Other studies on the effects of flaxseeds on rancidity development in frozen whole mackerel (Stodolnik et al., 2005) and ascorbic acid in frozen herring (Hamre et al., 2003) and so also the effects of vitamins C, E and ascorbic acid in frozen horse mackerel (Sarkadei and Howell, 2008) reported significant increase of peroxide value in all samples during storage period. But increase of peroxide value in antioxidant treated samples was significantly lower than that reported for control samples. PV measurements are not reliable for assessing oxidation progress of highly unsaturated oils such as fish oils. This is probably because the peroxides that form initially are unstable and react quickly to form secondary oxidation products. For this reason, the PV should be used in conjunction with other methods (Sánchez-Alonso and Borderias, 2008). The thiobarbituric acid (TBA) test is widely used to quantify lipid oxidation products in fish meat. Secondary lipid oxidation products, as reported by the TBA-i, presented low values at the beginning of the study (Fig. 5) and gradually increased during frozen storage (as in the case of PV). A significant increase in TBA-i value was observed for control and CA-treated samples (p