EFFECT OF SELECTION FOR SHELL COLORATION ON GROWTH-RATE AND MORTALITY IN THE JAPANESE PEARL OYSTER, PINCTADA-FUCATA-MARTENSII

Effects of inbreeding on the growth rate and mortality are suggested on the basis of results of comparative growth experiments for a line of the Japanese pearl oyster, Pinctada fucata martensii, selected for white shell color in the prismatic layer. Growth in shell height, whole weight and mortality were measured using one inbred white cross and two hybrid white/brown crosses held in pearl nets under different densities. Analyses were conducted at the juvenile (3-12 months of age) and adult (12-20 months of age) stages. The growth rate was estimated by the differences between measurements at the start and after 4, 5, 6, 8 and 12 months in the juvenile experiment, and after 17 and 20 months in the adult experiment. Growth in whole weight and survival were significantly inferior in the inbred white crosses than in two hybrid crosses. With the exception of one case, there was no observation in which the performance of an inbred cross was significantly superior to that of the two hybrid crosses. There were significant effects of density on growth rate in weight, shell height and mortality.