Growth performance and physiological parameters of the second generation selected and control groups of Pinctada martensii

In May of 2007, the second generation selected (SS) and control (SC) groups of pearl oyster Pinc- tada martensii were established by selecting 10% breeders with the largest and mean shell length, respectively, from the first generation selected group. Growth performance of the SS and SC groups were compared on the basis of measurement data at Days 8, 18, 60, 95, 195 and 365. On Day 365, 100 individuals (60.0-75.0 mm at shell length) were sampled from each group and then subjected to the experiment where physiological parameters such as filtrate rate, oxygen consumption and ammonia excretion were measured at 15, 20, 25 and 30 °C. The results show that the SS group had significantly larger mean shell length and shell height than the SC group at Days 8, 18, 60, 95, 195 and 365 (P <0.05). The genetic gains at different ages varied from 6.0% to 17.0% for shell length and 5.7% to 14.6% for shell height, respectively. At 15, 20, 25 and 30 °C, the SS groups had significantly larger filtrate rate than the SC group (P <0.05). At 15 and 25 °C, the differences in oxygen consumption rate between the SS and SC groups were not significant (P >0.05). At 20 and 30 °C, however, the oxygen consumption rate of the SS group was significantly larger than the SC group (P <0.05). At 15, 20, 25 and 30 °C, there were no significant differences in am- monia excretion rate between the SS and SC groups (P >0.05). The present results indicate that there existed considerable genetic variability in the base population and a further selection could be likely fruitful. Mass selection for faster growth might produce animals that had higher intake of metabolizable energy by virtue of faster filtrating behavior.