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.

Here’s a short video to give an idea of what spawning behaviors actually look like.

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

By |2017-12-21T02:52:56+00:00April 2nd, 2014|Breeding Koi|54 Comments

About the Author:

I have been interested in fish for over 25 years. I have two degrees in marine science with a specialization in fish ecology and physiology (as well as a chemistry minor). Like many kids, I had a goldfish growing up but decades later took care of several koi ponds. Koi are such great pets and very accessible for many folks wanting to get into owning koi in a pond environment.


  1. Finn September 11, 2014 at 10:26 pm - Reply

    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 September 15, 2014 at 3:14 pm - Reply

      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.

    • lee November 5, 2017 at 1:18 pm - Reply

      can any one help
      i’m am looking to breed 2 koi don’t really want to leave them in pond so i am asking what to put them in for hopefully breed

      • Koi-Care staff August 8, 2018 at 12:29 pm - Reply

        you can let them breed in something other than your pond such as a kiddie pool of pond water with some sort of material that will allow the eggs to attach.

  2. karl January 6, 2015 at 12:22 am - Reply

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

    • Koi-Care staff January 20, 2015 at 3:16 pm - Reply

      As long as they are eating I wouldn’t worry.

  3. Brad March 3, 2015 at 3:25 pm - Reply

    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 March 9, 2015 at 3:34 pm - Reply

      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 May 20, 2015 at 5:03 pm - Reply

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

    • Koi-Care staff June 3, 2015 at 3:47 pm - Reply

      Nothing comes to mind but I will look into it.

  5. hillary May 23, 2015 at 3:31 am - Reply

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

    • Koi-Care staff June 3, 2015 at 3:45 pm - Reply

      around 2 years of age

  6. Sabrina May 31, 2015 at 2:59 am - Reply

    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 June 3, 2015 at 3:43 pm - Reply

      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 June 19, 2015 at 10:00 am - Reply

    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 June 20, 2015 at 2:21 am - Reply

      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 June 25, 2015 at 2:32 am - Reply

    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 July 13, 2015 at 3:22 pm - Reply

      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 August 10, 2015 at 8:39 pm - Reply

    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 August 30, 2015 at 1:24 am - Reply

      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 September 15, 2015 at 10:32 am - Reply

    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 October 9, 2015 at 3:31 pm - Reply

      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 October 13, 2015 at 11:00 pm - Reply

    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 December 1, 2015 at 3:02 am - Reply

      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 October 19, 2015 at 9:36 am - Reply

    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 December 1, 2015 at 3:03 am - Reply

      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 December 29, 2015 at 2:03 pm - Reply

    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 December 30, 2015 at 8:19 pm - Reply

      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.

  14. Anthony May 3, 2016 at 1:16 am - Reply

    I recently noticed my pond skimmer mat is covered with koi eggs. I put the mat in a separate plastic tote filled with the pond water. Water temperature has been around 58 degrees in the pond and the tote. Does water temperature affect the hatching? Do you think they will hatch? Thank you.

    • Koi-Care staff July 11, 2016 at 3:36 pm - Reply

      ideally the water should be around 5 degrees warmer but animals don’t usually do something that is energetically expensive like spawning unless they are cued to do so. I think you have a good chance of seeing them hatch.

  15. Bruce Schnelle June 1, 2016 at 8:52 pm - Reply

    I have had a Koi pond for 12 years with a mix of 5 large Koi and 15 goldfish. Two years ago I had 6 fry that hatched from a plant I threw in a 25 gal barrel, but that’s the only hatch I’ve had in 12 yrs. Here’s my problem, I can’t keep plants in the pond because the Koi up root them or eat them. When the fish spawn, the eggs are laid in the plant baskets which the Koi then feed on. I’ve tried removing the planter baskets after the spawn and placing the in separate barrels, but so far no luck. What else can I try to get baby Koi or Goldfish?

    • Koi-Care staff July 11, 2016 at 3:03 pm - Reply

      Well, the kind of more professional approach involves getting your mating pair or two males and a female in a their own temporary holding tank where you can outfit it with a spawning brush or other material for the eggs to stick to. This way you can control the situation better. It is also helpful to know that goldfish will eat koi fry and koi eggs you kind of have the fox guarding the hen house there in your pond. There are also net shrouds that you can get for plants so they don’t get eaten.

  16. Joe Hougland June 15, 2016 at 2:11 am - Reply

    Roughly what percentage of hatched koi fry will end up dying? My koi spawned less than 2 weeks ago and I brought the eggs inside and put them in aquariums. I have proper aeration and small heaters to keep the water around 70 degree. They hatched about a week and a half ago and are swimming around and most are eating fry food. I’ve noticed some dead ones on the bottom of the tanks when I check on them and have been using a small siphon to remove them. I assume this is normal, but figured I’d ask. I talked to one of the local pond store owners and he said last year he only had 150 or so survive from a large sample of eggs. Any thoughts or advice? Thanks!

    • Koi-Care staff July 1, 2016 at 8:01 pm - Reply

      Just as with koi in a pond its important to keep an eye on all the usual water chemistry issues and especially with lots of fish in one aquarium you can get ammonia and nitrites build up rapidly. In the wild, yes, the survival rate is super low due to predation etc. but in an aquarium setting you should have pretty survivorship. If you are a breeder though it is pretty normal to cull quite a few as you go to remove ones you don’t want.

    • David Podor July 15, 2018 at 4:04 pm - Reply

      I have 3 100 gallon tanks that are covered with water hyacins. they all had koi eggs attached to them The fry have hatched. They are swimming around. Should I remove all or some of the hyacins

      • Koi-Care staff August 8, 2018 at 12:18 pm - Reply

        If you want to support the fry you would keep as many hyacinths as you can to give the fry hiding spots/cover.

