First of all, there is absolutely no substitute for practice. By that I mean look at as many Koi as you possibly can, even if you have no intention of buying. Study them, compare them, discuss them with the dealer and try to find out what he looks for when he buys his stocks of Koi
It is sometimes easy to form the opinion that a fancy price tag will mean a better fish. That is not always the case. For instance, a dealer may label a particular Koi as ‘Tategoi' (a Japanese word that means a Koi with the potential to improve), in order to realise more profit on the sale. This label does not guarantee that the Koi will develop for the better in years to come. Other fish may display really vivid coloration and be priced accordingly, yet after only a short time in your pond will begin to lose their colouring.
The same arguments can be applied to Koi from well-known Japanese breeders. Just because the fish is said to come the Kawasaki Koi Farm does not mean that it does, or make it a better fish than you see before you. That may sound a little obvious, but claims can be made that certain blood lines develop desirable characteristics in years to come, and to a large extent that is true, but it is not guaranteed either.
If you are looking to buy a high grade Koi, whether it be for showing or just to improve the stock in your pond, you will almost certainly be paying a lot of money for a Koi with a recognised ‘pedigree' bloodline, and very likely it will be labelled as ‘Tategoi'.
If however, like many hobbyists, these things mean little to you, what should you be looking for in a new Koi?
Surely the two most important considerations are
1) Do you like it?
2) Is it healthy?
The first point sounds a little obvious, if you didn't like a particular Koi; you probably wouldn't buy it. Don't be swayed by other people's opinions on pattern and which variety it is. You are the best judge of what fish to have in your pond. If YOU like it, then it's a good fish. It will pay you to compare your intended purchase with one or two other Koi; you may find a better one you hadn't considered.
It doesn't matter what anybody else thinks until you start to consider what I would call the technical merits of Koi. By this I mean things like body shape, skin quality, and future development and so on. These points become very important if you are buying a Koi with a view to exhibiting at shows.
The second point is possibly a little more difficult to grasp, and is sometimes overlooked in the heat of the purchasing moment.
Most Koi keepers are aware of the golden rule of quarantining all new purchases. This is fine, but not everybody has the opportunity or desire to have a second pond. So it is even more important to be as sure as possible that any new Koi bought are in tip-top condition.
So what are the main things to look for? There are a few things that are easily picked up such as split or missing fins, bodily injuries, perhaps the Koi isn't swimming properly, or its body may be deformed. Relatively minor things like split fins can heal very easily most of the time; other more serious defects should be avoided. Do not listen to dealers' stories such as ‘It's had a hard journey from Japan, it'll be ok in a couple of days', or ‘It's been treated and it will be fine'. If it's going to be fine you can go back in a week or two and see for yourself. If it's not there, why worry, there are plenty more Koi where that came from.
There are things that are very difficult to pick up in a short time and subsequently develop into more serious problems, things such as internal injuries or infections. This is the reason to buy your fish from a reputable dealer who will be considerate when you tell him that you have had problems with fish bought at his premises. Of course, if you keep losing fish, then perhaps you should examine the way you keep them.
So, you've found a fish you like, it appears to be in good health, and it's within your budget. Don't be in a rush to secure the deal. Take a while to study the Koi, as I said earlier, compare it with one or two different Koi, the dealer will be happy to show you some more fish. If he isn't, you are probably in the wrong shop, and maybe he's in the wrong business!!

Happy hunting!

Steve Brown