Hadn't heard that but I can believe it. These 3" RES seem a lot more lethargic at current water temperatures (50-55) than the same size BG.
A week or so ago I dumped a batch of them in my main pond. Thought they were going to die as they rolled over and floated around. From then on I was much more careful about tempering them to the new water. In the case of my forage pond and main pond, they are 30 feet from each other. I figured temperature and water would be close enough no problem. Big problem. I suspect there is a pH difference as the forage pond is nearly entirely lined with limestone rock.
So from that point forward I was much more careful about tempering the water in the bucket to the new pond water and had no more problems.
But I can tell the RES swim away a lot more lethargically than what BG would. They are already cold.