Hey, I just stopped at petsmart this morning ( a local chain out here, a lot like Petco ) to buy some frozen brine for my tropicals and marines. And they had an Impressive selection of very low quality koi! In truth, many were what I would call colored carp more than koi ( which I tend to think of as nishikigoi). Of all of them, and I've observed and mentioned this before, the best representatives of a known variety were - Bekko & longfin purachina ( but for the deformed faces that were turned under).
At any rate, I have to say the water looked good ( not cloudy or organically a mess). And the fish were in very good condition/health. The longfins cost more than the 'koi'. $4 - $14.
I tried to imagine if I bought the entire stock, if I could hope to learn anything? I found I was dividing the patterned fish from the solid fish, and except for the bekko, the rest were on the verge of 'failure' at only 5- 7 inches and in a juvenile stage of development. The bekko looked like a few would have a shot at deeper surface sumi and had the very classic whiter skin that both bekko and Goromo are typically born with. but the skin was wrong- bright hard white and very thin density ( but they WERE young).
If you go to the big wholesalers of koi and longfins in the tropical fish trade- the koi there, mostly come from the South of the USA, Taiwan, Thailand, Korea, China. These are mass production countries/facilities- very professional in some cases but of the group, only the Taiwanese and Koreans have much of a handle on gosanke. I have gone and scraped this stock at the import facilities and I have to say, they are mostly clear except for the fish coming up from the south of our own country. In those I have found the 'hat trick'- trichodina, ich, costia on a regular basis- the slides are quite impressive in both numbers and varieties!
As for deformities, the rate is very high and you can see them well when the fish are in aquariums ( better than from above, this is why it is a good ideas to examine all purchases in the bag by holding it up to the light). The longfins today all had fin deformities. I'd say about 10% of the koi had head and/or mouth deformities.
It was a very interesting experience. I can't say I learned anything or that by raising these fish I would learn anything. But I did have some opinions re-enforced.

JR