Time: Late May, any year. Koi are spawning!

Call comes in from pond customer(s).

Customer says: “Hey my fish are fighting and it looks like Mr. Bubble may have fallen into my pond. The pond kinda smells a bit too…”

Pond Pro says: “Cool, congratulations!”


Why? Because it’s spawning time for koi and goldfish and the customer will soon have fish babies! So,

Congratulations!! … “It’s a fish!”

A lot of times the spawning season in our backyard koi ponds is brought to our attention because of the conditions mentioned above. Most pond owners are pretty tuned into the changes in conditions and “seasons” that every year brings us and our ponds. One of those “seasons” in our ponds, is spawning season; which typically occurs during May through June. Of course, a bit earlier or a bit later, a bit longer or a bit shorter of a spawning season depending upon where you live. And the “rules” of spawning get broken all the time when sudden condition changes occur that may trigger our fish into spawning mode out of season.

If you are not familiar with what to look for, so you can witness a koi spawning, there are some easy to recognize signs any pond owner can see.

We all know that our koi and goldfish get along very nicely, without aggression or competitiveness toward each other. This type of behavior makes up the vast majority of behavior we expect to see with our fish. Then one day spawning season hits and our fish are at each other’s throats, or at least chasing each other’s tails. The pond is full of fast, aggressive and frantic activity. The fish are chasing each other around and around, jumping clear out of the water at times, and jamming themselves into skimmer boxes, there is frantic group activity along the shoreline rockwork and plantings.

We also have pretty consistent water quality conditions with nice clear water, and a clean pond surface just about all year. Then spawning season comes to town and we see that our water quality is different. It has gotten very murky, it seems to have a slick surface quality, and the surface of the pond is also very foamy and getting foamier. The skimmer box is packed with foam, and gives out a very fishy smell when you open it. What the what!!!

Our pond’s conditions change quickly, drastically, and it isn’t all that pretty but don’t panic. Its nature and the will to survive.  Don’t try to  “treat” the water to get your normal day to day conditions right back in your pond. Step away from the de-foaming agent you are about to dump in your pond! Put down the test kit. Try to let your pond go through the entire spawning without interference. Let your filters take care of the water quality, let them do their jobs, it may not happen overnight; but they’ll do it. Your water quality will rebound to normal daily conditions, of course assuming you have proper filtration.

The rotten fish behavior we witnessed with all that aggression and chasing will soon return back to its normal day to day slow dance of color within your peaceful pond. But koi are koi, and they are going to spawn how they see fit, and there is nothing we can do to change it, even though all the males gang up and beat up the females pretty badly. The aggressive behavior is definitely stressful, sometimes deadly, to the females and you will see they get pretty beat up with torn fins and all, sometimes bloody. However, they too will typically recuperate with a little time, and also return to normal day to day activity in the pond. The female koi may not talk to the male koi for a while, but time heals all.

The smelly water, you know that pondy smelling water; well that will dissipate as well and your pond will go back to (hopefully) it’s odor free state of being. If any smell lingers then carbon will do the trick to remove foul odors.

Some fun stuff to do during the spawn is to get some photos (yes, I realize how that sounds) or video (I know how that sounds too). When the koi and goldfish calm down, go try to see some of their eggs. Koi and goldfish eggs should be visible around the shoreline rocks and plants. The eggs will be clear, round, and the size of a grain of salt, maybe a tad larger. Try to hatch some eggs indoors in a small tank of pond water and gentle aeration; you’ll be surprised how easy it is!

After the “koi and goldfish courtship” is over, take a good look at your fish to see what condition they are in. Take measures if necessary. Make sure that they are being properly aerated, especially in very foamy conditions. A good pond aerator is always good to have on hand! After they have calmed down give a good rinse to filter pads they will be pretty nasty.

Just a few weeks you will likely start seeing darting little koi and goldfish fry around the edges of your pond; swimming in and out of the rockwork and plants where they will grow out until they are real deal baby fish. A short few months later, colorful little koi will be milling in with the bigger koi trying to get in on some of those delicious pellets being served up; and it will make you happy.

So, that is why the pond professional told the customer “congratulations” when the customer thought that their pond had gone completely off the deep end!

“Congratulations … it’s a fish!”

by: Mike Gannon

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