How To Deal With Overpopulation Of Koi Fish Ponds: Guide To Spot Breeding Season And Be Prepared 2021

Overstocked and overpopulated koi fish ponds are very harmful to the fish. Too many fish will degrade the water quality very quickly. This will hasten the onset of disease amongst the koi.

Koi grow relatively quickly and to a large size. They spawn and fertilize usually in the spring of each year. You can sometimes detect when breeding is going to start:

• in male koi, white swellings similar to pimples appear near the  gills and along the front edges of the pectoral fins (the fins at the lower front of the koi),
• in females, their bodies swell as they fill with eggs ready for laying.

There is no way to stop the reproductive cycle but at least you can be better prepared.

The problem of overpopulation comes down to removing the babies or fry, which can be accomplished using the following approach:

1. As soon as you see that spawning has occurred, stop feeding the koi for about three weeks and let nature take its course. Basically, the adult koi will eat the fry. While this may seem cruel, it is natural and allowing it to happen allows the health of the remaining population to be maintained.
2. As an option, removing the fry very early can be considered but as well as being difficult to do in practice in any case as they will usually be inaccessible if not almost invisible, it will be hard to find an outlet through which to relocate them.
3. If the fry grows to a size where they resemble koi, then the adults will no longer see them as insects/food and at this point, the fry has to be removed for the benefit of the group.
4. Local pet stores or zoos may take them off your hands.
5. If there is a koi society in your area, they may be the best source of a new home for them.

Keeping an increased number of koi in the same environment can really damage all of them, so, cruel though part of the early steps may seem, it is one of the best options available.