Cecil, Bill and Dave have lots more experience than I have so take these ideas for what they are costing you.
The very first day the ice went out of our lake a little bit, I was catching LMB on crank baits. The water couldn't ever have been too much colder and I was using a pretty fast retrieve.
When I stock walleye, I think that they have to be at least 14-15 inches long to survive bass and catfish predation. These are eating size fish to most people. One other thing, we have tremendous predation on smaller fish. Walleyes have to be at least this size to compete for the next size up of forage.