Alarge-mouth bass is taken from a fresh water lake and transplanted into the river. if the conditions for survival are optimal, would you expect the cells in the fish to shrink, swell, or stay the same?

The cells will make some sort of reaction, there's no doubt about it. But for a bass I believe that their cells will stay the same or shrink over time.
Bass are strong fish and they usually do well when there's a change in conditions made in the environment. But it depends on what this river has in it and if it leads to bigger opened waters.
If there's a shortage of food sources for the bass it'll have to adapt quickly or it'll die from the predators in the area. If there isn't any places the Bass can lay their eggs (reproduce) its population will die in that river.
There also competition. In that river it could have socked eye salmon in it or catfish even pikes. So the Bass cells would stay the same.

Hope this helps