I would think at the 6 to 8" size they would be feed trained but I could be wrong about that. My 10" sized were feed trained. And it sounds like you need to thin out the lmb. The hsb can put a pretty good dent in your forage numbers and will grow pretty fast and can double in size each year for the first 2 or 3 yrs, if they have the food to eat, forage and pellets. I would advise thinning out the lmb and adding some type of forage fish that likes open water before I added the hsb. Where you are I would think Golden shiners might be the way to go for forage but I'm a southern guy so I could be wrong when it comes to the needed open water forage up where you are.
