Bruce,
Pardon me for missing the point, but is the difference in size a function of the feeding behaviors of each individual fish in response to temperature (as implied in your last post) or the use of different types of pellets (as suggested in your original post).

A combination of both?

"Only after sorrow's hand has bowed your head will life become truly real to you; then you will acquire the noble spirituality which intensifies the reality of life. I go to an all-powerful God. Beyond that I have no knowledge--no fear--only faith."