EFFECTS OF AERATION AND MIXING ON NITROGEN AND ORGANIC-MATTER TRANSFORMATIONS IN SIMULATED FISH PONDS

Both aeration and mixing are important design parameters in intensive aquaculture systems. The present study deals with the examination of the effect of each of these variables and their combined effect on the microbial transformations of organic carbon and of nitrogen. The most efficient organic carbon metabolism was found when both aeration and mixing were provided. Intensive organic matter degradation occurred also under strict anaerobic conditions, but not in systems with limited aeration. Aeration was essential for the existence of the nitrification process, however, the process was more efficient and started earlier when mixing was provided. Moreover, a denitrification process followed in aerated, non-mixed tanks, where an anaerobic bottom layer provided the conditions required for this process. Mixing of the water in fish ponds minimises the existence of non-desirable anaerobic zones in the pond and minimises ammonium accumulation in the water.