The Bluegill are getting a bad rap here.
I understand the problem, nipping of people, not sure it's the Bluegill that are guilty here though.
It's more likely the Hybrid-bluegill, and more importantly their offspring - the Green-sunfish, that is mistaken for Bluegill.
The man made Hybrid-bluegill are 1/2 Bluegill, 1/2 Green sunfish, their offspring are, all Green-sunfish. Those are the nippers.
Stay away from the Hybrids, if you want an enjoyable swimming pond.
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