Proteolytic activities of ventral muscle and intestinal content of North Sea herring (Clupea harengus) with full and emptied stomachs

The aim of the work was to examine the effect of allowing herring (Clupea harengus) to empty the stomachs prior to being taken on board the fishing vessels, on the proteolytic activities in extracts of ventral muscle and of intestinal content. The proteolytic activities were examined by gelatin zymography and by incubating the extracts with isolated myosin heavy chain (MHC) protein. Extracts from herring with full stomachs showed strong gelatinolytic and MHC degrading activities particularly in extracts from intestinal contents. Extracts from fish that had been allowed to empty their digestive system for 19 h had reduced activities, which was most noticeable in the ventral muscle extracts. The activities from the ventral muscle did not originate endogenously post-mortem, as shown by the fact that ice storage for 24 h of isolated ventral muscle did not display the activities, while ventral muscle extract from ice-stored whole fish for 24 h did.