1Fisheries Research Center, Ehime Research Institute of Agriculture, Forestry and Fisheries, Uwajima, Ehime 798-0104, 2Tamaki Station, National Research Institute of Aquaculture, Fisheries Research Agency, Tamaki, Mie 519-0423, Japan
In order to improve the pearl quality produced by autumn nucleus insertion in hybrid pearl oysters, we investigated the physiological condition of hybrid pearl oysters during the preconditioning period. Two-year-old hybrid pearl oysters were treated at the preconditioning stage and normal stage (control) and sampled at 0, 5, 9, 15, 19, 26, 30, 40 and 50 days after being treated. The sampled pearl oysters, in which a mantle graft and nucleus had been implanted, were measured for proximate composition and carbohydrate-metabolizing enzyme activity in the adductor muscle, and the produced pearls were evaluated. The glycogen content of the treated pearl oysters decreased from day 19 to the end of the experimental period. The enzyme activities of GPase, PFK and PK of the treated pearl oysters increased, whereas the MDH activity decreased from day 40 to day 50. The commercial pearl production rates (%) at day 5, 9, 15 and 19 were higher than at other days and the glycogen content was around 2%. These results suggest that the glycogen content of the adductor muscle is a useful index of the preconditioning condition in hybrid pearl oysters at autumn nucleus insertion.