How much exactly do you know about koi reproduction? For a lot of pond owners, these particular habits of their fish are not something they consider. But, when you look into it there are a lot of interesting facets of koi biology.

We at Pond and Garden Depot are here to answer the burning questions you've always had about koi - how they reproduce, can they interbreed with goldfish, and more!

Can koi and goldfish interbreed?

We all know about "the birds and the bees" but what about "the koi and the goldfish?" Well, as it turns out, koi and goldfish are actually both related to the common carp, meaning that they can indeed interbreed. These goldfish-koi hybrids are similar to mules - they have characteristics of both of their parents and are unable to reproduce. These hybrids tend to be somewhere in-between the size of goldfish and koi. There are many different names for different combinations of parents, from Koibunkin (Shubunkin-koi hybrids) to Koimets (Comet-koi hybrids) and many more!

How can I tell a koi's sex?

It can be hard to tell the sex of a koi without knowing what to look for. The main way to tell the sex of a koi is the shape of their body and fins. Male koi have smaller, pointed fins that are usually very colorful, while females have more rounded fins that are often colorless or even translucent. The males also tend to have a more thin build, while the females are more rounded, stockier, and generally larger overall. It is also very difficult to tell the sex of koi before they reach maturity, as the differences between them become much more pronounced at that point. By the time they are 10 inches long (or about three years old), they will be mature and it will be much easier to identify their sex.

How does spawning work?

Rather than giving live birth - which is rare among fish - female koi lay large clutches of eggs which are then fertilized by the males. When koi spawn, they can lay up to 100,000 eggs, the vast majority of which will be eaten before they hatch (sometimes by their own parents!) The time that fish spawn is determined by the temperature of the water, typically occurring when it reaches 65° to 70°F, which is usually between the months of May and June.

Why are my male koi chasing around the females?

Have you noticed your male koi following the females and bumping into them? The reason for this is that the males can tell that the females are about to spawn, and they want this process to be sped up as much as possible. When spawning time approaches, male koi will begin to chase after the females, nudging their sides and acting generally aggressive. Now, that's not my idea of a great first date, but apparently, it works for Koi! And while this might seem quite rude, this is actually a natural behavior of koi, and the reason they do this is to "encourage" the females to lay their eggs so that they can be fertilized.