05. Growing koi fry, harvesting and selling koi.

Last month we had successfully spawned our koi and hatched out their eggs to produce a hatchery full of fry. These have now been stocked out into our live-food-rich mud ponds. It’s June and we’ve got to get our koi fry as large as possible by September so they will overwinter well. As we don’t have the capacity to overwinter our 2-3” koi inside, they will be overwintered in their mud ponds.


The broodstock have learnt their keep for another year and it is imperative that we continue to protect and pamper some of our business’ most valuable assets. The best place for these workhorses is back in their dedicated mud pond. Any bruises, bumps or decline in general condition will soon be remedied in these unsurpassed conditions. I have never had to treat broodfish or worry about the health or wellbeing of broodfish when they are kept in a mud pond.

I cannot say the same thing when they are kept in intensive koi-pond-style recirculation systems. Once returned to their own outdoor pond, they will benefit from the natural environment and the females will lay down their eggs for next year’s spawn. It is vital that they benefit from the best food, supplementing their natural diet with a high protein premium koi food. The broodstock will spend all summer and autumn in their pond until they are netted again in February next year, ready to be segregated and manipulated.

Koi Fry.

After their first few weeks in the nursery ponds, the fry’s diet should also be supplemented with a powdered dry food. This is because the fry will have consumed most of the live food that the pond initially provided and it is a race to try and progress the growing fry onto a small floating pellet as soon as possible. Their dry supplementary diet is a high protein koi food ground down to different particle sizes using an industrial coffee grinder. The small fry start off with ‘espresso’ and move onto a coarse ‘cafetiere’ grind until they take a mini floating pellet after which their growth rate will rocket again. The ground dry food is offered via automatic clockwork belt feeders that are topped up each day. Each nursery pond will have 2 or 3 strategically placed feeders to try and reduce the inevitable competitive stress that the fry will experience when feeding under the confines of a belt feeder. Great care and judgement should also be taken with the quantity of dry food offered to these inch-long koi. Too much and they will eat until they literally burst. So fragile are these koi at this stage that the expansion of food in their gut can exert so much pressure that they will literally ‘unzip’ along the length of their abdomen. When this happens to thousands of baby koi, besides it not being a pleasant sight, it can seriously affect next year’s income (as well as the koi farmer’s morale).

As soon as these baby koi are large enough to take a small pellet, feeding is much more straight forward. The food can be scattered more easily and as it floats until eaten, you can easily guard against over feeding. Hopefully, your koi will have reached 2-3” by September. A nursery pond 10m x 40m would be expected to produce 10,000 2-3” koi from an initial stocking of 50,000 2 week-old fry.


We now encounter a major logistical problem in the koi farming calendar. Our koi will not grow from now (September) until March next year, so during this period they will not gain in value yet are vulnerable to disease and death and in pure business terms are a considerable risk ( i.e. they have not yet been converted to cash). Add to that the fact that the nursery ponds in which they are currently being held must be drained, dried, disinfected, fertilised and rotivated by April and ready for next year’s fry and you can see that we have a timing issue. Furthermore, the market for these fish is virtually non-existent until March next year when koi dealers and garden centres will want delivery (in anticipation of the Easter rush). So what can you do to solve the problem?

Having faced this problem I can appreciate why the koi farmers in Niigata look to sell their koi as early as October. This immediately frees up their space and instantly converts their koi into cash. This is hardly an option for the UK koi farmer who has to resign to overwintering his stock outside, selling them on as soon as he can next spring hoping that this leaves him sufficient time to prepare those same nursery ponds for that year’s spawn.

One of the benefits of farming ghost-koi (metallic koi x wild carp) is that the angling trade does have a large demand for fish in the autumn. This is an ideal route for moving large quantities of fish in one go – but at anything up to 10% of the price you would get for the same fish selling into the ornamental market. Bear in mind that the ornamental market will buy in much smaller quantities. Selling higher grade koi to the angling trade of course is not an option

The koi are harvested by:

1. Draining the pond down to 3’ deep.

2. Pulling a seine net through the pond several times until the catch each time declines to a small amount of koi

3. Drain the remainder of the pod completely and net the remainder from the catching pit at the deepest end of the pond.

4. Pick any remaining fish by hand from the muddy pond bottom

5. Once emptied of koi and water, the pond is then allowed to dry out, ready for this year’s fry in May.

Once we have harvested and graded our koi, we can hold them in outdoor recirculating systems prior to sale. We will have to take great care how we set the selling price as this will determine our overall profit (if we actually make one) as well as the speed at which we sell them. The grading procedure also provides us with the opportunity to select the koi to grow on for another year (assuming we have the pond space and finances to allow this luxury). The whole relentless koi farming cycle then starts again.

