The Diurnal Trend of Water Quality in the Semi-Outdoor Recirculating Aquaculture System for the Red Tilapia (Oreochromis sp.) Production

      With the increasing global population, ensuring food security has become one of the major global challenges, particularly in relation to protein food sources. Aquaculture activities are generally considered a potential alternative for providing protein-rich food. However, conventional aquaculture production systems require substantial water usage, which is often scarce in certain areas. Recirculating aquaculture systems (RAS) have emerged as a water-efficient method of aquaculture production. However, literature on diurnal trends of water quality within RAS is still limited, making it challenging to establish standard operating procedures (SOPs) for water quality monitoring in RAS. This study aimed to examine the diurnal patterns of several water quality parameters in a semi-outdoor RAS used for the cultivation of the red tilapia (Oreochromis sp.). Water quality parameters were measured every three hours over a 24-hour period. The results showed distinct diurnal trends for each observed parameter, including total ammonia nitrogen (TAN), un-ionized ammonia (NH₃), dissolved oxygen, oxygen deficit, pH, and temperature. TAN, dissolved oxygen, and pH exhibited higher values in the morning (6:00–9:00). In contrast, temperature and oxygen deficit were generally higher in the evening (18.00–21.00). Based on these trends, the best times for water quality monitoring in semi-outdoor RAS are predicted to be at 09.00 and 18.00. Further research is needed, especially in locations with different climates and altitudes, to validate and expand these findings.