Its an equation. Oxygen in water (concentration and volume) and use by the fish (respiration). Less fish + cooler temps + less time = better survival. More fish + warmer temps + longer time = poor survival. I have had good luck with bagged fish put in an oxygen-charged bag during early spring with a two hour trip (minimal losses). The hatchery that I used leaves a certain headspace to be sure the O2 lasts. I have also had fish delivered from a hatcher quite a ways off with excellent survival. I assume they aerate the water constantly.
