Robert,
Fish flavor can be effected by diet. Although I wouldn't expect this to be a problem with the quality food your feeding them, perhaps they are eating something else as well.
I have family that lives on a very slow moving body of water just below Tulloch lake and above the Stanislaus river in Jamestown, CA. In the spring when the spillway is flowing the fishing is great and bellies of the trout are filled with shad. These are some of the best tasting trout I have ever had. On the other hand, on the same body of water, in the summer time when the spillway has stopped and is no longer bringing in shad, the bellies of the trout are filled with snails and other invertebrates. Undoubtedly, they are foraging on the bottom due to lack of shad. These fish taste like dirt.
In my own pond (Pacific Ocean, Central Coast, CA) my favorite tasting fish are Cabezon. When you fillet a cabezon and its belly is full of crab, the fish meat tastes like crab. If there is no crab, it tastes like fish...good fish, but not crab.
Just goes to show, you are what you eat. Check out my Lingcod from my last outing.
