Two strains of Shewanella spp. were isolated from cod fillets packed in modified atmosphere (60% CO2, 30% O2, 10% N2). One of the strains was identified asShewanella putrefaciens. The other strain could not be fully identified but was determined as a Shewanella spp. different from S. putrefaciens. The effect of modified atmosphere (CO2, O2) on the growth of the two strains and on the reduction of TMAO to TMA was studied using solid medium from fish extract packed under variable mixtures of CO2, O2 and N2. All the samples were incubated at 7°C for 7 days. The Shewanella-like strain was shown to be a stronger TMAO reducer and was more resistant to CO2 than S. putrefaciens per se. Modified atmosphere packaging of marine fish can inhibit the growth and TMAO-reducing activity of S. putrefaciens when 50% of CO2 together with 10% of O2 are introduced into the packaging atmosphere. The growth and TMAO-reducing activity of the Shewanella-like strain can be inhibited when higher proportions of CO2 together with as high as possible proportions of O2 are introduced into the packaging atmosphere. It is suggested that a combination of 60-70% CO2 and 30-40% O2 is introduced into the packaging atmosphere in order to prevent TMA production by Shewanella spp
