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Why aeration is a very important management tool for aqua farm.
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Author : ECOWATER AQUA
Update time : 2022-10-24 11:18:19
Why aeration is a very important management tool for aqua farm from ECOWATER AQUA
Mechanical aeration can be used to prevent low concentrations of dissolved oxygen. However, overabundant phytoplankton in aerated ponds can cause unacceptably large increases in pH and associated increases in NH3 concentration. Elevated pH in ponds also favors the growth of blue-green algae (called cyanobacteria by many biologists), because these organisms tend to grow better than other kinds of algae at a high pH. Aquaculture ponds often have phytoplankton communities in which one or a few species of blue-green algae make up 90 percent or more of the algal community.
Some species of blue-green algae – especially species of Anabaena and Oscillatoria – can excrete odorous compounds into the water that may be adsorbed by shrimp and fish to impart a bad taste (off-flavor) to their flesh. Some blue-green algae – especially Oscillatoria, Microcystis, and Aphanizomenon – can produce algal toxins that can stress or kill the culture species.
Blue-green algae also may rise to the surface by virtue of vacuoles in their cells that can fill with gas when high algal abundance limits light penetration into the water. Near the surface, high rates of photosynthesis may cause the pH to increase enough to cause mortality to the algae. This phenomenon often is called a phytoplankton die-off. Such events may cause dissolved oxygen concentration to fall to unacceptable levels in ponds without mechanical aeration. The likelihood of phytoplankton die-off is minimized in aerated ponds because water circulation tends to minimize the occurrence of surface algal scums, and oxygenation by aerators prevent low dissolved oxygen concentration following die-offs.
There is no effective means of preventing a high abundance of phytoplankton in ponds that receive large inputs of nutrients. At feeding rates above about 30 kg/ha/day, nighttime dissolved oxygen depletion often will become a limiting factor – higher daily feeding rates are possible in un-aerated ponds for tilapia and a few other species. With mechanical aeration, much higher feeding rates may be used, but it is critical to match aeration rate with feeding rate for most warmwater species to avoid dissolved oxygen below 3 or 4 mg/L. Unless this is done, the producer has more fish in the pond, but water quality will be suboptimal and stress the animals.
Mechanical aeration will not avoid high pH, elevated carbon dioxide concentration in the morning, high NH3 concentration in the afternoon, or the occurrence of blue-green algae responsible for off-flavor and algal toxins. Ponds with low alkalinity can be limed to minimize daily swings in pH, but even so, the pH may reach undesirably high levels in the afternoon, if phytoplankton is abundant.
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