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Determining if Your Koi Are Male or Female

Distinguishing between Male & Female Koi Fish San Diego, CA

There’s an emerging trend in the high-end segment of the Southern California real estate market, and it’s centered on the kind of extra features that can make properties really unique. In August 2021, a Malibu real estate brokerage listed an $11 million mansion on a hill overlooking the Pacific Ocean. One of the most interesting features of the property was a Japanese Zen garden complete with a koi pond stocked with exotic species. Realtors are now getting more clients with deeper pockets who are specifically asking for established garden ponds they can readily take over. Koi breeders are also seeing increased business from pond keepers who figure they can list their properties at higher prices if they offer a nice mix of koi variants.

Now’s a good time for koi pond keepers to get into breeding. If you wish to explore this activity, you’ll need a koi couple swimming in your pond when spring starts, which means you need to distinguish between male and female. Luckily, this isn’t very difficult. The friendly and knowledgeable staff at Aquatic Warehouse, a leading provider of koi pond supplies, are here to share some details on how to tell male and female koi apart.


The brighter coloration of male koi is a trait linked to mating. Similar to other aquatic species, male koi tend to exhibit a more attractive appearance to catch the attention of fertile females. You can see male koi become more colorful as temperatures rise. Their colored patterns will be more subdued in the weeks following insemination.


This is probably a better indicator of koi sex because it’s purely anatomical. When koi become more mature, usually after 4 years of age, the fins of female koi are invariably rounded, larger, and not as colorful as their male counterparts. In many cases, female fins are translucent, although some will have one or two spots of color. The fins of male koi are pointed, and they tend to be almost solid with color. During their mating and breeding periods, male koi will grow small white spots, which are actually tubercules, on their fins, but you won’t see them on females

Body Shape

The larger and most striking koi that are bred for exhibition purposes tend to sell for thousands of dollars, and they’re more likely to be female. You may think of this as a contradiction because males are more colorful, but their anatomy isn’t conducive to exhibitions. Female koi are larger and rounder. They’re shaped like blimps, whereas males are shaped more like French baguettes. This larger surface area lets breeders show off more colors, patterns, and shiny scales.

Breeding Behavior

There’s a chance you may already have koi couples in your pond, and this is when it’s easier to tell them apart in terms of their sex. Once a female is fertile, she will hint her state to the males she is attracted to, and this is when a mating pursuit will arise. The males will chase after the females. There may be some fighting among males, but nothing that results in dangerous violence.

Regardless of whether your koi are male or female, caring for them properly includes having all of the necessary pond supplies on hand. At Aquatic Warehouse, we carry pond filters, pumps, vacuums, nutritious koi food, and everything else you need to keep your koi happy and healthy for many years to come. Stop by our store in Kearny Mesa, order the supplies you need from our website, or give us a call at 858-467-9297 if you have any questions.


Contact Information

  • Address: 5466 Complex Street Suite 204
    San Diego, CA 92123
  • Phone: (858) 467-9297
  • Email: sales@aquaticwarehouse.com
  • Working Days/Hours: Mon - Fri / 10:00 AM - 7:00 PM
    Saturday / 10:00 AM - 6:00 PM
    Sunday / 11:00 AM - 6:00 PM


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