Herring is one of the most important fish species in the North Atlantic and Baltic Sea, with an annual catch exceeding 2 million tonnes. Although a large part of these fish is used for human consumption, as much as 85% of the herring is used for industrial production of fish meal and fish oil. There is a general wish to increase the utilisation of herring for human consumption. Thus, it was important to study the various parameters which influence the quality of herring, and in particular how these paramenters are controlled by biological factors. A major reason behind quality problems arising during post harvest handling of herring is its high content of compounds that efficiently catalyzes the development of rancidity, pigmentation, texture changes and loss of nutritional value.