This is nothing but a theory but I suspect that the softness comes from them being in a small body of water. No where to go so less swimming thus less building of muscle. Bigger open waters they are constantly on the move chasing bait and moving from deep to shallow water and such. In small ponds they just lay around and wait for bait to come to them plus I find fish a lot softer in warmer water. In the case of small waters they can’t escape warm water by going deeper.
Proud Member of Team Geezer
Charlie Weaver USN/ENC 1965-1979