If you have an outbreak of bushy pond weed like I do that covers a third of the pond, I bet they would not wipe out all the small prey fish. My gams are doing just fine with all that cover.
That is in my one acre RES/SMB pond. I have been putting in a couple dozen FHM about five days a week in also. If the pond were bare, it would probably be a waste of time. But with all the bushy pondweed hopefully enough of them will survive till spring and reproduce. I trap them out of my forage pond so it is not like I am having to buy the FHM.
