shipping fish question ; safe how long?

[scuba dude]

I have a question on shipping/transporting fish and how long they will survive.

I was away on vacation and a LFS where I was had some Panda Garra cats that I have been looking for and unable to find in my area so I wanted to bring a couple home but the girl at the store insisted that they would not survive.
My plan was to pick them up at 6pm when the store closed for the evening and then travel home the next day first thing in the morning , total time that they would be in a bag was 18 hours tops. I was going to float the bag in a cooler with water the same temp as the fish water, they could have added O2 to the bag and some extra water as well. How is it that people here ship fish cross country but they would not survive 18 hours in a bag , inside a cooler with water to float the bag to maintain temperature?
Am I missing something here? How would any one else pack fish to ship??


Thanks for any input on this.