The name Koi (KOI) started to be used in the betta fish market in Thailand, the home of betta fish, about 5 to 6 years ago.
In the early days, Koi-Color Short Tail Betta was given to individuals whose colors were reminiscent of Nishikigoi, a type of fish called marble.
At this point, the Koi betta had not yet been established in its systematics, and it seems that it just happened to appear among the breeding of Marble.
Japanese Nishikigoi are very popular and well known in Thailand as well. For this reason, Koi betta has also become increasingly popular in Thailand and is attracting attention. As its popularity increased, so did its demand, and breeders seemed to have made efforts to increase the rate of color retention.

For several years now, there has been an increase in the number of specimens exhibited at the Bangkok Beta Contest that have irregular red patterns on their flesh-colored bases, such as Ultraman (old!!). It is thought that the fish around here became the origin of the modern carp betta. After that, Koibeta evolved further, and the color became fixed with red and black patterns on a white background based on skin color, and large numbers were released on the market.
Looking at recent carp bettas, there are many individuals whose gill cover colors are transparent, and it seems that there are many strains of brushing (transparent scales), which is what we call tropical fish.

It has transformed into Koibeta, which has a color more similar to that of Nishikigoi, but due to its original marble lineage, no two individuals have the same color pattern.
From among the many fish that have been bred, the fish must be selected to select the fish with the color that can be called Koi betta, which requires a lot of effort and waste. Therefore, it is inevitable that it was traded at a relatively high price even among plastic cuts.
In the Japanese aquarium fish market, the popularity of carp betta has suddenly increased since the fall of 2014. The reason for this seems to have been a small feature on Koi betta in Aqualife magazine. It is very gratifying to see that Japan's ornamental fish industry, which has been in a slump recently, is being revitalized by the influence of magazines.
It seems like a situation like this hasn't happened in a long time, but I would like magazines to provide more articles that have a positive impact on the industry. 
In 2015, a new species, the Half Moon, appeared in the world of Koi Betta, which used to be limited to the Plakat (Short Tail Betta). Improving the popular Koi Betta into a Half Moon is something every breeder thinks about. However, it is not something that anyone can do unless they have a thorough understanding of genetic information and breeding techniques, and it appears that only a very small number of breeders in Thailand were able to succeed.

As of February 2015, according to the information I have obtained, only two breeders are producing Koi Beta Halfmoon.
Even at the Sunday Market, where there are many betta shops in Thailand, as far as I know, only two shops still sell Koi Betta Halfmoon.

According to a betta fish expert in Thailand, Koi Betta Halfmoon is produced in reasonable numbers, but there are still very few individuals with a tail opening of 180 degrees or more that can be called a halfmoon, and many of the fish that have bred are deltatail or superfish. Apparently it's Delta.
It seems to be quite a difficult task to select the truly high-grade fish from among them.
Moreover, because the temperature in Thailand is low from December to January, and the growth rate is slow, it will take about two more months before sufficient numbers can be put on the market.

In terms of the Japanese market, solid movement will be better after April when it gets warmer, so it can be said to be a good timing.
Under these circumstances, a friend of mine prepared a high-grade Japanese carp betta and half moon fish for the photoshoot, one of the few fish that are still on the market.
I would like you to see the beautiful colors and shapes.