In conclusion, koi farming can be an excellent, highly enjoyable way of life. There are few things more rewarding than to see ponds full of beautiful (and valuable) koi that are there as a result of your own koi farming skills.

BUT. Having travelled through the koi farming calendar there are many risks and pitfalls along the way that can spell disaster at any stage. Koi farming exposes us to many other uncontrollable factors (such as SVC and more recently KHV) that could spell financial disaster overnight. So if your motivation behind becoming a koi farmer is to become a millionaire – then STOP.

I suggest you wait until you’ve either won the lottery, or find a willing financial backer to take the risk on your venture. The choice is yours!

Boxout: Some lessons learnt

1. Heating doesn’t always work. At my first experiences at koi farming, the hi-tech purpose-built koi farm had the capacity to heat its outdoor nursery ponds to 20C through the winter. The farm was situated adjacent to a landfill site which produced methane gas. This was burnt, producing several megawatts of waste heat. The water in the farm ponds was recirculated passed the heat exchanger to produce a field full of steaming ponds – Quite a sight in winter! Unfortunately, the way the ponds were heated meant that any live food that had been cultured in the ponds was quite literally cooked (and therefore killed) at the heat exchanger, giving the ponds a very clear and sterile appearance. This proved disastrous for raising fry – even if the water was 20C. Furthermore, the intention at this site was to grow koi through the winter courtesy of the waste heat. It was soon established that unless koi also experience a matching summer photoperiod they would not grow in the winter (even though the water was at summer temperatures and the koi consumed food at the normal rate). It has since been suggested that carp require a minimum of a 10 hour photoperiod to trigger the production or release of relevant growth hormones that convert food into fish tissue.

2. Be careful which koi varieties you choose to farm. Even though koi do not breed true, there are some varieties that are not as genetically complex than others, meaning that they are more likely to produce reliable results and a greater proportion of saleable stock. The most complex varieties are Kohaku, Sanke and particularly Showa. These produce patterned, recognisable offspring in very low numbers. However, Ogons (Purachina, Yamabuki etc) Shusui and of course Chagoi produce more reliable results, giving a greater proportion of saleable offspring. So it is worth buying broodstock from these varieties.

3. Try the metallic cross. A handy trick to increase the value of some of your stock is to cross any of the more complex varieties with a metallic koi. Such a cross generally produces a diverse mix of koi that may not be of recognisable varieties, but will still have general appeal to the mass ‘garden centre’ market. Furthermore, as all fish produced with this cross will show attractive metallic features, you will be able to market every fish; no culling required. This could not have been the case had it been a straightforward complex variety x complex variety cross.

Have you ever noticed that koi farming is the complete opposite to koi keeping?

1. Filtration? In a mud pond, there is no filtration. In fact, you will be hard put to find any typical koi pond hardware in a mud pond. The pond’s integral ecosystem is responsible for and more than capable of producing an environment that will boost the health, growth and colour of your koi better than any artificial koi pond.

2. Organic Matter? As koi farmers we add it, by the bucket load rather than remove it to enhance water clarity. It is the organic matter (chicken manure) that will kick start our mud ponds into action. Can you ever imagine what effect adding chicken manure to your own pond would have?

3. Water clarity? There is none. Our koi thrive in turbid, clay-rich conditions. These aquatic pigs literally thrive in mud, glorious mud!

4. Running costs? These are minimal. It will cost more to run a typical 3000 gallon koi pond than a 1 million gallon koi farm pond.

So why don’t we keep our koi in the conditions that are proven and shown to be unsurpassed for our koi? As koi keepers we are forced to make a compromise between what is best for our koi and what is best for ourselves. We try and make up for it by adding clay periodically and ensuring our food contains the colour enhancing algae (spirulina) that our koi would otherwise be benefiting from in a natural pond. But we often fail and we are forced to treat when things go wrong. I can honestly say I have never had to treat koi in a mud pond (but rather found a mud pond to be the best treatment for any sick or ailing koi).

Kill blanketweed and string algae.