Can You Put Small Goldfish with Big Old Goldfish?


Goldfish are not known to be aggressive or violent. So why is it that they can’t be tankmates to smaller Goldfish or other freshwater fish? Let’s find out as we talk about Goldfish compatibility, size differences, and tankmates.

Can Different-Sized Goldfish Live Together?

There are hundreds of species of Goldfish, but you have to find the right combination that would work together.

It’s possible to take care of differently sized Goldfish as long as the species are compatible and the size difference isn’t too great. The smaller fish shouldn’t be too small that they may be mistaken for food. The aquarium should also have enough space.

Some examples of compatible species are Comets, Wakins, and Shubunkins. Another good combination is Fancy Goldfish with other Fancy Goldfish (example: Ryukins, Fantails, Black Moors, and Lionheads).

These are good combinations because they have similar:

  • water requirements including temperature
  • speed
  • personalities and energy

Delicate species like Celestials and Bubble Eyes should only be kept with their own species.

To keep a particular combination together, always make sure you have a big enough tank. A small tank causes overcrowding, making the bigger Goldfish bully the smaller ones. Overcrowding leads to fights over food and territory.

Will A Big Goldfish Eat A Little Goldfish?

Now that you got the right combinations, you have to get the right size of the smaller Goldfish for it to work.

A bigger Goldfish will generally not harm smaller fish including juvenile Goldfish or those of smaller breeds. However, they can be opportunistic (similar to many other fish) and may eat whatever they can fit in their mouths, including Goldfish eggs and hatchlings.

Can You Put Small Goldfish with Big Old Goldfish?
Can You Put Small Goldfish with Big Old Goldfish?

There are ways to prevent a Goldfish from eating another Goldfish. Check out our tips:

Tip #1: Separate mom from eggs

Goldfish may be known to be smart, sociable, and have long memories. However, they lack parental instinct. Thus, they see little eggs and babies as food.

If you’re familiar with how a Goldfish lays eggs, you might want to put the would-be momma Goldfish in a breeder tank. Wait until she lays all her eggs and then put her back in the main tank right after.

Alternatively, you can put a mesh screen or divider to separate the eggs from the rest of the fish. You can do this if you have a big enough tank, say, a 125-gallon. Remove the mesh once the hatchlings become juveniles and no longer in peril of being eaten.

You can also scoop the eggs or hatchlings out of the tank to save as much as you can. Move them to a growout tank to stay until they’re big enough (about an inch or so) for the main tank.

Tip #2: Don’t keep Common or single-tailed Goldfish with Fancy Goldfish

Do you know the difference between the two main types of Goldfish? Common Goldfish are those that have slender bodies, single tails, and generally bigger sizes. They grow up to an average of 12 inches long. On the other hand, Fancy Goldfish are rounder, smaller (6 to 8 inches on average), and have double tails. Because of their features, Fancy Goldfish are also slower.

This makes for an incompatible combination if kept together in a single tank. The faster fish would eat up all the food and the slower ones will starve. The Fancy Goldfish’s tails are also a constant temptation to nip for the bigger Commons. Because single-tail Goldfish are more boisterous, they could stress out the more docile Goldfish tank mates.

Aside from speed and length, another main difference between these two types is that single-tailed Goldfish and those like it are stronger swimmers than Fancy Goldfish. Therefore, water flow rate requirements in the tank differ between the two.

The temperature difference is not so much a hindrance to keeping these two types together, but it can still be if you introduce one type and the other falls sick. Common Goldfish generally like colder temperatures of 65 to 70°F, while Fancy Goldfish love more tropical climates of 68 to 74°F.

Tip #3: Remove dead fish ASAP

Along the same lines of opportunism, Goldfish might also peck on a dead Goldfish (not an often occurrence but it does happen!). So when a fish dies in the tank, remove it right away. This also helps you prevent an ammonia spike due to the rotting carcass.

Tip #4: Remove stressors

Concerning juvenile fish, Goldfish aren’t carnivores and won’t see these as prey unless the tank situation isn’t normal, i.e., when your fish are underfed or stressed.

Stress may be brought about by the lack of space. If the tank is too small for all those fish, the chances of stress leading to the big Goldfish eating the little one is higher.

Check your temperature. Water that’s too hot will make Goldfish stressed, too active, and sometimes gasping for air at the surface.

Can You Introduce A New Goldfish To An Old One?

You now know the appropriate sizing for a smaller Goldfish. The next question is how to start the process of keeping them together.

Can Goldfish live with smaller fish?
Can Goldfish live with smaller fish?

If your Goldfish has a history of aggression towards other Goldfish, better keep it alone or introduce just one tank mate first. On the contrary, a Goldfish showing signs of loneliness will become livelier with a compatible tankmate or tankmates.

If you want to add several Goldfish, it’s better to introduce them one at a time to see how the bigger and older Goldfish react to their presence. This gives you time to separate them if things go south, like when you see the bigger Goldfish constantly chasing the smaller ones.

Again, keep in mind that you need enough space for the new fish.

Can Goldfish Live With Smaller Fish?

We’ve answered this question in terms of Goldfish living with other Goldfish. However, other smaller types of freshwater fish may be considered tankmates.

Single-tailed Goldfish should preferably be kept with other similar Goldfish and Koi as they grow quite big. When it comes to Fancy Goldfish, they can live with smaller fish like:

  • Tetras
  • Rosy Barbs
  • Platies
  • Giant Danios
  • Corydoras

The risk here is that these smaller fish are faster and might compete with your Fancies for food. Another risk is that most of these tankmates should be kept in schools, and therefore you can’t get just one or two. If you don’t have the space, don’t consider getting other tankmates at all.

If you ask us, we’d rather you keep Fancy Goldfish with other Fancy Goldfish as there would be no risk of malnutrition or other stressors.

Big And Small, Keep Them All?

When it comes to compatibility, always put the safety and well-being of your fish first and foremost. There may be ways to keep Goldfish with smaller fish (Goldfish or other species), but always observe if they’re getting along and if all fish are staying healthy.

It might not be worth it to keep them together, so separate when you observe unsolvable problems. Don’t feel like a failure, all hobbyists know that keeping Goldfish by themselves is already a challenge in itself.

The best scenario would be to keep a similar group of Goldfish by themselves. They’ll be social, great to look at, and safer. Plus, it wouldn’t be hard to keep the tank in tip-top shape as they already make a lot of mess by themselves.

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