Decomposition of high protein aquaculture feed under variable oxic conditions

The microbial decomposition of nitrogen-rich organic matter in aquaculture ponds is affected by the oxic-anoxic conditions gradient at the soil–water interface as well as by resuspension practices. To investigate these interactions, the decomposition of a 49% protein fish feed was analyzed in 10 marine lab-scale systems with different exposures to aerobic and anaerobic conditions. The degree of coupling between oxic and anoxic conditions in the system had a strong effect on product accumulation and loss from the culture system. Pure oxic or anoxic conditions proved to be less favorable than mixed aerobic–anaerobic systems with respect to the metabolites accumulated in the system. Short 15-min resuspension events and a continuous alternation of oxic and anoxic conditions at 12-h time intervals proved to be the best options to minimize the accumulation of organic matter in the systems. The correct coupling of aerobic–anaerobic conditions in space and time is a key to maintain a good water quality condition for the cultured animals and also to improve the decomposition and recycling of organic matter, reducing the environmental impact from the effluents.