  17. lloyd June 26, 2016 at 5:01 pm - Reply

    hi! will it be possible if i will force them to get their sperms from female and male then i will separate from another tank?

    • Koi-Care staff July 1, 2016 at 7:23 pm - Reply

      yes,some folks will manually squeeze out eggs and sperm from their fish. I think breeders do it to avoid injury to valuable females and to control the lineage of the offspring.

  18. Makenzie August 1, 2016 at 3:09 pm - Reply

    My koi fry and my adult koi are in the same pond and we do not wish to separate them how will we guarantee that the koi fry will survive

  19. mary salmons August 31, 2016 at 3:47 pm - Reply

    i have a good size pond 1200 gallons i have seen fry but all are black now young 12 month are changing colour the pond was stocked with orf koi and gold fish there has been a lot of spawning in the few months what am i breeding pond was stocked 15 years ago

  20. Alyssa October 28, 2016 at 5:27 am - Reply

    Hi, my female koi was isolated bec she had an itch, after a few days of isolation, she laid eggs. Lots of them. Do i need to put in a male koi to fertilize or should i just wait for the 2 days for it to hatch? Thanks.

    • Koi-Care staff February 3, 2017 at 8:36 pm - Reply

      They are external fertilizers so yes you would have to have a male or two to fertilize the eggs but usually they need some stimulation to release or some breeders with manually squeeze the males to get the sperm and add it to the breeding tank containing the eggs.

  21. John October 29, 2016 at 4:20 pm - Reply

    hi! I have a small kois and are larger a bit than a fry. What should I feed them? Is it okay with eggs or crushed fish pellets? Thanks in advance?

    • Koi-Care staff February 3, 2017 at 8:35 pm - Reply

      Sure, blended hardboiled eggs would be great and crushed koi chow should be fine as well. Brine shrimp are always nice too.

  22. Andy October 31, 2016 at 8:54 pm - Reply

    I have inherited a small pond with 7 koi and 1 goldfish all about 4 to 8 inch long, I noticed them chasing each other around and nudging each other in the summer, last week I saw 3 baby koi about an inch long in the margins hiding under a ledge, what should I do, separate the out into a tank for winter inside or can they be left in the pond, will they survive the cold. Help please!!

    • Koi-Care staff February 3, 2017 at 8:34 pm - Reply

      yes, they will make it through the winter. Some folks will bring them in but in nature this is the way of things. A lot of pond owners will add a de-icer to the pond to allow for a hole in the ice for improved gas exchange.

  23. Linda June 19, 2017 at 10:50 pm - Reply

    I adopted 4 koi and 1 butterfly koi last June when my boss moved across the country. My pond is close to twice the size of the pond they came from. Mine is around 16 thousand gallons with four foot of depth in the center. The fish are around 2 to 21/2 feet long. They were the only fish in the pond until today I noticed a hundred or more babies swimming around. I’ve always let my pond go through a natural selection process in the past. Between the adult fish, the turtles, frogs and water snakes that moved in on there own it keeps things from getting to over populated. I have three questions. First how many fish is a safe number for a pond that size to be healthy? I would lean towards the low end to be safe. Also with having 1 butterfly and the rest regular is there any chance I’ll get any with long fins? And lastly l bought a butterfly koi 31/2 inches long how big does it need to get to be safe to add to the pond so it won’t get ate? I want a couple more for fin verity. Thanks

    • Koi-Care staff August 8, 2018 at 12:53 pm - Reply

      to answer your question about pond capacity here is a link to my site that has a calculator- it will tell you about capacity for your situation.
      3.5 inches may be a bit small if you think you have water snakes in the pond. they may get that one.
      yes, you may end up with some long fins in the mix.


  24. Diane August 10, 2017 at 6:37 pm - Reply

    What is the process to ‘squeeze’ the Fry eggs out ?….. I am afraid of causing harm to my Koi.
    Or better to leave them to naturally spawn….

    The females are so FULL that I am concerned about their well-being. (If human I would have induced LONG AGO)!! 😛

    • Koi-Care staff August 8, 2018 at 12:42 pm - Reply

      The eggs will be resorbed.

  25. Emily August 24, 2017 at 2:43 am - Reply

    I am raising koi fry for the first time. I received them from my friend who had more eggs hatch than she had room for. I have approximately 30 fry who are around 70 days old. They have been living in a netted cage in my pond since they were about three weeks old. It is a full size pond that has catfish, sunfish and amers. I have kept them isolated to the 9ft diameter net that I made for them. I feed them 2-3 times per day. They are growing very well but my fear is they will not be big enough to release before winter. I feed the other fish twice per day but I am very worried the catfish might eat the koi. At what point am I safe to release them? Is it possible to keep them in net cage all winter? If so how deep does it need to be to survive northeast Ohio winter? I plan to use a deicer but if you have other suggestions I would appreciate any advice. Thank you!

    • Koi-Care staff August 8, 2018 at 12:39 pm - Reply

      It really depends on fat reserves to get them through winter since koi don’t eat in winter. What you could think about doing is bringing some in to a 5-75 gallons tank for the winter. keeping them in the cage with a deicer may work but generally the warmer areas of the pond are going to be the deepest parts. Catfish and goldfish will prey on them if they are small enough.

  26. Koi Karen May 12, 2018 at 9:45 pm - Reply

    I have several large koi. Water in pond got all foamy and when I went to clean filters, they were loaded with eggs, along with many attached to rocks. I placed some of the eggs in isolated area with netting. However, the eggs have a fuzzy substance building up around them. Are they bad?

    • Koi-Care staff August 8, 2018 at 12:21 pm - Reply

      No, they should be fine. Remember too that they won’t all hatch.

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