Are morphometric indices accurate indicators of stored energy in herring Clupea harengus?

The accuracy of the morphometric indices Fulton's K, somatic K and relative condition factor, K-n, as measures of individual North Sea herring Clupea harengus muscle fat content was investigated using the Distell Fish Fat meter. The accuracy of fat-meter readings from an individual fish was validated by comparison with Soxhlet extraction analysis. The studies conducted demonstrated that Fulton's K is not consistently or strongly correlated with individual C. harengus muscle fat content, as defined by the fat-meter estimates. The study shows that somatic K and K-n may be better indices of individual North Sea C. harengus muscle fat content than Fulton's K. These morphometric indices, however, should only be used after prior validation against a more direct measure of fat content.