I'd seen these sort of nests in the Hosta Garden pond years ago, at the South Carolina Botanical Garden (where I taught and worked for many years). They were brim, there.
What sort of fish do colonial nests, and seemingly reuse them, I've not much clue.
I guess I need to consult my friend Google! (See update below)
|Fish "nesting" sites (Bass Pond, Biltmore Estate)|
An follow-up note: this post from the Lincoln Park Zoo describes the interesting nest-making and territorial behavior of male pumpkinseed, bass, and bluegills there (not to mention their parental role!)