Lipid oxidation of Nile tilapia muscle during iced storage was monitored by measuring PV and TBARS values (Fig. 2). Primary oxidation was monitored by the changes in PV as shown in Fig 2(A). PV of fresh sample was 1.67 mg hydroperoxide/kg, suggesting that lipid oxidation occurred during postmortem handling to some extent. Continuous increase in PV was observed throughout iced storage of 18 days (P < 0.05). Oxidation of unsaturated fatty acids takes place in the presence of pro-oxidants like heme proteins during storage. In fish, especially in lean fish, the phospholipid membrane is believed to be the key substrate for lipid oxidation due to its highly unsaturated fatty acid composition (Undeland, Stading, & Lingnert, 1998). Pacheco-Aguilar, Lugo-Sanchez, and Robles-Burgueno (2000) reported that peroxide formation of oily Monterey sardine increased up to 15 days of storage at 0 °C. Nevertheless, the slight decreases in PV were found in seabass and red tilapia at the end of iced storage (day 15), plausibly due to the decomposition of hydroperoxide to other compounds. The increase in PV correlated with the increased amount of non-heme iron (Fig. 1(B)), which more likely acted as a pro-oxidant in fish muscle. Heme dissociation, heme destruction and iron release play a role in the acceleration of lipid oxidation.