What would cause Koi to slowly become deformed until they almost resembled a Z?

Question

looking down from above them and as a result could only spin around in circles

Answer 1

Here are some reasons a fish may develop a bent spine.

If born that way, the fish may have a genetic abnormality.

If born that way, the fish may have incurred a developmental problem while growing inside the egg. This could be related to diseases, temperature, injury, etc.

If the fish was shocked via a faulty heater, pump, etc. or via lighting (striking a pond or surging through a house), this can result in a bent spine.

A severe injury can bend the spine. Normally though if broken, the fish would die right away.

Fish tuberculosis sometimes results in a gradual development of the curvature of the spine. A fish with this condition (fish tuberculosis with a bent spine) is often also anorexic.

Certain vitamin deficiences can result in spine curvature.

It seems that many fish nearing the ends of their lives get bent spines which usually match one of the above problems but sometimes do not.

Answer 2

It's a shame, another Koi on drugs.

Answer 3

there's really no way of knowing, a friend said he thought it was from pond being struck by lightning, i think it could be from being handled or netted roughly, they probably have diseases and birth defects just like humans and other animals

Answer 4

Are your fish inbred? Usually inbreed fish have curved spines and other deformed features