Q. In response to a question about moving goldfish, you told the guy to put some water in a plastic bag, “blow into the bag” for air and then tie it up for transport. You were kidding when writing this stuff right? Remember back in physical science class: breathe in oxygen and exhale…carbon dioxide! I am sure that this guy’s fish died about 20 minutes after following your advice. I think you owe him a new fish for this false information.
I am writing this in detail so you can follow up. When you bag a fish you can catch atmospheric air (which contains 20-percent oxygen) in the bag. Or better yet, shoot oxygen from an oxygen cylinder, pump air from an air pump, or use a commercial oxygen supplement.
A. It is true that exhaled air contains a smaller percentage of oxygen and a higher percentage of carbon dioxide (CO2) compared with atmospheric air. The difference, however, is negligible (unimportant) when you blow up a bag of fish for short hauls.
Really, think about it. The rapid breathing that takes place when you blow up a balloon (or give CPR) does not allow for much gas exchange in the lungs. If it was true that exhaled air had dangerous concentrations of CO2, what do you think would happen when you gave CPR to someone? How many people have died from CO2 asphyxiation after receiving CPR?
Yes, an air pump would be a good alternative, but not if you did not have an air pump. Yes, an oxygen cylinder would be a good alternative, but not if you did not have one — or were afraid of a fire hazard. I agree that an oxygen-rich air mixture would be a superior choice for long hauls. But, frankly, opening the bag and breathing fresh air into it a few times would do just as well.
Fortunately, you can tell when bagged fish need “fresh air” because the bag deflates as CO2 replaces oxygen. It loses its tautness.
Fish are most likely to suffocate when the bag contains too much water. The volume ratio of air to water is more important under most conditions. Roughly, the bag should contain no more than 25 percent water. In fact, the great risk of transporting fish is not asphyxiation but 1) ammonia poisoning, 2) overheating or freezing, 3) leaks, 4) physical injury and 5) systemic stress from handling during the move.
plastic bags allow gas exchange through their semi-permeable surface anyhow ; both oxygen and carbon dioxide freely move between the bags layers