I don't think having to cover the concrete totally would be necessary. If you want fish to spawn in the pond, you could provide an area for them (at the proper depth and of the proper substrate) for them to spawn on.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).