Four species of fish from Atlantic waters, Meronia americanus (perch), Cynoscion regalis (seatrout), Micropogon undulatis (croaker) and Pomatomus saltatrix (bluefish), were processed (gutted or filleted), packaged under carbon dioxide and refrigerated. Stability of the fish under the modified atmosphere preservation (MAP) system was compared to that of fish stored conventionally. Use of the MAP system resulted in a 45 to 55% increase in stability, primarily due to an extension in the lag phase of psychrotrophic organisms and to their reduced growth rate in the logarithmic phase. By the 10th day of storage, the conventionally packed fish always exhibited a 100-fold higher psychrotroph count than the CO2-packed fish. Levels of Vibrio parahaemolyticus were negligible in this MAP system and no Salmonella spp. or Staphylococcus aureus was detected, even at an abuse temperature (10°C) of storage. Positive evidence for preformed Clostridium botulinum toxin was lacking.

The relationship of low temperature survival of Vibrio paruhaemolyticus to the NaCl concentration and temperature of growth and suspending media was investigated. Morphological changes under these growth conditions were noted and the response of the organism in oysters stored at 4°C was also studied. The survival of V. parahaemolyticus was complete in solutions of l.OM and 0.5M NaCl, independent of exposure temperature, and few survivors were detected following exposure to 0.01M NaCl, regardless of exposure temperature or growth conditions. A loss of viability was observed in solutions less than or equal to O.OlM NaCl at 20°C and a further decrease in viability occurred upon exposure to these solutions at 4°C. No benefit was derived from prior growth in a medium containing a higher than optimal concentration of NaCl. However, a growth temperature of 20°C was more favorable to Vibrio survival than either 37°C or 10°C. The cold sensitivity of V. parahaemolyticus can, therefore, be offset if low temperature exposure occurs in a salt solution in excess of 0.5M NaCl and will also be diminished if growth takes place at 2O"C, a temperature close to that of its natural environment in summer.