03. How to farm koi

By now you will have spent many thousands of pounds on constructing and developing your new koi farm and hatchery, and already the clock is ticking on the time by which you need to see a return on your investment. As we will see, although you are now in a ‘production’ industry, you are dealing with living organisms and there are certain things that cannot be speeded up – no matter how impatient your financial backer or your bank manager may become. The koi set the pace for this investment. Having said that, there are one or two areas in which you can save time over nature’s preferred pace – and we’ll be looking at those in this article.

We’ll be looking at how to farm koi in two parts. In this first part, we turn our attention to preparing everything on the farm for the spawning event. In part 2, we look at spawning, raising, marketing and selling your koi.

Koi farming has been compared to pond filtration. Firstly, because you can use several different methods to achieve the same successful results and secondly, different people will tell you that their method is the best! Please bear in mind that although the methods I describe here are used across the world, but are not the only way to farm koi. The reason why I’m sharing these particular methods with you now is because these have worked for me repeatedly and predictably.

Several assumptions.

Now that we are about to look at the ‘nuts and bolts’ of koi farming, I am making 3 assumptions:

a. We are using a semi-intensive method of farming koi

b. We are farming koi in a temperate (UK) climate

c. Our outdoor pond growing season runs from March to September.

Preparation = Success

In order to be successful koi farmers, we need to prepare three things before we can spawn.

1. Broodstock

2. Hatchery

3. Mud Ponds

1. Preparing the Broodstock.

I find it useful to set the date on which I plan to spawn as soon as I can. Once set, it focuses all other farm activities and preparations towards that date. I generally set an early May spawning date. When teaching Fish Farming and Aquatics at Brooksby College, one of the first dates for the students’ diaries when they enrolled in September was to inform them that we’d be spawning at 10am on May 3rd. And as we will see, using the appropriate advanced techniques we can be this precise. Once you have set the date for spawning, you will notice that the preparations made for the broodstock actually revolve entirely around the females’ requirements.

July – September (preparing for a May 3rd spawn)

This period is of vital importance to next year’s production. This is the period when your female koi will be producing eggs that will ultimately lead to your fry next year. The more eggs your females produce, the greater the potential for good quality koi in large numbers. For this reason, your broodstock should be given the best quality environment and diet which is effectively a well-fertilised, nutrient-rich mud pond with supplementary feeding (a high protein, dry diet). Special measures should be taken against predation and theft and provision for additional aeration should be made in the warmer weather. In return, your faithful female broodstock will create and store next year’s eggs in abundance.

October – January.

The broodstock remain outside during this period and their activity and appetite will decline with the ambient temperature. The broodstock pond will be at least 4’ deep to ensure your koi’s safety. You may be questioning why the farm’s most valuable assets are being put at risk outside, at the mercy of the British winter weather. Experience has shown that breeding stock benefit from experiencing a ‘freeze’ for 3-4 weeks. This also helps the koi farmer as it draws a line between last year and the year to come in terms of the koi’s biological clock – effectively re-setting it at zero. It is essential that you know your females’ clocks are set to zero as this will tell you how and when you need to manipulate them to get a predictable response.

February – April

The final leg of the journey to spawning starts here. Your female koi will have ovaries full of immature eggs and it is down to you to help your females mature these eggs and then release and fertilise them to produce this year’s fry. The objective between now and spawning is to mature the eggs faster than they would mature if the females were left outside, at ambient temperatures. This means that you can then spawn earlier, and provide your fry with a longer growing period outside. This will produce larger, more valuable first year koi, and also give them a better survival rate through their first winter.

Broodstock manipulation.

In order to have complete control over your broodstock, you need to have an indoor facility which for convenience will be adjacent to your hatchery. The broodstock will be brought inside into their own maturation system. This consists of two large indoor ponds, one for each sex, ideally sharing a common filter system. This means that as they approach their spawning period, they are able to gain full benefit from any inter-sex pheromonal interaction, leading to a more predictable spawn. The broodstock are sexed, with any whose sex you are unsure about going into the males’ pond. (If you mistakenly put a male in the females’ pond, you could stimulate all of you females to flock spawn with that single male, leaving you with no eggs for this year!).

The next time the males will mix with the females will be in June, when they are returned to their outdoor broodstock mud pond. The sexes are separated to prevent an uncontrolled, spontaneous flock spawn.

Once the broodstock have been inside and accumulated to their new ponds, the water temperature is raised from 8C up to 15C over the next couple of weeks. Experience again has shown that females will mature their eggs and be ready to spawn having experienced 1000oD (Degree Days).

What is a degree day?

