I read an educational post on a social network by a gentleman named James Story, from Alabama. I asked him if I could share it here, and he was gracious enough to do so. He posted how he physically inspects his Koi in the spring and fall, and explains why. His post is below. I hope you find it helpful. Thank you James for sharing your Kio keeping to help others be better Koi keepers.
Health Checks: People often ask me why I catch my fish and do this. I believe it is important to look and feel them over. I do it twice a year, once before winter and once in early spring. There are lots of ailments that you cannot see just by looking at them in the pond. Here are the things I look for (I am sure I will learn more things to look for from more experienced keepers).
*Overall appearance of skin - free of redness, irritation, and visible parasites.
*Body - to see if it is symmetrical, straight spine (visually draw a line tail-dorsal-nose) with a soft belly and no growths.
*Skin and Scales - both should be smooth. A sandpaper feel to the sides can indicate flashing that you have not witnessed (but rough gill plates indicates that the Koi is a male). Make notes of blemishes or shimmies.
*Underside - I flip them over, you can get lesions and ulcers on the bottom of your fish and they can kill the Koi before you can see them from the top.
*Mouth and Eyes - make sure the mouth is functional and the lips open downward and that the mouth and eyes are symmetrical. They can get deformities to the mouth that may hinder eating. Since the mouth faces downward, you may not otherwise see this.
I have found that this allows me to study all these parts and better understand what judges and others are saying when they speak about quality. It also helps me know what to look for in future fish.
By knowing the detailed baseline condition of your fish, you can better judge if they are worsening or getting better. I am no pro, but wanting to share what I do and generate conversation.