Terry,
Ferdinand Cruz is presently doing experiments with various chemicals added to plastic bags. Since, it is necessary to seal the bags, aeriation is not an option. Even with aeriation in open systems, McFarland and Norris (1958) found that there was a drop in pH and an accumulation of total ammonia. Aeriation in an open system will reduce carbon dioxide to some extent but can not eliminate the accumulation of total ammonia.
McFarland and Norris (1958) found that the pH in sealed plastic bags containing the killifish in seawater declined rather quickly (over the first 8 hours) to a pH of about 6.1-6.2. The accumulation of dissolved carbon dioxide at low pH, and the low pH were believed to contribute to the 50% mortality noted at pH 6.1. They also reported that even though the bags contained adequate dissolved oxygen (from the oxygen gas added to the bags 3/4 oxygen by volume, 1/4 water) the fish could not utilize the oxygen at high carbon dioxide levels. It is believed that the accumulation of carbon dioxide from the fish acidifies the water by forming carbonic acid. Hence, this explains the drop in pH.
At low water pHs (near 6) the blood of the fish becomes more acidic and drops from about 7.8 to 7.0). This affects the ability of the fish haemoglobin to transport oxygen (Bohr and Root effects). Hence, the fish die from a lack of oxygen (asphyxiation).
Phone calls to importers in the Tampa area indicate that most exporters do not add anything to the water to control the pH (like buffers) or to control the accumulation of ammonia (ammonia detoxifying agent). Hence, I believe the fish are stressed by the drop in pH when fish are held in sealed plastic bags for 40 or more hours. There is scientific evidence that the drop in pH can induce the accumulation of stress hormones in the blood (e.g. ephinephrine, cortisol, glucocorticoids). The marked drop in pH and other changes mentioned occur while fish are transported to the villages on collection trips (some trips are for 7-10 days), while fish are held on shore in bags at the village level (often for 5 days or more), and when they are exported by air to destinations with longer transit times (eg, 35-50 hours).
Next, I will discuss efforts to use buffers (e.g. Tris Buffer) and sedatives (e.g. quinaldine, 2-phenoxyethanol) to stabilize the WQ in the bags associated with research to reduce mortality rates of fish in sealed plastic bags.
Peter