Acute and chronic effects of salinity on nitrification in a recirculating aquaculture system with açaí seeds (Euterpe oleracea) as biological media

Introduction The Blue Amazon represents an extensive coastal zone with high biodiversity and wide salinity variation, which poses challenges for marine fish farming, particularly regarding the efficiency of biofilters in recirculating aquaculture systems (RAS). In this context, açaí seeds ( Euterpe oleracea ), previously evaluated in freshwater, emerge as a promising alternative for use as filter media under different salinity conditions. The objective of this study was to evaluate the potential of açaí seeds as substrate in RAS biofilters, analyzing their acute and chronic impact on the physicochemical parameters of water and the removal of ammonia, nitrite and nitrate over 28 days. Methods The experiment was conducted in six independent systems (three aquaria each), subjected to salinities of 0, 7, 14, 21, 28 and 35‰. After Acute (0, 20, 40, 60,80,100 and 120 minutes) and chronic (2,3,4,14,21 and 28 days) salinity change, water samples were collected to measure physicochemical quality and to assess nitrification efficiency and nitrogen compound removal. Results Higher oxygen consumption and ammonia clearance were observed at 0, 7 and 14‰ after 120 minutes of salinity change, while nitrate accumulation was significantly higher in freshwater. In long term, after 28 days, ammonia clearance was significantly lower at 35‰, though nitrate accumulation was not affected by salinity. The highest ammonia removal rates were recorded in the 0‰ and 7‰ treatments. Discussion The results demonstrate that açaí seeds are capable of removing ammonia after a few minutes and can sustain the growth of nitrifying bacteria under different salinity levels, although more efficiently in low salinity waters (seven times).