overnight delivery for sure. fast the fish for 2 days before shipping. depending on the fish size and quantity 1/4 water and 3/4 air give or take. double inverted bagged. heat or cold packs as needed. put the bags and heat or cold packs inside a styrofoam container. put the styrofoam container in a cardboard box. maybe use a 1/4 of a bag buddy tablet or so.
I use styrofoam to line the box for insulation and padding. Then the styrfoam is lined with bubble wrap. Fish are double bagged with no corners and ammo lock, using fresh water. Like someone said they arent fed for 24 hours befor shipped.
After they are bagged they are labeled and then wraped in polyester fiber and then wrapped with bubble wrap. Throw in a crap load of packing peanuts, put the styrfoam lid on. I then add care sheets and acclimation guides to the box along with any gifts or extras and tape a heatpack to the lid and seal the box. Most people will want USPS priority, just dont offer a live arrival guarantee unles it is Overnight Express. If you can convinve people UPS is so much better than USPS.
Also, its up to you wether or not you mark LIVE FISH on the box, I have had some crazy times at the post office trying to ship them when labeled like that instead of just fragile. Spent hours before showing them their terms with no luck, but im not telling you not to label them properly or anything like that
Anymore questions or anything I missed please ask.