Experienced koi breeders, with knowledge of the parent fish lineage, can often detect differences in body conformation even at the small tosai (first-year) stage or during the initial culling of fry. For seasoned koi enthusiasts, a reasonable assessment of body shape may be possible when the koi reaches about 35–40 cm in length. For most general hobbyists, a basic judgment of body conformation is typically not reliable until the koi grows to at least 55–60 cm.
Judging a koi's body shape relies heavily on understanding its bloodline and accumulating practical experience. A key part of this assessment is distinguishing whether the koi truly has good body structure or is simply carrying excess weight (overfed).
