| Effects of temperature,salinity, combination of algae,substrate and exposure to air on early growth and development of panopea japonica were studied from April 2015 to October 2015. The study had the following main results.1.Observation of growth and development of Panopea japonicaPanopea japonica fertilized egg size was around 75~85μm. At the temperature of 19 ℃, salinity of 32, Panopea japonica fertilized egg via 18~20 h developed to trophore-larvae, 36 h developed to D-stage larvae, 9 D developed to umbo-larvae.Panopea japonica larval shell height/shell length increased from 0.75 to 0.88 with larvae developed from D-stage larvae to umbo-larvae,and then the rate decreased to 0.71,became closer and closer to adult.2. Effects of temperature on early growth and development of panopea japonicaThe optimum incubation temperature of Panopea japonica fertilized egg was around 16~22℃. 16~22 ℃ was the optimum temperature range for Panopea japonica planktonic larvae.When the water temperature was higher than 22 ℃,the larvae of Panopea japonica couldn’t survive for long time.And when the water temperature was lower than 16 ℃,the larvae grew slowly and had a low metamosphsis rate. 16~22 ℃ was the optimum temperature range for Panopea japonica metamorphosis stage larvae.The larvae could also metamorphose when the temperature was 13 ℃,but the metamorphosis rate was lower than it when temperature was at the range of 16~22 ℃. When the water temperature was 25 ℃,both the metamophosis rate and survival rate were low.3. Effects of salinity on early growth and development of panopea japonicaThe optimum incubation salinity of Panopea japonica fertilized egg was 32. 30 was optimum salinity for the planktonic larvae and when the salinity was lower than 25,the larvae couldn’t survive for long time. 30 was optimum salinity for the metamorphosis stage larvae. Gradually-changed salinity could improve the tolerance of Panopea japonica juvenile at low salinity.By gradually-changed salinity acclimatization,a part of Panopea japonica juvenile at the salinity of 20 could survival for long time.The growth and survival rate of the juvenile at the salinity of 25 were little lower than them at the salinity of 30.4. Effects of density on early growth and development of panopea japonicaThe optimum incubation density of Panopea japonica fertilized egg was 3 /mL. The appropriate breeding density for the planktonic larvae was 3~6 /mL.5. Effects of substrate on early growth and development of panopea japonicaPure sand substrate had significantly higher growth rate,survival rate and metamorphosis rate for the larvae than substrate contained mud. Under different substrate to breeding Panopea japonica juvenile,sand with mud at the rate of 1:1 obtained the best survival rate,and pure sand obtained the best growth.Suitable substrate for the juvenile should be sand with mud which sediment was more than 50 %.6. Effects of other factors on early growth and development of panopea japonicaFor planktonic larvae,Isochrysis galbana with Nitzschia closterium at the rate of 2:1 obtained the best feeding result.For metamorphosis stage larvae,Isochrysis galbana with Nitzschia closterium at the rate of 1:1 obtained the best feeding result.The planktonic larvae of Panopea japonica had the best growth and survival rate by the concentration of garlic extracts of 4 mg/L.The survival rate of the juvenile exposure the air at 10 ℃ was higher than it at 0 ℃ and 20 ℃.And the larger juvenile had more tolerance for exposure than the smaller juvenile.After exposured to the air,brought the smaller juvenile back to original environment for breeding, indicating that there was compensatory growth. |
