Why ?

[Rutilus Eye]

With Koi in a garden pond it is invariably a parasite problem that causes it. These are microscopic or very small parasites (not fish lice or leeches) and it occurs mainly in spring when the Koi's self defence/immunity is still low whereas the warmer water is ideal for the parasites.

Having said all that lot, real carp go about it any time of the year. We used to call them "Bennys" for reasons that are now lost in the mists of time..

[Julian]

The best explanation I have heard fo why carp leap out of the water is: because they can _ they just enjoy doing it.