Clash of the Carp Cousins: Koi Fish vs Goldfish

Koi fish versus goldfish.

How are koi fish and goldfish related? How are they similar and how are they different? Can you cross koi fish and goldfish? Learn more about koi fish vs goldfish.

Koi fish vs goldfish.

Koi Fish vs Goldfish: Origin Story

Both koi fish and goldfish are members of the carp family and originate from aquaculture in ancient times. Goldfish (Carassius auratus) originate from the Crucian Carp (Carassius carassius), native to freshwaters across Europe and Russia. Koi fish (Cyprinus rubrofuscus) originate from the Common Carp (Cyprinus carpio), native to Europe and Asia and has been introduced other places. Both fish were originally farmed as a hardy food source. However, some fish were noted with outstanding colors and set aside. Over countless breedings of these “special” fish, we have the koi and goldfish we know today.

Koi Fish vs Goldfish: Anatomy

Although they can look VERY similar, there are a few differences when it comes to comparing the external anatomy of a koi fish vs a goldfish. We have many owners who confuse the two, and it just takes experience looking at LOTS of fish to be able to tell the difference immediately. When they are small and developing, it can be VERY hard to distinguish between the two, which can be a difficult situation if you are expecting goldfish and end up with koi fish.

Koi Fish External Anatomy

Koi fish typically have a box-shaped head and longer, more slender body. However, if your goldfish is emaciated, they can look almost identical. On the underside of their mouth, koi have prominent barbels or whiskers, typically found as two pairs.

A koi fish swimming in a pond with barbels.

Goldfish External Anatomy

Goldfish have shorted, rounder bodies and do not have the barbels on their faces. If you have reproductively-active goldfish, note the breeding tubercules on the sides of the operculum and pectoral fins, present in males, but not females.

But goldfish and koi fish have different colors?

Yes, most goldfish are orange or white and most koi have a mix of colors, but not always. We have seen some very vibrantly colored goldfish and some very plain-looking koi. Relying on coloration alone is not much help when it comes to distinguishing koi and goldfish.

Keeping Koi Fish vs Goldfish

When it comes to keeping koi fish or goldfish, their care is almost identical. They both have the same water quality ranges, dietary preferences and are both very community-minded fishes. The biggest difference is how much space they will required. Goldfish can start out in about 20 gallons per fish, but may require 50 or even 100 gallons per fish when full grown. Koi require at least 250 gallons per fish and that increase to 500 gallons per fish for reproductively-active females. If you have a smaller pond, it is highly recommended to stick to goldfish rather than koi. (If you have a tank – why would you even consider putting koi in it?)

Both koi fish and goldfish require a lot of filtration, so keep in mind that any pond filter you buy might want to accommodate TWICE your pond’s volume to ensure all of their waste is processed. From what we have seen, goldfish are a bit messier than koi, but don’t hold that against them.

When it comes to the lifespan of a koi versus a goldfish, you are looking at a few decades for each. Koi will typically live longer than goldfish by at least 10 years. Goldfish, at least the long-body common and comet varieties, expect to get to 20 years. For koi, you can get them into their 30s easily, even 40 and beyond. Our oldest koi patient is 37 years old!

The most common cause of death in older pond fish? Someone leaves the hose running while refilling, gets distracted and forgets to turn off the water for several hours. On city water, this results in chlorine toxicity, which there is no treatment for. Best advice: never leave your pond while filling!

Can Koi Fish and Goldfish Cross Breed?

Producing koi fish and goldfish hybrid species has been accomplished most frequently by artificial spawning for research purposes. This will lead to offspring that are sterile or diploid, containing two complete sets of chromosomes (rather than one from each parent). It has occurred very rarely in wild and captive populations.

Can I Keep Koi Fish and Goldfish Together?

Yes, you can absolutely keep koi fish and goldfish together. They share almost all of the same diseases (except a few herpesviruses), enjoy the same water chemistry, diet and friends.

Very frequently, pond owners will start their pond with $0.25 starter goldfish, assuming that at one point, the goldfish will be rehomed. Do you know how often that actually happens? Not very often! Good luck catching those goldfish! If you want to hire us to catch them, that’s one thing; because we’re AMAZING at catching fish, but awfully expensive. Thankfully, it is perfectly fine to leave your started fish in with your new koi.

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