Preliminary Studies On Intermediate Culture Of Silverlip Pearl Oyster Pinctada Maxima And Effect Of Salinity On Oxygen Consumption And Ammonia- N Excretion Rates Of Pteria Penguin

Silvertip pearl oyster, Pinctada maxima, is a commercially important large-type species cultured for large-type pearls production attributed to its intrinsic excellent biological traits. Yet it cannot be cultured in large scale due to high mortality since 1985. Winged pearl oyster, Pteria penguin, is another large-type pearl oyster belonging to genus Pteria cultured for marbe pearl production, and has great potential to produce large-type round pearls. However, it is vulnerable to freshwater and thus can be easily attacked by heavy rains during typhoon season. To resolve these problems, the intermediate culture of silvertip pearl oyster juveniles and effect of salinity on winged pearl oysters were investigated to promote industrialization. The main results are as follows:1.Production of P. maxima larvae. Through promotion of mature, promotion of eggs and sperm release, fertilization and larval rearing, three batches of larvae were successfully produced, numbering 570000, 120000 and 1070000 larvae, respectively.2. Screening of optimal combination of algae for P. maxima juveniles. Algae Chlorella sp., Platmonas sp., Isochrysis zhanjiangensis, Spirulina sp. powder and some combinations were fed to silverlip pearl oyster P. maxima juveniles (the average shell length of 3.48mm, the average weight of 13.0mg). The results showed the highest growth rate of the shell length and body weight was the group of (Chlorella sp.+Platmonas sp.+Isochrysis zhanjiangensis+Spirulina sp. powder) after 40 days cultivation, with the shell length of 17.14mm (growth rate of 0.36mm/d) and body weight of 270.0mg (growth rate of 11.12mg/d), respectively, while the lowest growth rate of the shell length and body weight was the group of Chlorella sp., with the shell length of 12.42mm (growth rate of 0.22mm/d) and body weight of 120.0mg (growth of 4.24mg/d), respectively. The order of the growth rate of shell length and body weight was Chlorella sp. (group A) < Platmonas sp. (group B) < (Platmonas sp. +Isochrysis zhanjiangensis) (group C) < (Chlorella sp. +Platmonas sp. +Isochrysis zhanjiangensis) (group D) < (Chlorella sp. +Platmonas sp. +Isochrysis zhanjiangensis+Spirulina sp. powder) (group E). The difference of shell growth rates among groups were significant (P <0.05) except groups A and B and groups D and E. Meanwhile the differences among groups were also significant. On the other hand, the highest survival rate (85.8%) was observed in the group D and the lowest (48.1%) in group E and differed significantly (P < 0.05). The order of the survival rate was group E < group A < group B < group C < group D.3.Intermediate culture of pearl oyster P. maxima juveniles in deep waters. The juveniles (mean shell length: 4.11mm,mean shell height: 3.89mm,mean body weight: 0.0143g) were cultured in 3 m, 5 m, 7 m and bottom (~12 m) water depths with larvae density of 2000 ind./cage, and in densities of 500 ind./cage,1000 ind./cage,1500 ind./cage,2000 ind./cage and 2500 ind./cage under depth of 5m in Meishan sea area, Sanya Bay, Hainan Island. The results showed the highest growth rates of the shell length and body weight were occurred under the depth of 7 m after two months cultivation, with the shell length of 30.80mm (growth rate of 0.41mm/d) and body weight of 3.34g (growth rate of 36.69mg/d), and under the density of 500 ind./cage , with the shell length of 30.15mm (growth rate of 0.42mm/d) and body weight of 3.18g (growth rate of 31.90mg/d). In addition, the highest survival rates were observed in the bottom group (12 m) (17.7%) and at the density of 1500 ind./cage (15.3%), while the lowest in group 3 m (6.9%) and in group 2500 ind./cage (7.4%).4. Effect of salinity on oxygen consumption and ammonia- N excretion rates of Pteria penguin. The oxygen consumption and ammonia-N excretion rates of Pteria penguin were studied in order to provide information for management of culture practice. Mean body weights of the oysters tested were 7.46g (group A), 17.61g (group B) and 28.57g (group C). The results showed that the oxygen consumption and ammonia-N excretion rates in P. penguin were negatively correlated with its body weight under salinity ranging from 22 to 38, and their relationships could be expressed by a power function as: Y=aWb. The coefficient"a1"ranged from 3.795 to 9.275 for oxygen consumption rate, and"a2"from 7.949 to 9.775 for ammonia–N excretion rate. The coefficient"b1"ranged from -0.222 to -0.094 and"b2"from -0.452 to -0.208. When salinity is lower than 18, the oysters began to die. With the increase of salinity, the oxygen consumption rate also increased gradually. When the salinity was 34, the oxygen consumption rates reached the highest, being 6.03 mg / (g.h), 5.11 mg / (g.h) and 4.52 mg / (g.h), respectively. When salinity was over 34, the oxygen rate went down. With the increase of salinity, ammonia excretion rates went up. When salinity was 38, the ammonia excretion rates reached the highest, being 5.13 mg /(g.h), 4.64 mg /(g.h) and 3.82 mg /(g.h), respectively. When the salinity ranged from 22 to 34, the O: N increased with the increase of salinity. When salinity was 34, the O: N reached the highest, then went down when salinity over 34. These observations suggested that winged pearl oyster is vulnerable to low salinity, and its adaptable salinity range is from 26 to 34.