I’ve got koi fry –now what!? A step wise approach to raising baby koi

got koi fry

If you just noticed that your pond now has a million little koi fry swimming around then skip down to the feeding section but if you haven’t bred koi yet and need an introduction then read on. Spawning typically occurs in the early summer months and is very water temperature dependent – 68 degrees F is the minimum for spawning .  Your adult koi will have to be sexually mature to engage in successful mating and this typically occurs at age 2 for males and at age 3 for females.  Keep in mind when you are selecting the parents that the larger the female, the more eggs she can produce.  If you are wondering about how to tell the sex of your koi, there are different approaches to this such as looking at pectoral fin shape and size but the tried and true method is to inspect the underside of your koi.  If there is one vent (slit) then you have a male, if you have two vents (slits) then you have a female.  Usually spawning activity, and the behaviors associated with it, will take place in the early morning and may only last 30 minutes.  The whole process is a bit rough as the male needs to physically stimulate the eggs to be released by nudging the female’s belly.  After eggs are released, the male fertilizes them by releasing sperm.

Breeding Material

If you plan on having a dedicated spawning tank you will most certainly want breeding material.  This is simply material that offers surface area for the eggs to stick to.  This could take the shape of aquatic plants, ropes, a “spawning brush” or a “spawning mop”.  Most importantly it needs to be something that won’t be toxic in any way and has lots of surface area for eggs to attach.  You will want to have plenty of breeding material for the eggs to attach to-maybe around 50 to 60 percent of the bottom of the spawning tank should be covered.  The size of your spawning tank will depend on how many fish you plan on trying to get to reproduce.  It should be something on the order of 1 to 2 feet deep and maybe 6 feet by 6 feet –some hobbyists have used inflatable kiddie pools with success. After eggs have been laid and adults removed from spawning tank you should see hatching around 4 days later.  When you are satisfied with the density of hatched fish you can remove the breeding material.  So what will the eggs look like? See below.

example of koi eggs

Thanks to Anthony R. for submitting these pis of his koi’s eggs

Tank/Pond Conditions

You may choose not to go with a separate fry tank or pond and simply let it happen in the main pond.  If this is the case be aware that if you have goldfish amongst your adult koi you will have some egg loss due to the goldfish’s appetite for koi eggs.  Your koi eggs will hatch around 4 days after they are fertilized.  They will then attach themselves to structure like the side of the tank or pond for 2-3 days where they will be feeding off their yolk sac. If you are seeing a great deal of swimming koi fry and also a lot of eggs at the bottom feel free to remove those as they most likely failed to fertilize and will only drive ammonia levels up.  Be sure to monitor all your water chemistry, especially ammonia and pH.

What to feed your koi fry?

At around the 10th day (sooner depending on water temp) you will notice your koi fry trying out their new-found ability to swim and it’s at that time that feeding should begin.  A lot of koi enthusiasts will start off with something called “infusoria” which is not a thing but more of a size classification.  Generally, it’s defined as very small aquatic organisms and for koi fry those should be live daphnia (water fleas) and/or brine shrimp (“sea monkies”).  If you can’t obtain infusoria you can try chicken eggs. Boil the eggs (some just use the yolks) and, in a blender, mix with about 30 or so ounces of water from the tank or pond.  Simply squirt that mixture over the surface of your breeding tank or pond.  You will want to feed around 4 times per day.  In general you are trying to match the size of the food with the koi fry such that it is an appropriate size for them to eat. After about a week of this mixture you can switch to a powder called “fry powder” which can be sprinkled over the water’s surface.  You can also use standard protein infused koi pellets and basically grind them up into a fine powder and select for a certain grain size by shaking it through a sieve.  It may take a few days for the fry to associate the new powder with food and acquire a taste for it. Be sure to clean the bottom of the tank for any waste and excess/uneaten food –you really want to avoid ammonia build up. Make sure that you provide plenty of aeration for your koi fry and this is especially true in the summer when warmer water temps mean less oxygen carrying capacity of water. Some other foods that you can feed are frozen brine shrimp, growing live brine shimp in your containment tank or main pond and freeze-dried krill. You may also add, as a nutritional supplement, spirulina powder and wheat germ.

brine shrimp (sea monkey)

Daphnia water flea copy


One mistake people make is trying to keep all the koi fry, that’s a bad idea. You definitely want to “thin out the herd” because by doing so you create a more healthy environment for the remaining koi. Your first round of culling should take place at around 1 inch or 25mm. This should fall at about 4 weeks (possibly longer) after swimming is first observed. Another culling should take place a month after the first or about when they are about 2.5 inches or 6.25cm. The first and second culling should remove about 80% of the initial population. Additionally, a third culling should start a month after the second one and remove 50 to 60% of what’s left (see the “Breeding Timeline” below). When culling you should be looking for deformities, undesirable coloration, erratic swimming, sluggish swimmers and generally undesirable traits. You don’t necessarily have to euthanize these fish-give some to your friends!

