rosies are a color morph of Pimephales promelas (a.k.a Fathead Minnow). They do like colder water, but can tolerate warm temperatures. You can't float them too long or they run out of oxygen, especially if there are more than 2 dozen in a smaller bag. I would also try to get them hand-feeding and only put one in at a time. If you need to float them for more than 10 minutes, put an airstone in the bag. You can also temper them by adding a small amount of warmer water at a time.
Rosies just aren't a very hardy fish to keep sometimes, even though in the wild, FHM can tolerate high temps and low oxygen.