THE EFFECT OF HIGH HYDROSTATIC PRESSURE (HHP) TREATMENTS (450 AND 550 MPA FOR 3 AND 4 MIN AT 20 °C) ON THE MICROBIAL BEHAVIOUR AND SHELF-LIFE EXTENSION OF CHILEAN JACK MACKEREL (TRACHURUS MURPHYI) DURING CHILLED STORAGE AT 4 °C WAS STUDIED. AEROBIC MESOPHILIC AND PSYCHROPHILIC MICROORGANISMS, AS WELL AS HYDROGEN SULPHIDE-PRODUCING BACTERIA (MAINLY SHEWANELLA PUTREFACIENS) WERE ENUMERATED IMMEDIATELY AFTER TREATMENT AND DURING SUBSEQUENT STORAGE AT 4 °C. PHYSICOCHEMICAL PARAMETERS SUCH AS PH AND TMA-N WERE ALSO RECORDED. RESULTS SHOWED THAT HHP TREATMENTS WERE EFFECTIVE IN REDUCING INITIAL MICROBIAL COUNTS AND DELAYED MICROBIAL GROWTH DURING REFRIGERATED STORAGE. HHP TREATMENTS WERE ALSO EFFECTIVE IN DELAYING TMA-N PRODUCTION IN THE FISH DURING STORAGE. AS A RESULT, MICROBIOLOGICAL SHELF-LIFE WAS SIGNIFICANTLY (P < 0.05) EXTENDED FROM ~ 6 DAYS (CONTROL SAMPLES) TO ~ 29 AND ~ 40 DAYS IN PRESSURISED SAMPLES AT 450 MPA/3 MIN AND 550 MPA/4 MIN, RESPECTIVELY.