A Birth and a Miracle of Design


Duncan Griffiths

Copyright © 2005 koi-unleashed. All rights reserved


Given the time of year and events that may be forthcoming in koi ponds all over the world,I though it appropriate and fitting to write a little introduction to the birth of our koi and the spawning process, as many of you may fancy having a go in the spring


I know I find it fascinating and I can't be alone in this. I get a buzz every time I go down to check on some spawn to see if its hatched yet, to be greeted by what look like minute splinters of glass with two black dots tumbling all over the tank. And I am sure I will never lose the attraction for this wonderful sight.


For those who do not have the time to dedicate themselves to the enormous amount of time it takes to raise these little critters to become living jewels stop now, it is a time consuming and all consuming pastime.


In early spring mature male and female koi will be coming into the breeding season after the winter, this is bought about by the lengthening hours of daylight, the temperature rising, food being fed regularly and being of high quality and dissolved oxygen being maintained at a high level. Once these condition are met the koi's physiology will begin maturing and adding to the spawn load she carries and the male will be doing the same. This is caused by the release of Gonadotropina hormone, released from the pituitary gland when conditions are right. A carp can spawn more than once a year and if spawned in the spring can spawn again later in the year.

A gravid female is easy to recognise, being swollen around the vent area with the swelling being mostly symmetrical on both sides.This will be evident in the region from the vent up to the ventral fins and just a bit beyond (in a natural looking way). Where as the male will to a larger extent retain its manly physique.


At some point when the temperature hits around 20į C, give or take, and the daylight hours are stretching out, a spawning event will take place. This usually takes place when some kind of pond event happens that is out of the norm; it could be a heavy shower, a sudden drop in temperature, even a large water change can cause spawning to take place. Very little is known about exactly what triggers the final spawn. The female will send out pheromones (a scent) which will drive the males nuts and finish the maturity of its sperm and the male will then chase the female along with other males in an attempt to mate and be the one to pass on his genetics to the egg and therefore the offspring. They can be seen constantly nudging the female.


This is quite a brutal affair because unlike most fish the gravid female koi cannot lay eggs they have to be driven out of her by a male. In salmon the female cuts a nest and lays her eggs; shortly after, the male deposits the milt over them. Not so with a koi carp.The male must expel the eggs from the female otherwise they stop where they are. And, this is very brutal and can result in damage to both partners


The female will look for weed or anything that she can deposit her eggs on but in the absence of anything she will simply let the male dispel them from her anywhere and they will likely stick to the walls of the pond.

In the wild, the male will chase the female into the shallows and once trapped he will nudge the spawn out of her. In a pond they are usually not so lucky so it becomes free for all unless you intervene.


For the record eggs are known as spawn and sperm is known as milt.


The male nudges the eggs out of the female and fertilises them as they come, once the eggs hit the water four things happen. First the egg is viable for fertilisation for around 30 seconds to 2 minutes max with it more likely to normally be around 30 seconds to 1 minute; once this predetermined elapsed time has gone the egg cannot be fertilized. Second the egg begins to absorb water and swell to around x4 its original size. The egg, as it leaves the ovary duct, is around 0.5 mm once it swells it will be around just less than 2 mm.Third, the egg also becomes very sticky and will adhere to any surface. Fourth, once the spawning is complete the very next thing the koi will do despite being tried is eat the spawn. Make no mistake they will eat the lot till the scent of the eggs has vanished


In around 4-5 days time, 7 at the outside, the fry will immerge and yet again the koi will set about eating the newly emerging fry.They are not very good parents.


Letís explain the fertilisation process a little further:


The female is capable of carrying around 100.000 eggs for every 1kg of body weight. So a female of 10kg in weight will pass 1,000,000 eggs of which 60% will hatch.


The male produces less milt by comparison, but there is a phenomenon which is peculiar to both male and female. In the female, the egg only becomes capable of fertilisation when it hits the open water and with the male the sperm only becomes active once that hits open water, once this has happened the clock is ticking and the race is on for fertilisation.


