Culling in a pond?

[addy1]

I have plenty of plants for egg hiding, but those suckers are hungry and seem to wipe out most.
This is year 6 with fish, still have a lot of water room for more fish..................no koi

 

[Tula]

I have plenty of plants for egg hiding, but those suckers are hungry and seem to wipe out most.
This is year 6 with fish, still have a lot of water room for more fish..................no koi

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....and there is the problem....koi LOL Also my pond isn't very big!