Nile tilapia (Oreochromis niloticus) farmed in recirculation aquaculture system (RAS) was filleted and packaged in 100% air and 50% CO2: 50% N2 modified atmosphere (MA) prior to storage at 1˚C and -1˚C for up to 27 days. Fillets were sampled regularly and analysed for headspace gas composition, sensory and microbial changes. Shelf life varied with apparent relation to storage temperature, package atmosphere and microflora. Pseudomonads were reported as the main spoilage organisms in tilapia fillets during chilled storage conditions. Sensory analysis of cooked samples as well as microbial growth indicated fillets packaged in 100% air had a shelf life of 13-15 days during storage at 1˚C and 20 days at -1˚C. At the end of shelf life in 100% air packaged groups, TVC and pseudomonads counts reached log 7 colony-forming units g-1 in flesh. Whereas in 50% CO2: 50% N2 packaged fillets, the lag phase and generation time of bacteria was extended and recorded counts of < log 4 colony-forming units g-1 up to 27 days of storage at both 1˚C and -1˚C. However, 50% CO2 : 50% N2 conditions restricted fillets shelf life to 23 days based on sensorial changes mainly fillets colour characteristics.