Look at behavior first
A healthy koi should swim steadily, respond to its surroundings, and avoid gasping, clamped fins, or isolation. Behavior is not everything, but it is a useful first filter.
Body shape matters
Choose a koi with a smooth body line, balanced shoulders, and no visible bends or deformities. A beautiful pattern is less valuable if the body is weak.
Skin and color
Clear skin, even color, and a fresh surface impression are important. For patterned koi, step back and ask whether the overall balance still looks pleasing from a normal pond-viewing distance.
Ask the seller
- How long has the fish been in their care?
- Was it quarantined or observed before sale?
- What water temperature and food has it been used to?
- Can they show clear photos or video from above?