Abstract:
This research involved the design and application of indoor recirculating aquaculture system (RAS) for Thai fish farmers. The study was divided into two parts which were larviculture system and fish culture system. With the first part, the proposed closed recirculating larviculture system consisted of 0.32 m3 fish cage and 30 m of BioCordTM biofilter media. Both components were placed in 2 m3 tank and the larviculture period was 24 days without water exchange. It was found that the system in this first trial could not maintain good water quality since accumulation of ammonia, nitrite and suspended solid was found. Thereafter, the system was improved for the second trial by separating nitrification tank from the larviculture tank and adding fine nylon net for sediment filtration. The results showed that the improved recirculating larviculture system had good performance in water quality control throughout 24 days experimental period even fish was reared at high density of 12 fish/L. Tilapia survival rate was 85% and fish growth rate was similar to that found in the production farm. The second part of this study was an evaluation of closed RAS for tilapia culture. The system consisted of culture tank with nitrification biofilter and tubular denitrification reactor. The proposed RAS was operated with initial fish density of 5 kg/m3 and culture period was 81 days without water exchange. The result indicated that recirculating system with nitrificationdenitrification treatments could maintain ammonia, nitrite and nitrate concentrations lower than 0.7, 0.76 and 16.94 mgN/L respectively. Hence, water exchange was not necessary. On the other hand, ammonia, nitrite and nitrate in control tank without water treatment system was as high as 18.2, 51.68 and 62.76 mgN/L, respectively. With this study, the final fish density was 12.8 kg/m3 and survival rate was similar at 92% in both control and RAS tanks. However, average fish weight in the recirculating system at the end of culture period was 1.03 g/day which was significantly higher than 0.8 g/day in control tank.