This is a question that often gets asked when new pond owners are planning on ow to stock it. On the face of it, both species can be very attractive with lots of bold colours on offer. However the route you chose needs to be dictated more than just by how pretty they look.
So, should I go for Koi or Goldfish?
When you are in the process of deciding between koi and goldfish it usually comes down to two things: how much space you have and also how much of an overall commitment you are willing to make.
While they may well look very similar at first glance, the two species have very different lifestyles. Here is the breakdown to help you decide.
The Comparison at a Glance
| Feature | Goldfish | Koi |
|---|---|---|
| Ideal Setting | Tanks or small-to-medium ponds | Large ponds only |
| Adult Size | 8–12 inches (Common/Comet) | 2–3 feet at their biggest |
| Lifespan | 10–20 years | 25–50+ years |
| Min. Depth | 18–24 inches | 4–5 feet |
| Minimum Volume | 30–50+ gallons | 1,000+ gallons |
| Cost | Budget-friendly (often sub £5 per fish) | Investment (Up to £500 per fish) |
You should choose Goldfish if…
- You have limited space: If you are looking for an indoor aquarium or a small pre-formed garden pond, goldfish really are your only option. Koi will quickly outgrow a tank and suffer from stunted growth and ongoing health issues as a consequence.
- You want low-pressure maintenance: A key point to stress here when thinking about you new pond is the fact that no fish are “no maintenance”. However goldfish are generally hardier in smaller setups and don’t require the massive and also potentially very expensive filtration systems that koi do.
- You like variety: From the sleek “Comets” to the bubbly-cheeked “Fancy” goldfish, there are hundreds of body shapes and fin styles to choose from.
You should go for Koi if…
- You have a large, deep pond: Koi need a lot of swimming room. If you are serious about building yourself a proper koi pond in your garden then it should be at least 4 feet deep to protect the fish from predators such as herons. This increased depth is also key to helping them regulate their temperature in winter.
- You want a long term pet: You will find Koi as a species are actually incredibly intelligent and can be trained to eat from your hand. Because Koi that are well kept and looked after can live for 50 years or more, they often end up become a lifelong part of the family.
- You care about “Living Art”: Koi are bred for specific patterns that are best viewed from above. High-quality koi are often treated as collectors’ items.
Can you have both?
Yes, you very much can safely and easily keep both together. They are cousins and get along peacefully. However, if you mix them, then it is vital that you build your new pond to suit the koi, and not the goldfish. A pond big enough for koi will be a paradise for goldfish, but a pond built for goldfish will eventually be a “prison” for a growing koi.
One Final Tip: Check The “Barbels” Before You Buy
If you aren’t sure which one you’re looking at in a store, then a key tip is to look at the mouth.
- Koi have “barbels” (little whiskers) on the corners of their mouths.
- Goldfish have smooth faces with no whiskers.