Final thoughts

When your koi do finally make it to a larger size and you want to introduce them to the main pond be aware that adult koi will eat most anything and the baby koi might be on the menu if they are small enough. Be sure to release them only when they are big enough that they won’t actually fit in the adults mouths!

Typical Timeline for Koi Fry

Typical Timeline for Koi Fry

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26 Responses to I’ve got koi fry –now what!? A step wise approach to raising baby koi

  1. Finn says:

    I have two large koi in an ~ 4000 gal. pond. I have been offered two large adult koi and don’t know how the current alpha koi will react to another daily . The two adults I have seem to reproduce every time they possibly can and I have never seen them eat the baby koi or baby goldfish. Any advice?

    • Koi-Care staff says:

      I guess that will depend on your own goals. Are you wanting to shake it up a bit and get some more genetic diversity in the mix? Do you simply wish to have more koi to look at? From my perspective, if you have a system that works and you are happy with how the breeding is going and the fish seem content I would be hesitant to rock the boat ( but I also think that when it comes to koi in ponds that less is more).
      There will most likely be some degree of conflict amongst the males especially during breeding but that’s just the way of things. More importantly though is that you don’t want your female to become injured or stressed from the conflict – they usually take the brunt of the injuries when males are jockeying for top spot in the breeding pecking order.

  2. karl says:

    Hi my koi fry will only eat off the bottom on the tank should I be concerned?

  3. Brad says:

    I just bought 60 small koi 2 inches long, I was wondering how much I should feed them and how do I know which ones to cull as they all look healthy and all have roughly the same pattern however some are common and some are mirror, thanks

    • Koi-Care staff says:

      As for the culling procedures that is entirely up to you what colors and traits you want to keep. Colors and patterns can change as they develop so you may want to wait and see. Obviously you will want to remove any that look to have any kind of swimming or health issues. As for the food you could use a food from Laguna called “Laguna goldfish and koi food” -its suitable for fish 1.5 to 3″ long.

  4. Bonnie says:

    is there a food to feed my five, large, over 25 lbs. each Koi so they stop reproducing?

  5. hillary says:

    How old do koi have to be to be able to breed and produce eggs?

  6. Sabrina says:

    I took my koi eggs out of my pond and put them in a bucket. I saw some hatch and they were swimming with a few hours. Problem is I dont know much about caring for eggs. Can I keep them in the bucket ?

    • Koi-Care staff says:

      you could keep them in a bucket but you will need to address aeration and water quality issues just as you would with your pond. The way around it is to have your fry in a mesh pen in your pond -that way you gain the benefits of filtration and aeration from your pond while keeping fry out of the intake and free from predation

  7. brad says:

    I Have had my first successful spawning in my new pond (1.5 years matured) and i now have a lively bunch of fry in a separate tank indoors.the eggs were attached to a load of elodea which was free floating. i removed all the elodea and placed them in my tank to hatch . i have now removed the elodea as the fish are free swimming but they left a load of debris on the bottom of the tank full of hatching flies that look to be white in colour. firstly what flies am i seeing hatching ? 2 – i want to remove the debris and do a little water change (removing dead eggs, fish and plant waste) but i am paranoid about sucking fry up in the syphon. any suggestions to minimise fry loss ? also i am hatching brine shrimp. roughly around 5000 eggs every 2 days (200 litre tank with app 100 fry). should i be supllementing with theese aswell as a four a day feed schedule with eggs yolk ? or could the egg yolk be drpped to the amount of brine shrimp in the water ?

    any advice would be appreciated

    • Koi-Care staff says:

      flies? not sure about that. Not sucking up your fry can be difficult when you are trying to keep everything clean. You are going to cull a lot of them anyway so I would just try to limit how much you actually siphon in the tank and you may happen to suck some up. I would reduce the egg if you have a good source of shrimp-that will ultimately be a better and more complete food source. If you have a mop and want to keep grabbing the spawn then I would remove the weed. Good luck!

