The marked difference in peroxide formation between hoki light and dark muscle is likely due to the considerably higher lipid contents in the dark muscle (recall from above 7.6 ± 2.3% vs. 0.6 ± 0.1% in the light muscle). This may also be why the saithe appears to be more durable over frozen storage when compared to the hoki; its total lipids for light and dark muscle were 0.6 ± 0.1% and 1.1 ± 0.1, respectively. The presence of active prooxidants such as hemoglobin (Richards & Hultin, 2002) could also explain the high peroxide value in the dark muscle of hoki, since bleeding on-board is not common practice for this fish species. The amount of haem iron content of the initial material was evaluated in the framework of a parallel study and was six-fold higher in the hoki dark muscle compared to the light muscle. Haem iron content in the saithe light and dark muscle was similar to the levels contained in the hoki light muscle (data not shown).