Histamine Production by Photobacterium spp. in Tuna and Mahi-mahi under Various Storage Temperatures

• Inoculated fish tissues had histamine levels ≥200 ppm within 3-9 days at 4°C. • Inoculated fish tissues had histamine levels ≥200 ppm within 1-10 days at 10°C. • Inoculated fish tissues had histamine levels ≥200 ppm within 12-38 hours at 20°C. Histamine-producing bacteria (HPB) generate histamine in decomposing scombrotoxin-forming fish tissue. Elevated histamine levels (≥200 ppm) can cause scombrotoxin fish poisoning in humans who consume decomposed fish and fishery products. In this study, four psychrotrophic Photobacterium species, P. kishitanii , P. angustum , P. aquimaris , and P. phosphoreum , were evaluated in pure culture for histamine production at 4, 10, and 20°C. P. kishitanii and P. angustum demonstrated the most prolific histamine production in vitro and were inoculated into tuna and mahi-mahi tissue to determine the time at which histamine exceeded FDA guidance levels at 4 and 10°C for P. kishitanii and 10 and 20°C for P. angustum . Current U.S. FDA guidance levels for histamine are ≥200 ppm for human health hazard and ≥35 ppm for evidence of decomposition. Samples were analyzed for histamine with a modified AOAC fluorometric method. Tuna inoculated at 10 2 , 10 4 , and 10 6 CFU/g P. kishitanii , accumulated histamine levels ≥200 ppm after 7, 5, and 3 days at 4°C and 2, 2, and 1 day(s) at 10°C, respectively. Tuna inoculated at 10 2 , 10 4 , and 10 6 CFU/g P. angustum , contained histamine levels ≥200 ppm after 6, 4, and 2 days at 10°C and 24, 20, and 12 h at 20°C, respectively. Mahi-mahi inoculated at 10 2 , 10 4 , and 10 6 CFU/g P. kishitanii , accumulated histamine levels ≥200 ppm after 9, 6, and 4 days at 4°C and 3, 3, and 2 days at 10°C, respectively. Mahi-mahi inoculated at 10 2 , 10 4 , and 10 6 CFU/g P. angustum , contained histamine levels ≥200 ppm after 10, 9, and 3 days at 10°C and 38, 16, and 12 h at 20°C, respectively. Tissues contained ≥200 ppm histamine after 3-9 days under storage temperature of 4°C but as early as 12 hours when held at elevated temperatures. Understanding how storage conditions affect HPB growth and histamine production in scombrotoxin-forming fish is important to inform guidance for recommended fish storage conditions and to mitigate risks.