  8. Kim says:

    My koi spawned about a week ago…I added some lettuce plants in hopes of saving some of the fry from being eaten by the adults. My water levels seem to be out of wack now. Is this common? My nitrites and nitrates have both elevated slightly. My ph has dropped to 6.0 and my amonia has raised to 4.0. I added a good amount of well water, some stress coat with metal removers and about 6-8 cups of salt to the almost 3000 gallon pond. I cleaned the filters as well. Will things start to level back off or do I need to do continuous small water changes daily? Any other suggestion would be appreciated.

    • Koi-Care staff says:

      You def. Don’t want your ammonia to be that high. Ammonia is especially hard on koi gills. One thing I would point out is that a lot of pond owners will clean out their filters quite often but when that’s done the beneficial bacteria are also removed. So one thing I would do is boost your beneficial bacteria load by adding something like microbe-lift pl. Regular water changes are def. A good thing in this case. It would also help in the future if you spawned your fish in separate holding tanks- that way you don’t have to worry about losing fry and fry getting in your intake. Just for fun you may also want to test your well water.

  9. Matt Tolbert says:

    I have 14 fry that are about 3 weeks old in a 5 gallon aquarium. I feed them crushed up flake food twice a day. I change 25% of the water once a week. I have an air stone. I also have algae from the pond. I’m thinking of starting to feed them brine shrimp as well.

    Anything else you’d recommend?


    • Koi-Care staff says:

      You could also add in the spirulina supplement -its very standard among breeders and aquarists so it shouldn’t be hard to get.

  10. Franco says:

    So im quite new to the koi thing my parents built a show pond and got a few koi avg 30 to 60 cm but they stared spawning and i dont know how to separate the fry from the adults can i use nets or is it a must to incorporate a free standing tank ???

    • Koi-Care staff says:

      It really helps to have them in their own holding pen. That way you can avoid predation by other aquatic creatures as well as other koi. It also helps you to cull the koi much better. Most likely they will be mixed up in your aquatic plants for shelter so try to say use a bucket to kind of suck them in. The less stress you cause the better.

  11. Melissa says:

    I brought some of my fry in for the winter (late July spawning due to water change ) I have about 30 in a 150 stock tank .first of all is that to many for the winter . I have 500gph sunsun filter going and water quality is fine . they are pretty small now just wondering for future months . Mainly I was curious I have noticed one with what looks like a crooked spine. He swims not well . Eats good I make sure it’s near him just in case . Is he hurt ? Birth defect ? What is the best procedure to take ? Is it purely physical and unperfered or is it actually harmful or mean to keep the fish ? Please advise as to wether/how to put him down or just keep a eye on him a while … This my first year with koi so it’s a definate learning experience thanks so much !

    • Koi-Care staff says:

      that number of fish will be fine, if you had adults you could do about 4-5 inches of koi in a volume like that. Just keep an eye on ammonia and the usual water chemistry metrics. As far as your bent koi its not uncommon to see that in a large group of fry and it terms of euthanizing it that’s up to you but as long as it can compete enough to get food it should be fine. if you were a breeder that fish would be culled for sure. Some would call it a defect and some would call it “character” -just depends on what your focus is in having koi.

  12. Peter says:

    I have had KOIs for more than four years now, but moved from an estate house to a plot 8 months back. I converted the previous owners big natural like duck pond into a Koi pond. A week ago I discovered hundreds of Koi fry in the pond, the pond is in a bush like setting with lots of water plants and mud, the water quality is mostly good because it comes from a borehole. I put the net to ensure that birds do not eat the fish but do not know what to do next. Help!!!!

    • Koi-Care staff says:

      Peter, lots of folks have ponds with fish that they never really tend to and the pond just does what it does naturally so your next step will depend on what you want to do with the pond. Protecting the fish from birds is a good first step but are you wanting to get into breeding? If so you will want to start culling fish so you don’t end up with undesirable types or color patterns. Or you can not cull any but will you have the food stores to sustain the fish? If you have netting and the pond is spring fed and you have lots of plants (i.e. cover for fish to hide in) then my answer is “not much”. Aside from feeding and keeping an eye on water quality I think you have a nice little community of koi.

  13. Liz says:

    Thanks for all the great info. Our koi have little babies. We separated them out today. We’ve only had the pond a couple of months so really pleased. We fended off the hungry grey heron and all are happy. But – we also have some small fish that we can’t explain how they got there. They are silver and more round shaped than the koi. About the same size which is around 1cm long. How? What? ,!!!

    • Koi-Care staff says:

      Not sure what kind of fish you have mixed in there but the leading theory on how they get in there is via eggs attached to the legs of wading birds. So birds like your hungry heron wades through a pond and inadvertently walks through some fish eggs attached to some aquatic plants, gets some eggs attached then flys away to another pond. It might be interesting to see what it turns out to be.

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