Unlike the human egg where the sperm has to penetrate the egg, and once the head of the sperm is in the egg the tail gets left behind. The koi egg has a very tiny hole/entrance in it called a micropyle and the koi sperm swims into the mycropyle. Once there, the egg entrance closes, the entrancestart closing on contact with open water so the process must start instantly and be completed in a seconds.


The sperm also becomes active on contact with open water and the sperm will also only be mobile for around 30 seconds, so the sperm cannot afford to hang around otherwise the entrance to the egg will be closed and the sperm will die.



The sperm enters the egg; the mycropyle and entrance seals, the eggs swells and becomes sticky, very sticky and attaches to a plant or spawning media. At this point the genetics are set and either a good fish or a poor fish will develop


The egg will then start to divide and over the next few days the embryo will develop, at 2 days you can clearly see two black dots shining through the case which will be the eyes, if you take one of the viable eggs and put it under a microscope at x40 you will be amazed, you can see the developing fish moving and its heart beating quite clearly.


Mother Nature is a wonderful thing she has thought of everything. She knows the developing eggs are very vulnerable to predation and so the biology of the eggs gestation is geared to hatch the young fry ASAP before the egg gets eaten.

Dependent on temperature, the egg will hatch in around 5/6 days but the poor little fry has not really had time to develop, but the longer it stayed in the egg the bigger the chance of being eaten, so mother nature again has equipped the newly emerged fry with only the bare essential but everything the fry needs to survive the next few days while further development takes place


Nature has rushed things a tad and although the fry is out of the egg and past that danger itís not completely out of woods from the predation aspect and is still very vulnerable.


The new hatchling has one fin that goes right round the central line of its body, kind of like an eel to give it some mobility, its gills are not developed so the fry is capable of taking in oxygen through its skin, it has no mouth so it has its yolk sack from the egg still attached, which it will feed off for the first few days, because it has no mouth it also has no use for an anus yet, so that will develop over the next few days. What it does have is huge black eyes for seeing Bruce the great white coming to eat it. Because it's not that mobile it has a sucker on its head so the newly hatched fry heads under a rock and attaches itself to the surface and hides there; while its development continues.

In the wild here it will stay few a few days until it has its, mouth formed along with some of its fins (not all) also its anus, swim bladder and gills. By this time the eggs sack has gone and the next thing it will do is swim up to the surface take its very first gulp of air to fill its swim bladder and from here on in itís an almost fully functional fish and will start feeding on solids via the mouth


So for the first few days we do not need to feed, we do not need to feed until its come up for its first gulp of air.

It still has predation issues but it is almost fully mobile with full sight and can feed and run for cover.


Nature has packed the development of this individual fish into a few days what takes years for other species of animals to achieve, to endure carps survival in a very hostile world.


So you want to breed some fish?

You first have to decide if you want natural spawning or induced artificial spawning?


In practice the former usually occurs before you are prepared and you end up extracting a few eggs for incubation, you can transfer a suitable female and male to a totally fresh environment and spawning usually takes place right away, usually within the night. This is due to unscented waters with no confusing chemical messengers The male gets the scent of the pheromones with no interfering chemical messages also the complete change of environment in itself can trigger the spawning.


I know a guy who breeds koi and he tells me he separates the males and female and either sprays water on the pond from a hose for a few hours or does a massive 50% water change, the sudden change in the temperature is enough to trigger the response and spawning begins, usually in the night or early morning, so be up early.


It's usual to use two or three males to one female to ensure good fertilization and if one does not respond one of the other might; as soon as one starts though, generally they all start.


What do you need?


Ideally you need two spawning tanks. One, for the spawning to take place in, of adequate size. Another to remove the fish to before they start eating the spawn and to rest up.


Do not put these fish straight back in the pond as the scent from the spawning process will drive the others into a spawning frenzy. You will also need some kind of spawning media, spawning ropes etc. for the eggs to be deposited on.


