Frequently Asked Questions on Koi carp

How big do koi grow?

Koi carp can grow to 120cm in length, although any fish over 100cm is considered huge. Most koi don’t grow much over 60cm in length in average garden ponds and a number of factors affect growth including genetics, water temperature, food, space and water quality. If a fish didn’t have large parents and isn’t fed the best food, in year-round warm water, in a large pond, it may never grow to record size. Lots of people think their koi are large (Ghost koi grow big and quickly,) but if you go to a koi show and see a 90cm or even a 100cm Jumbo, you’ll be amazed at just how big that is.   

What are koi worth?

Any koi is only worth what someone will pay for it, but one Japanese show winning fish sold for £1.4 million pounds. Fish worth over £20,000 have been bought and imported to the UK but at that sort of money, it is all about bloodline, parentage, shape, skin quality, pattern, variety and the potential to be a Champion. All show winners are female as they grow larger than males (size is rewarded,) and the most expensive fish are always Go Sanke – one of three varieties including Kohaku, Sanke and Showa. Red and White Kohaku are the most desirable variety at the moment, winning shows in the UK, Europe and Japan. Ghost koi are crosses between koi carp and mirror carp and are rarely worth more than £100, regardless of size. If a fish is big it may not be worth much either as value is related to the pattern, body shape and bloodline.  

What do koi eat?

In the wild carp are omnivores, eating everything from worms and snails to mosquito larvae, plant matter and detritus. They eat from the top, middle and bottom water layers, slurping food from the surface or sifting muddy substrates for juicy morsels. Anglers will know Koi will eat anything from Sweet Corn to Spam, to maggots and Boilies. 

In captivity, Koi are fed floating food sticks and pellets almost exclusively. Different diets are available for different times of the year and water temperatures, with low protein Wheat Germ being fed in cold weather, and high protein growth and colour foods being fed in summer months. If you want great koi don’t skimp on good food, as good ingredients don’t come cheap. For maximum growth potential load up an Automatic fish feeder to feed your fish several times a day when you’re not there. 

How do you breed koi?

Koi carp are egg scatterers with slimmer, smaller males chasing the larger females before pushing them into weeds and expelling thousands of eggs and sperm together. Do nothing in a large planted pond and your koi may spawn of their own accord when the water warms in spring and summer. They eat their own eggs after spawning so wait to see if a few survive or remove the plants they spawned on and raise separately. 

If you want to deliberately breed koi, separate a ripe female and two males and move them to a spawning vat containing only water, an airstone, and koi spawning brushes. On a sunny morning if the temperature is right they will spawn before the parents are placed back in the main pond and the eggs and fry are raised separately. 

Professional breeders may even hand strip selected males and females, squeezing the fish’s flanks by hand and mixing eggs and sperm in a bowl. Fry can be placed in a growing pond consisting of green water and live Daphnia or raised on newly hatched Artemia. Young koi on sale have all been through the culling process whereby only the fastest growing fry with the best patterns are selected. A high-quality fish may literally be one in a million. 

What size pond do koi need?

Most Japanese koi owners aim for a pond of 5000 gallons (22,700 litres) or about 15’x10’x5’ 5mx3mx1.5m. Depth is important for overwintering and developing good body depth. Too small a pond and your koi will stunt. It is true that Koi will only grow to the size of the pond as they release growth inhibiting hormones when overcrowded. Understock and change lots of water in order to facilitate growth. 

Do koi eat plants?

Yes, koi can and do eat plants, and in plant-free ponds, some koi keepers feed their fish on whole lettuces to provide some roughage. In the main pond plants can be damaged by koi as they root in and around them in their search for aquatic invertebrates. Some koi will eat all the plants that are placed with them while in other ponds they won’t eat any. This could be down to a number of factors including not getting enough food or being dietary deficient. But most of the times when water lilies don’t do well with koi its because the delicate shoots are damaged early in the season and the rhizomes are dug at and exposed. A mature, potted lily with large floating leaves and soil protected by a deep layer of large stones is usually ok with most koi. Usually! 

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Jeremy Gay is an author and freelance aquatic specialist. A former editor of Practical Fishkeeping magazine, he offers a wealth of experience on all things aquarium and pond.


Comments

  • Avatar Alan Epsom Posted 24/02/2020 at 4:45 pm | Permalink | Reply

    I was brought up with looking after fish I even belong to a fish club went to many shows won a few trophies on the way I still keep fish I have a big pond in my front garden and one in the back and a tank I do think koi are a nice fish but I think gold fish are just as nice I do I joy watch the koi carp on Facebook

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