Anguillid eels generally exhibit catadromous migration between oceanic spawning grounds and freshwater growth habitats, but some individuals remain in coastal or estuarine saline waters for growth. This migratory plasticity had been considered to be a conditional strategy based on individual energetic status during the glass eel stage. Several studies have examined whether salinity-based habitat selection is linked to individual body conditions, but while frozen specimens of European eels showed this relationship, anesthetized samples of American eels did not. Here, we report that freezing preservation under different salinity levels influences body-condition evaluation in Japanese eels. Behavioral tests of Japanese eels did not reveal significant differences in anesthetized body conditions between those choosing saltwater and those choosing freshwater. In conclusion, the body conditions of glass-eel-stage Japanese eels are unlikely to be associated with their salinity-choice propensity.

The basic contractile unit of muscle, the sarcomere, will contract as the muscle goes into rigor post-mortem. Depending on the conditions, such as the rate of pH decline, the cooling rate and the mechanical restraints on the muscles, this longitudinal shortening will result in various post-mortem sarcomere lengths as well as lateral differences in the distances between the myosin and actin filaments. This shortening is underlying the phenomena described as rigor contraction, thaw rigor, cold shortening and heat shortening. The shortening in combination with the molecular architecture of the sarcomere as defined by the myosin filaments and their S-1 and S-2 units, the interaction with the actin filaments, and the boundaries formed by the Z-disks will subsequently influence basic meat quality traits including tenderness and water-holding capacity. Biochemical reactions from proteolysis and glycogen metabolism interrelate with the sarcomere length in a complex manner. The sarcomere length is also influencing the eating quality of cooked meat and the water-holding in meat products.