A degree day can be calculated as:

No. of days x average daily temperature in C

Any days that do not reach 15C do not count towards the accumulating degree days. So for example, 5 days @ an average temperature of 16C = 80 oD. 18 days @ an average of 10C = 180 oD, but as the temperature was less than 15C, we don’t count these days. As the temperature is soon raised to 15C when the koi are brought inside, very few days are not counted towards the approaching 1000 oD target. A log is kept as to how many degree days have accumulated and when the magic figure of 1000 has been reached, the females will be in a mature state, ready to spawn. So from March to April, the broodstock ponds are raised to 18C, which takes approximately 2 months to reach 1000 degree days.

Light to suit.

The females also use photoperiod (daylength) as a cue to what time of year it is, so an artificial daylength of 16 hours is created each day using artificial lighting on a timer. This reinforces the effect that the rising water temperature is having on the koi’s physiology, by delivering an artificial ‘summer’ daylength and water temperature in March.

What about the males?

Have you noticed that we’ve not paid much attention to the males yet? That’s because they produce sperm reliably and as long as they enjoy a good, warm environment and a good diet, they will perform as desired with minimal notice (sound familiar?). As the degree days start to approach 1000, the females will start to swell around their abdomen as the eggs mature. This will be the first indication as to which females are likely to spawn, allowing you to make provisional pairing plans – ready to cross the eggs from specific koi with the sperm of others.

This period will also indicate which of your females deposited eggs last year while in their mud pond. If any of your females did not deposit eggs (for any reason), then they will not swell up like other ripening females and they will not spawn this year, no matter what you try and do.

2. Preparing the hatchery.

The hatchery consists of any number of independently filtered (to reduce risk – not wanting to put all your eggs in one basket) recirculation systems. The hatchery tanks (typically a 2m2 free standing tank) will be the site for the first 2-3 weeks of your fry’s life. Your hatchery systems should use belt-and-braces filtration as they will experience incredibly high organic loads from a standing start. If their biofiltration capacity is lacking, then the development of your koi eggs and fry will be at risk. Because disease can also be a real threat, fish should not be used to mature these systems for the fragile eggs and fry so the regular loading with ammonium sulphate weeks prior to the spawn should be sufficient to mature the filters.

Other things to prepare and check include:

1. Central mesh screens are clean and well sealed. These will retain the fry within the tanks, but allow water to pass through and circulate through the pump and filter.

2. Pumps. For the next 2-3 weeks your whole year’s production is very vulnerable, at the mercy of pump failure. Check that all pumps are working well and running silently.

3. Prepare the mud ponds.

For those who are familiar with cooking a roast dinner, preparing a koi farm for a spawn is very similar. A joint of meat, roast potatoes and vegetables take different times to cook, but need to come to the table at the same time. To achieve this, the different parts to a meal are put in the oven at different times, with an eye on the time when the meal will be served. Koi farming is very similar. The preparation of the broodstock started last year, the hatchery a few weeks prior to the spawn and the mud ponds a few weeks later so that they are ready to accept the fry when they need to go outside. Just as the potatoes will burn if they are put in the oven too soon, the mud ponds can under perform if they are not prepared at the right time in relation to the spawn and the subsequent stocking out of fry.

The nursery mud ponds will rear the fry from 3 weeks old to their first year (3”+). Koi fry are raised in mud ponds using the ‘stew pond’ method.

Drain and dry the pond out from last year’s production until dry cracks appear on the clay pond bottom.

Rotivate and loosen up the pond bottom

Add lime (CaOH) to kill any residual pathogens and to buffer the pH

Add manure (pelletised poultry manure). Combine this with a faster-acting inorganic fertiliser (super phosphate / ammonium nitrate).

The manure and fertilisers are added to encourage green water which will be the vital element to feed the invertebrates on which your fry will gorge themselves.

Then fill each nursery pond simultaneously up to 12” depth. This should be started on the day of the spawn because the ponds will take approximately 3 weeks until they are ready to accept the fry. If the ponds are not filled at the same time they will be at different stages when the fry are stocked out – giving mixed results. Once your ponds have 12” of water (shallow enough to make them warm up in the sun), just let them ‘stew’.

14 days after filling, the fertiliser and good sunny weather (hopefully!) will turn the clear, fertilised water into a pea-green soup. This is dependent on the weather and either extremely sunny warm weather or cold and cloudy weather can dramatically affect the rate at which your pond ‘cooks’.

21 days after filling (and consequently after the spawn), daphnia and other small crustacea will appear and start to graze on the algae in huge numbers. When the daphnia density forms clouds, then that is the stage to stock out your fry.

28 days + after filling

Your fry should have multiplied many times in size in their first week in a mud pond, but if for any reason you have to delay stocking your ponds with your irreplaceable fry to 28 days after filling, then the daphnia will have been succeeded by carnivorous insect larvae such as dragon fly and great diving beetle larvae – which will predate upon your koi fry. You cannot afford financially to leave it this late to stock fry and you cannot also stock too early, before the daphnia are ready. Everything must come together at the same time, just like that roast dinner.

Kill blanketweed and string algae.