Oxygenation is better than aeration for long haul transport of fish.

Fish need oxygen dissolved in the water in order to breathe. This can be done by two methods. Aerate the tank by using an air pump to pump atmospheric air into the water; alternatively, this can be done by injecting oxygen into the water. During transport, fish are held at higher densities for economic reasons. Supplemental oxygen would therefore need to be provided. This paper provides good evidence that it is better to oxygenate tanks rather than aerate them.

I’ll explain why this is so. When transporting fish in water, they continually excrete ammonia. When this enters the water, it is found in two forms, ammonium and ammonia, depending on the water pH. Ammonia is toxic to fish when in high concentrations. There is a greater proportion of ammonia when the pH is high (under more alkaline conditions). What saves the fish from ammonia build up is that they also produce carbon dioxide. When carbon dioxide enters the water, it will lower the pH (make the water more acidic). This effect actually reduces the proportion of ammonia that is in the water. Heavy aeration can cause the carbon dioxide to escape, leading to elevation of pH and in turn, increase the proportion of toxic ammonia and fish losses can result. Thus, it is better to keep the carbon dioxide in the water to maintain the lower pH in order to have a greater proportion of the ammonia in the ammonium form. This means you need to provide oxygen to the water with less turbulence. This means injecting oxygen.

This same suite of chemical reactions also occur in bagged fish. Keeping the carbon dioxide in (and maintaining the low pH) is the reason for NOT opening the bag while you’re floating the bag for temperature equalisation.

Aquacultural Engineering
Volume 55, Number 3 (July 2013)
	Impact of aeration and alkalinity on the water quality and product quality of transported tilapia—A simulation study
	Authors:	John Colt, Eric Kroeger
	Author Affiliations:	no affiliations available
	Source:	Aquacultural Engineering, Volume 55, Number 3 (July 2013)
	Page Numbers:	46 – 58
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	•Air aeration resulted in lowest CO2, highest pH, and highest NH3concentrations.•At high alkalinities, the “Air” treatment was unable to maintain adequate DO levels.•Oxygen aeration resulted the highest DO, highest CO2, lowest pH, and lowest NH3.•NH3was higher in the “High Alkalinity” treatments because of higher pH.•Increased mortality was observed in the air aeration treatments.
	Citation:	John Colt, Eric Kroeger . Impact of aeration and alkalinity on the water quality and product quality of transported tilapia—A simulation study. Aquacultural Engineering, Volume 55, Number 3 (July 2013), pp. 46-58, <http://ejournals.ebsco.com/direct.asp?ArticleID=490884D54065027B9A66&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=490884D54065027B9A66