Seasonal variation in quality and chemical composition of the muscles of the spotted mackerel Scomber australasicus and Pacific mackerel S. japonicus

The quality of fish muscles is known to vary with the season. The characterisation of such seasonal variations is important for the development of fish products of high commercial value. In this study, seasonal variations and correlations between muscle toughness and chemical composition in the muscle of two fish species, the spotted mackerel Scomber australasicus and the Pacific mackerel S. japonicus, were examined. Muscle toughness and chemical composition differed between these two mackerel species. Muscle toughness, as determined by the breaking strength, was correlated with muscle pH in both the spotted mackerel and Pacific mackerel (r=0.34 and 0.57, respectively). In addition, muscle toughness was negatively and weakly correlated with cathepsin L activity in the Pacific mackerel (r=-0.23). Around the spawning period, muscle quality decreased in both species. These findings suggest that muscle toughness is influenced by an acidic pH in both the spotted mackerel and Pacific mackerel and additionally by cathepsin L activity in the Pacific mackerel around the spawning period.