If you're serious about traporting some fish safely get youself a regulator that fits on an oxygen tank you can rent cheaply from a welding supply store. I get mine from a plumbing supply that supplies welders. Then purchase yourself a fine point diffuer (4 point is a good brand)available from any aquaculture supply catalog (see link below). Also order yourself a medical grade flow regulator between the regulator on the tank and your diffuser. A large cooler would work fine. Your oxygen line and connecters than can be purchased at a hardware store if not from the catalog. You can even attach two lines and use two coolers or more. Aquatic ecosystems has a tech line to walk you through it. Be sure to ask what to set the regulator at and ajust the flow meter at. Usually if you set the flow meter at a level just putting out some bubbles you're fine. As far as the regulator you don't want to exceed the recommended level for the flow meter. I believe it's 50 psi but I can't remember at this point. I have some reference on paper I dig out everytime I haul.

http://www.aquaticeco.com/

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.