养殖密度对毛蚶幼虫生长及存活的影响

Effect of stocking density on growth and survival of bloody clam(Scapharca subcrenata)larvae

为探讨毛蚶（Scapharca subcrenata）幼虫养殖的最佳密度，本研究设定了5个不同的放养密度（2、5、8、14、20ind／mL）．养殖实验从D型幼虫阶段一直持续到幼虫完成附着变态。实验结果表明，随着放养密度的增加，水体氨氮浓度、亚硝酸盐浓度显著升高（P〈0．05）；幼虫密度为20ind／mL时，分别达到最大值0．089mg／L和0．008mg／L。溶解氧浓度则随幼虫密度的增大呈现下降的趋势，幼虫密度达到14、20ind／mL时，显著低于其他密度组（P〈O．05）。幼虫的生长速率随放养密度的增加显著下降，5-8ind／mL为幼虫最佳生长密度。幼虫的存活率也随着放养密度的增加显著下降（P〈0．05），当幼虫的放养密度为20ind／mL时，存活率仅为35％。放养密度为8ind／mL时，幼虫的附着密度最大，且在附着基下层的附着密度显著高于中层和上层（P〈0．05）。同时，随着放养密度的增加，幼虫附着变态的时间被延长，附着变态规格也显著减小p〈0．05）。因此，综合考虑各种要素，规模化苗种生产中幼虫的培育密度控制在5-8ind／mL较为适宜。

We performed experiments at stocking densities of 2, 5, 8, 14, and 20 larvae/mL to determine optimal larval density for hatchery culture of bloody clam, Scapharca subcrenata. Larval developmental stages from D-veliger to settlement and metamorphosis were included. The results indicated that total ammonia nitrogen （TAN） and nitrite increased significantly with increasing stocking density （P〈O.05）. TAN and nitrite levels in the 20 lar- vae/mL group reached maximum values of 0.089 mg/L and 0.008 rag/L, respectively. Dissolved oxygen （DO） concentrations decreased significantly with increasing stocking density （P〈0.05）, and DO concentrations in the 14- and 20-1arvae/mL groups were lower than those in the other treatments. Larval growth decreased significantly with increasing stocking density （P〈0.05）. A density of 5-8 larvae/mL appeared to be optimal for normal S. sub- crenata growth. Larval survival rate decreased with increased stocking density, and survival rate was 35% in the 20 larvae/mL group（P〈0.05）. Larvae reared at 8 larvae/mL exhibited comparatively higher settlement density than that of the other stocking density groups（P〈0.05）. Comparatively higher settlement density was observed on the lower substrate layer than that on the upper and middle layers （P〈0.05）. Settlement time was prolonged and the size of the settled larvae decreased as stocking density increased （P〈0.05）. Therefore, a stocking density of 5-8 larvae/mL is recommended for large-scale seed production.