ENVIRONMENTAL REQUIREMENTS FOR DIFFERENT PRODUCTION INTENSITIES OF NILE TILAPIA (Oreochromis niloticus) IN RECIRCULATING AQUACULTURE SYSTEMS (RAS) IN KENYA
Kenya has a high potential for aquaculture. Through Flow systems such as raceways and ponds are the main types of aquaculture majorly practiced in Kenya. Due to the ever dwindling land and water resources, flow through system are becoming unsustainable for aquaculture production. RAS offer a better option to increase aquaculture production with the limited land and water resources while minimizing water pollution. The biggest challenges in RAS is to maintain favorable water quality for the fish to thrive. The practice of RAS in the country is minimal with improper matching of RAS components and production densities leading to the system failure. This study aimed at evaluating environmental requirements for different production intensities of Nile tilapia in a RAS set in a greenhouse. In this experiment, both production intensities and water flow rates were varied and the water quality parameters (Dissolved Oxygen, ammonia, pH, EC and temperature) monitored. Tilapia stocking intensities were varied between 2kg/m3and 10kg/m3 while flow rate was varied from around 2.0l/min and increased at intervals of 1l/min or 1.5l/min to the maximum attainable flow rate. Crushed pumice rock packed in a 1000L tank was used as the biofilter. The study showed that, ammonia removal reduced with increasing flow rate with removal rates ranging from 75% at low flows to 2% at high flows. pH and electrical conductivity increased with increasing flow rate with R2 ranging from 0.4 to 0.9 for both. Dissolved oxygen seemed to increase with flow rate and ranged between 5.2±2.4mg/l. Fish appetite was highest between 25-30˚C. The optimal environmental requirements for Nile tilapia were found to be 3mg/l dissolved oxygen, 7.0 pH, and 27˚C of temperature and 0.03mg/l of ammonia at different flow rates for each stocking density. Similar studies to be carried out for other fish species such as African cat fish.