I am not understanding the part about why you would want to put fish in a carbon dioxide compressed atmosphere. I would think that would kill the fish but I don't know much about that.

That said they do sell a device for making soda water with carbon dioxide in a soda bottle. You can also make one yourself with a schrader valve for a car.

I am not putting CO2 into the bottle!

Soft drink company can put compressed CO2 into the bottle and seal it. So can I put compressed air into the bottle!

But how? Anybody know an easy way?

Another advantage to the plastic bag method is that it's easy to float the bags in the target aquarium while the water temperatures slowly equalize (to avoid thermal shock) before gently releasing the fish.

I don't see any reason to compress the air; certainly not CO₂ unless you want dead fish. I'd use large gallon-sized bottles (or bigger; the biggest ones I could get and carry) and leave a large air space at the top so that oxygen can dissolve into the water as the fish breathe.

I'd actually leave the caps off if possible and use supports to keep the bottles from falling over. If that's not an option, I'd stop about half-way and pour some freshly oxygenated water into the bottles with the fish.

To oxygenate the water, just fill the bottle half full of water, cap it, then shake it thoroughly to dissolve air into the water.

To oxygenate the water, just fill the bottle half full of water, cap it, then shake it thoroughly to dissolve air into the water.
Just not with the fish inside I hope.

I will give the fish to a train staff and somebody will take the stuff to the desired station.

I think seal a bottle with compressed air is better and your stuff is not quite suitable.

Yes, provided that the bottle is big enough and the internal pressure isn't to great. Remember, it is not absolute pressure that destroys a vessel but relative pressure i.e. the pressure differential between vessel internal pressure and ambient pressure (atmospheric pressure) so make sure that you do only pressurize the bottle below its design limits.

Sealing the bottle is easy. You can drip wax onto the seal or use silicone cement.

Finally, don't use air to pressurize the bottle, use pure oxygen.

I drove 1000 miles with my 4 fish in a 5 gallon plastic water bottle. Used a cheap inverter and my aquarium air pump and air stone. Vented the bottle with a length of vertical air line such that it wouldn't spill water but air could escape.

Question1:

Yes bottles can hold a mix of water and compressed air. Pet bottles (like the coca cola 2 liter) can hold close to 10 bar. This is a scary situation for a fish, unless if it is one that is used to live in deep waters.

Can you put a fish in there? Yes when it fits through the opening. If that is a problem, don't worry you can also buy jar types bottles like used in laboratories. I have some here with a cover of 6 inches. These bottles are pressure tight.

If the fish is flat on arrival and the eyes are sticking out like with....... you overpressured it.

Question2:

You buy a cylinder of CO2 gas like you use to pressurize draft beer installations. If pure enough, you can also use the CO2 they use to (deep) weld steel. You need a connector nut, a pressure regulator, and a shut-off valve on the low pressure side.

1.Stick a plastic tube in the bottle in the water and release your load. The colder your water is, the better it works - screw the cap on tight quick.

2.You can also drop some liquid CO2 in the water, but that is more specialized and needs extra equipment.

3. You can do it also with frozen CO2 pellets. That is solid CO2. The so called "carbon glace"- excuse my French.

Good luck

Save on the co2 cost. just put the fish in the plastic bottle and "CAP" it tightly. They will die during transport and will be " Fresh! dead on arrival".

How about nonpressurized fish containers fed by a compressed air or oxygen cylinder with flow regulators and bubblers to each container?

Regardless of what scheme, you must calculate the amount of air or oxygen needed for the trip, with a suitable reserve in case of delays.

If you are so adamant to use pressurized bottles, buy a used bottling plant, place the fish in the bottle and pressurize and seal them.

BUT be aware that almost surely all your fish will arrive dead, since pressurization will affect them even if it is with oxygen.

I agree with the other people that you should stick with plastic bags inside of carboard boxes.

If you want to see professionals do it, look at the series TANKED on TV on sundays.