Light muscle, dark muscle, and skin from herring (Clupea harengus) were stored separately or as intact fillets at −18°C. After 0, 2, 8, 12, and 18 wk, all tissues were analyzed for conjugated dienes (A 234 ) and lipid hydroperoxides. In tissues stored separately, total absorbance at 268 nm (A 268 ) and lipid-soluble fluorescent oxidation products (FP) were also monitored. Further, prior to storage these tissues were subjected to measurement of total lipids, lipid classes, fatty acid pattern, α-tocopherol, iron, copper, selenium, and total aqueous pro-oxidative activity. When light muscle, dark muscle, and skin were stored as intact fillets, the following ranking order was seen for A 234 and levels of lipid hydroperoxides at the end of the storage period: skin > dark muscle > light muscle. The corresponding ranking order for tissues stored separately was: dark muscle > skin > light muscle, whereas for A 268 and FP the orders were: dark muscle > light muscle > skin and light muscle > dark muscle > skin, respectively. The compositional data obtained indicate the highest level of pro-oxidants in dark muscle and the highest level of polar lipids in light muscle. These observations reveal that pro-oxidants, to a greater extent than lipid composition, influence the increase in A 234 , hydroperoxides, and A 268 , whereas the reverse seems to be true for the increase in FP. The results also point to the strong influence from oxygen contact and tissue interactions on the progress of lipid oxidation in herring during storage. JAOCS 75, 581-590 (1998).A strong limiting factor in the processing and storage of herring (Clupea harengus) is the susceptibility of its lipids to oxidation. This susceptibility is caused by the powerful pro-oxidative systems present in fish and the highly unsaturated nature of the lipids (1). As a result, alterations in flavor, texture, nutritional value, and color may develop (2). Because both economic and nutritional factors call for an increase in the production of food from herring, there is a desire to understand, and thereby avoid, any changes in quality that result
