Ever wondered if you have male or female koi?
Do male and female koi look different? In subtle ways – yes! Here are several ways to tell if you have boy fish or girl fish.
Body Shape
I find that shape is a really good place to start. Female koi are rounder overall. Think “plump and proud”. Males are sleeker, more torpedo-shaped. Going from head to tail, right before the vent is thicker before the body slenders to the tail. (Apparently “slenders” isn’t a word. But it makes sense to me!)
This long, sleek looking blue fish looks like a male.
Fin Shape - male or female?
Take a look at the fins nearest the head. Males have more pointed fins and sometimes longer. Females pectoral fins are rounder and may be more transparent towards the ends. Sometimes looking at fins this way makes it easy to tell, but sometimes it doesn’t . I mean what about a Butterfly Koi? What then?
This beautiful white and red fish was named “Houlihan” for her Hot Lips! Her shape gives a clue that she is female. She is not shaped like a torpedo, she is plumper before her tail. Look at her pectoral fins. Roundish and somewhat transparent on the edges. It may be difficult to see, but can you tell that the orange fish has more pointy fins and a more torpedo like shape? Yep – male fish!
The Vent
Have you ever heard (read, or seen in a video) that you can look at their vent to tell (the area under the tail)? Supposedly, a female’s is more pink and “protruding”. But let’s be real—unless you’re planning a koi spa day complete with gentle handling and a headlamp, most of us are not flipping our fish over to look at their vents!
This is a picture of a male koi vent. (We did not show his face to protect his privacy).
This photo is of a female koi vent.
Do you feel like an expert on fish vents now? No? Me neither!
What About Koi Eating Behavior?
I read that females koi tend to feed near the surface and are more aggressive when eating. Males are less aggressive eaters and prefer to eat mid-water or on the pond bottom. Alright, but I feel like when I feed my fish they all come up and go nuts! Now if I have smaller fish in the pond with the larger fish. The 4 to 6 inch fish will let the large fish go nuts at the top first so they don’t get trampled by the big guys. Have you noticed certain fish eating differently in your pond?
Here is a great example of a pectoral fin that is very round and transparent on the ends.
Other Things to know about Koi
Did you know female koi can grow to be larger adults? Yes! Even up to 12 inches longer!
Wondering when they will start to make baby fish (called fry)? Koi don’t start breeding until they are 2 to 3 years old. It’s true!
Fish need the water temperature to be between 65 and 75 degrees for them to breed. Yes! And they can lay 5,000 to 10,000 eggs ore more! Koi love to snack on the eggs though. When some fry make it, the larger fish wont bother them when they grow to be around 4 inches long. In our pond we have only gotten 5 or so new fish each year. Goldfish, however, seem to have more babies that live to be adults.
If you want to add to your flock of fish (actually called a “shoal”) you do have to take precautions. Read about how to Transfer Fish From Another Pond.
Kristi's Tips
When it is rainy and overcast – look out for HERON! They love that weather and tend to show up to eat our fish. It may be because the water is easier to see through when it is overcast. If you are looking at your water hyacinth and wondering why it isn’t looking great, it’s because the water temperature isn’t as warm as it likes. When it warms up here it will start making little clones of itself and looking great!
Did you know that male koi generally have thicker barbels than females? Yepperdoodles.
*No koi were harmed in the making of this content, although they were definitely inconvenienced and potentially embarrassed.