Great topic Dick, and certainly one that any serious hobbyist must have a firm grasp of knowledge on in order to maximize water environment and fish growth. Here is what I know so far, and please correct me if you guys find anything wrong.
As MCA mentioned, atmospheric air consists of 21% oxygen, 78% nitrogen, and 1% of trace gases. When we use atmospheric air to oxygenate our ponds, we can get about 20% dissolved oxygen (DO) saturation. This percent DO saturation is dependent on temperature, with oxygen being more easily dissolved in colder waters. It is also dependent on oxygen consumers in the body of water: biomass, biofilter, organic matter, and algae. I also agree with MCA that DO should not dip below 8% for this would result in growth retardation.
A decrease in DO may be due to several factors. The first factor is insufficient oxygenation. Another factor is algae releases O2 in presence of sunlight and consumes O2 in the absence of sunlight. Because of this DO varies throughout the day in ponds heavily populated with algae, with DO being the lowest in the morning and highest in the evening. Another factor is fish load. As we all know, the greater the fish load, the more oxygen is consumed.
Water saturation of DO is dependent on maximizing water surface area to air. This is achieved with the use of air pumps. Another way is via water agitation, be it via a waterfall or water propeller. Finally, there is the use of Bakki showers or trickle towers. In addition to oxygenating water, these showers and towers are great at removing nitrogen to the atmosphere as well.
Now, to get to Dick's question, here's what I have gathered. The use of pure oxygen to oxygenate water has been used by fish aquaculture for years. The goal is to have 100% DO, something that is not possible with atmospheric air, which contains only 21% O2, without exceeding gas pressure over 100%. As far as how much liters of O2 per ton/gallon of water, this is dependent on the fish load and, at least in fish culture, how much food is fed. According to Huisman et al (1974), for common carp, a warmwater species, 230 grams of O2 is consumed per kg of food fed.
Can we go overboard with oxygenation? The answer is yes. When total dissolved gas pressure (TGP) exceeds barometric pressure, a phenomenon called gas bubble trauma can occur. This is when water is so supersaturated that air bubbles occur in the blood and tissue of koi. This most commonly occurs in cold superaturated water.
Given the benefits of using pure oxygen in fish culture, it is not surprising that the use of pure oxygen in koi farms in Japan is gaining popularity. There are questions that remain to be answered:
1. How much does oxygen affect koi growth? We know that koi growth is minimal in waters that are <8% saturated. But do koi really need >20% DO saturation?
2. Is it cost-effective to use pure oxygens to oxygenate our koi ponds?
3. How safe is it to use oxygen cylinders in a common ponder's backyard.
I know that I am just scratching the surface when it comes to knowledge in this subject matter, but I hope that this will get us started and spark interest in those that are well versed in this area so that they can give their input. I have attached a few links of the use of pure oxygen in fish culture that I found on the web. I will also talk to a couple of fellows (one is a trout farmer and another is a zebra fish breeder for scientific research) that I know who I hope with give us more insights in this subject matter.
The Application of Pure Oxygen in Recirculating Systems http://www.pointfour.com/PDFs/Articl...ementation.pdf http://www.atlantech.ca/public/artic...20Quality3.PDF
05-24-2008
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