Better aeration for aquaculture
Low oxygen levels affect fish farms especially in the summer and early autumn when stocking densities are high. Farmers may be compelled to stop feeding their stock to avoid fatalities, leading to reduced growth rate. Alternatively, they may employ paddle wheels or even inject pure oxygen directly into the water to increase dissolved oxygen levels. However, the use of pure oxygen incurs high production costs. The aim of the AIRX (Oxygenation by efficient air diffusion system for aquaculture farms (cages and earthen ponds)) project was to develop a system to control dissolved oxygen levels. This will be used in large aquacultural facilities such as sea cages, earth ponds, large tanks and raceways. Current aeration devices used in ponds have low efficiency, and there are no realistic options available for sea cages. AIRX developed a hose grid system capable of dispersing air bubbles horizontally across a large area as well as vertically in the water column. Oxygen can be directed to areas where additional oxygen is needed, ensuring that all fish have equal access. The homogenous distribution of small bubbles ensures the most efficient transfer of oxygen into the water. In addition, the lack of upwelling currents will increase contact time and therefore transfer efficiency. The use of the AIRX system will reduce oxygenation costs by 75 % and give a higher growth rate of stock, an improved feed conversion rate, higher production capacity and reduced mortality, especially during periods of high temperature/low oxygen concentration. It will also reduce stress and generally improve fish welfare, as well as increasing carrying capacity in terms of organic load that can be decomposed in the case of fish ponds, and reduced settling of waste beneath cages. The target market for the oxygen diffusion system is cage and earthen pond farmers in the Mediterranean who rear sea bass and sea bream. The diffusion system will help them to avoid the problems associated with low oxygen content and resulting loss of income. The response of potential end-users has been positive. They include cage farmers from Malta and Sardinia, as well as Germany, Iceland, Finland and the US. Furthermore, a demonstration project was set up in Vietnam for the pond culture of shrimp and fish. Another demonstration project used the system for lake restoration applications in Norway.
