Goldfish Keepers

If you’re like me and you’re sick of the shaming and guilt-tripping over small tanks, good news: I made a group for people who keep small aquariums – or “overstocked” ones (according to some “rules”). It’s called Nano Goldfish Keepers.

Any size tank or fish is welcome, and it’s a judgment-free zone. Feel free to join if you want!


People have strong opinions on both sides of this topic. But since there aren’t any clear studies to show what’s right or wrong, all we can do is try different things and see what happens. Some people firmly believe that keeping goldfish in small tanks is mean to the fish, and they don’t want to consider other ideas, even if others have had different experiences.

I used to be on that side of the fence myself. But the more I learn, the more I realize how much there still is to learn. And sometimes, what seems like a disaster waiting to happen to one person is a breeze to somebody else who actually tries it.

Read More: 5 Basics of Nano Goldfish Keeping

Featured Image Credit: MOUii, Shutterstock

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