Once spawning has taken place remove the fish to another holding tank, if you cannot afford the luxury of two breeding tanks you must remove the spawn to another tank to be incubated


We will assume you have separated mum and dad from the eggs and the eggs are on their own now, ready to be incubated. An ideal temperature for hatching is around 20į C you can go higher to about 23į C but no more


The lower the temperature, the slower the hatch rate; the higher the temperature, the faster the hatch rate.

Be aware, there will be plenty of unviable eggs that will soon die and not only will be breeding ground for bacteria and fungus but these will quickly infect other eggs.The higher the temperature of incubation, the faster these adverse infections will occur and also the faster the decomposition of the unviable eggs and water fowling will take place with obvious consequences.


A prophylactic treatment of eggs is very advisable with an anti fungus treatment as soon as things have settled down in the incubation period (day two is ideal)

For this we use Malachite green or Methylene blue at a higher concentration than is normal for therapeutic fish treatments. The eggs and their contents are quite safe as long as the fry has not started to emerge.

This kills off any fungus on dead eggs and stops its spread to viable eggs (this is very important)

Then around 5 days later the fry will emerge. Look very carefully for them.They are very small and translucent.With a light tap in the tank side ( not to often), you will see them spin on the tank floor.


Before we get to raising them we will look at the other method of fertilisation.


For those who have limited space and resource and need total control over the spawning process artificial spawning with hormones is possible.


This involves the injection into the abdominal cavity with any one of three hormones.


Carp pituitary extract (CPE)

(Consult your local vet)


CPE is obtained from agricultural pharmaceutical companies via your friendly vet. Suppliers obtain this hormone from the carp pituitary gland situated under the carp brain. It is supplied as a powder that needs reconstituting with sterile water or saline.Injections are at the rate of 0.3 mg/kg of body weight. 18 hours after the first, a second injection is given at 3 mg /kg. 10 hours after the second injection, manual spawning can be attempted.


Care must be taken not to apply too much pressure to the abdomen of the koi to strip the eggs, as damage can easily result.If the eggs will come, they will take no effort at all, in fact just lifting the koi may displace lots or the entire spawn.

Luteinizing Ė release hormone LH-RH (a)


LH-RH (a) hormone comes in at a higher command level than pituitary and is the hormone that comes from the hypothalamus. The release of this hormone kick starts the pituitary gland into action.


Dosing is at 5 mg/kg of body weight, two injections 18 hours apart



H.C.G. Human Chorionic Gonadotropin


As the name implies, this originates from humans and can be used to spawn fish. H.C.G. is at a lower command level than pituitary extract and is the hormone (Gonadotropin) that the pituitary gland excretes to stimulate ovaries and testes to mature. H.C.G. is highly recommended and is cost effective for koi that are ripe to spawn.


Dosing is at 800 IU/kg body weight, where IU = micrograms.

1 gram = 1000 milligrams. 1 milligram = 1000 micrograms; 1,000,000 micrograms = 1 gram



Do not try to force any eggs from the female; this will surely result in rupture of the ovaries and cause sudden death. Only the very lightest pressure should be applied in all cases of eggs stripping, if they do not come with only the lightest of pressure they are not going to come at that time.


So we have decided to intervene, settle your brood fish into a suitable area for at least a day, prepare your hormone the day before and store in the fridge


I use CPE injections and get this in the form of a vial full of pituitary glands,( these are very expensive) every gland represents a fish. I grind these up in a small test tube with a small amount of sterile water or saline and leave over night, I use one large gland and one smaller gland for every 1 kg of body weight


The next day these are injected IP through at least an 18g syringe and the carp released back into the holding tank, In my experience the fish are ready 18 hours later you can check this by catching a female fish and just brushing the fish down its flank if the koi is ready, spawn will eject from the vent area ( dark brown in colour)


At this point, if you have spawning ropes in situ, you can leave them to do what comes natural and remove them after they have spawned or you can manually strip the milt and roe from the fish.


