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Koi Varieties - Black Zeus and Black Diamond

In today’s blog post, we are looking at some really interesting and special new koi that have been in development at Dainichi koi farm in Japan. These are called Black Zeus and Black Diamond koi and have only just begun to be introduced to the koi hobby with the first koi being imported into the UK only in late 2022. These varieties are certainly ones to keep an eye on!

These two varieties have been developed from two well-known but fairly new koi varieties, Kumonryu and Matsukawabake. They were developed at the same time, using similar starting koi and breeding for similar results but The Black Zeus variety was developed as a Gin Rin Aragoke Kumonryu and the Black Diamond was developed as a Gin Rin Aragoke Matsukawabake. Below, we will break down what all these words mean and what you can actually expect a Black Zeus or Black Diamond koi to look like:

Matsukawabake and Kumonryu

The Kumonryu and Matsukawabake koi varieties which are white coloured koi with a black pattern that constantly changes over the koi’s lifetime. Both Kikokuryu and Kumonryu koi are non-metallic varieties but the Kumonryu is also a Doitsu (scaleless) variety. Sometimes the Kumonryu will have a single line of larger scales down the dorsal fin, sometimes it will be fully scaleless. Both of these varieties are incredibly popular due to their changing black pattern, called Henka Sumi (HENH-kar SOO-me), as you never really know what the koi will end up looking like! Most koi with Henka Sumi will have a light phase where they are a mostly white koi, and a dark phase where they are mostly covered with the dark pattern and will gradually change between the two phases. Others will not change quite so much but no Henka Sumi koi will stay exactly the same over its whole life. It certainly makes for an interesting koi to watch!

Gin Rin

The term Gin Rin (GEEN-leen) is translated as ‘golden-silver reflective scales’ and is used to describe koi with beautiful, sparkling scales that appear to be of either a gold or silver colour. These scales give the koi a lovely, glittery effect and look stunning at all times, but especially so on particularly sunny days.

The Gin Rin variety was created by a very respected breeder called Eizaburo Hoshino in the early 20th century. The story that has been passed down over the last 100 years or so is that Hoshino came across a local fisherman who had caught a Magoi fish (a Japanese common carp, a black fish from which all modern koi descend) whose scales glittered and shimmered magnificently. Hoshino brought this fish and bred it with some of his own koi to eventually create the first proper Gin Rin koi. The scale type took a long time and a lot of work by various breeders throughout Japan to be fully stabilised but by the 1950s, the Gin Rin type was fully established and stabilised.


Aragoke (ah-RAH-go-KEH) koi are a new subvariety of Doitsu koi that have much larger and irregular scales than the typical Doitsu koi. The scales on Aragoke koi have been produced from Doitsu koi for decades but koi breeders always eliminated these koi from their Pongoi koi as they were considered to be poor quality. Recently, however, Mr. Ikarashi of Ikarashi koi farm challenged this idea and decided to grow on some of these fish rather than removing them. This resulted in the first Aragoke koi being shown to the public with mixed results. Some koi keepers loved them and some koi keepers disliked them but there was enough interest that more koi farms decided to also grow on their Aragoke and some more and more are appearing in koi keeper’s ponds.

The word ‘Ara’ comes from the Japanese word ‘Arai’ which means rough or crude and the word ‘Goke’ comes from the Japanese word ‘Uroko’ meaning scale. So, the name Aragoke literally translates as rough and uneven scales. Part of the appeal of this koi is the unevenness of the scales as well as their size so it is much less important than a regular Doitsu koi that the scales be neat and consistent – in many cases what makes a good Doitsu koi makes a bad Aragoke koi!


So, by combining all of these together, we can conclude that the Black Zeus koi is a white-coloured koi with a constantly changing black pattern over the white base colour. The koi also has large armour-like scales over its whole body and each of these scales have a beautiful, sparkling mirror effect. Overall, a very striking koi!

The Black Diamond is very similar to the Black Zeus, the difference being visible in the scales. In fact, the only difference between the two varieties visually is that the Black Zeus has Aragoke scales that were developed from a scaleless variety so the Aragoke scales are larger and more consistent. Alternatively, the Black Diamond has Aragoke scales that were developed from a fully scaled variety which has resulted in the Aragoke scales being generally smaller and less consistent as they usually appear mixed with normal-sized scales. In some cases, the scales on a Black Diamond look very similar to a normal, fully scaled koi, just a little bit larger.

These two koi varieties are definitely ones to keep an eye on. Dainichi have certainly developed some very interesting koi here!

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