Utility of shell-closing strength as the indicator of good health in breeding and culture management of Japanese pearl oyster Pinctada fucata

Abstract

The aim of this study was to evaluate the suitability of shell-closing strength (SCS), a newly developed trait, as a physiological indicator in the Japanese pearl oyster Pinctada fucata. SCS is the load value necessary to open the shell of a pearl oyster to 10 mm using a shell opener. We developed a new instrument for the measurement of SCS consisting of a force gauge and a shell opener, and examined the relationship between SCS and physiological and nutritive indexes in pearl oysters. The results of the experiments showed that (1) oysters exhibiting good physiological conditions can be selected by using SCS as the indicator; oysters with higher SCS showed lower mortality, higher condition factor, and glycogen content in the adductor muscles than those with lower SCS; (2) SCS varies remarkably among genetic oyster lineages through the culturing period, indicative of the involvement of genetic factors in the determination of SCS; (3) the SCS of pearl oyster tended to increase with the body and the adductor muscle weights, although the protein and glycogen contents of the soft tissue exhibited typical changes during the period in which the water temperature is high (spring to summer). These results suggested that SCS is an efficient indicator of health of pearl oysters, and is useful for breeding and culture management of this species.