To strip the fish you need to first prepare a bowl of anaesthetic as the fish need to be immobilised while they are dried and stripped


In both cases with male and female the milt and roe must be stripped without any water coming in contact with them and that includes any droplets off the fish other wise the process will begin before you are ready


Get two clean bowls ready one for the milt and one for the roe do not mix at this point


I start with the female, once anaesthetised take the fish from the bowl and dry it off very carefully taking care not to remove the cuticle. (I use a towel damped with pond water and squeezed dry so itís just damp)

Once dry support the fish so the vent is over one of the bowls with your thumb and forefinger rub ventrally down the flank of the koi from the ventral fin area to just beyond the vent; the eggs will be displaced into the bowl very easily. (You may need an extra pair of hands with this)


Again warning: do not apply pressure as this can result in killing the fish, if the spawn is ready to come it will be ejected as you move the fish around so force is not required or desired


When the spawn has finished coming out, and again do not try to get the last little bits out or you will damage the fish and be there all day, return the fish for recovery to the tank ( apply plenty of oxygen) and put the spawn to one side.


Repeat this process with the male or males usually one or two males will be enough.


Again take care not to contaminate the newly yielded product with water.


Now we come to the mixing.


For this we need a strong bird feather around 8Ē long a fertilisation fluid and a strong arm because you are going to be here for a while so get yourself prepared with a radio and or your cigars or what ever you need to distract yourself with while the mundane mixing goes on


The fertilization fluid is a mixture of common urea, salt and water, if your going to hatch these fish in a zugar jar, you will also need a separate preparation of tannic acid and water


Dose rates for both at the end


So we have spawn and eggs separate and they are both inactive as yet, we pour the sperm/milt into the eggs and do a paramilitary mix with the feather ensuring the sperm is well distributed


We now have the two mixed together but still inactive. We now apply some of the fertilization fluid the urea/salt and water. About Ĺ a litre or pint .


This does two things, 1, the water element triggers the process to start. The urea and salt slows the whole process down and cleans the eggs. We now have up to 2 hours for fertilization to take place this enables a much higher percentage of eggs to become viable and therefore a higher hatch rate

In other words it stops the entrance to the eggs closing quite so fast and extends the life of the sperm.


If you want to freeze some sperm this should be done before itís mixed with the eggs and before itís activated with water.


As you begin stirring the egg mixture with the fluid, a scum will come to the top; pour or spoon this scum off after 10 or 15 minutes and replace with more fluid and continue to stir.

Repeat this process over the next 90 minutes ensuring the eggs are clean and all separated instead of stuck together but save some of this fluid for after the next process. Stir with feather every 10 minutes


Drain off the fluid and add the tannic acid into the eggs, this gets rid of the stickiness of the eggs do not leave this in to long, a few seconds at most and rinse through with some more fertilization fluid


Your eggs are ready to go for incubation now


You may want to use a zugar jar, a conical glass or plastic jar suspended over a tank. A pump is set up with a little air to bubble up at a few litres a minute of tank water via a small pump, this keeps the eggs in suspension, you will have to balance the flow through the jar as you want to keep the eggs in the jar and not have them spill over into the tank, kind of like a fluidised bed filter system


Once this is done the eggs are left to bubble away for the duration of the incubation

The fish, once hatched, will swim to the top and spill over into the tank below and you should be left with hatched empty shells in the jar


Other wise you can put the lot into a tank aerate well Ďtill hatched but then you have the separation problem after they hatch


Important: which ever incubation method you choose, dose the eggs with malachite green or Methylene blue on the second day of incubation but do not apply once the tails of the fish are emerging.


Fertilization fluid: 30 gm urea, 40 gm salt , 10 litres water

Cleaner: 0.75 gm tannic acid, 5 litres water. Apply to eggs for 3-5 seconds


Coming soon: raising newly hatched fry




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