环境因子及规格对菲律宾蛤仔幼贝潜沙行为的影响

Effects of environmental factors and clam size on the burrowing behavior of Manila clam Ruditapes philippinarum

作为埋栖型滩涂贝类的典型代表种类,菲律宾蛤仔Ruditapes philippinarum具有很强的潜沙行为。为了进一步了解其生态行为学,在室内实验室条件下,模拟了常见环境因子温度、盐度、p H值以及流速和规格大小对蛤仔幼贝(6—12 mm)潜沙速度的影响。结果表明,温度10—30℃,盐度25—30,p H值在6.0—9.0范围内蛤仔幼贝均能100%潜沙;在试验观察的4—5 h内,盐度由30突变至10时没有蛤仔潜沙,突变至20时有20%—30%潜沙(20℃,庄河蛤仔)或100%潜沙(15℃,福建蛤仔);p H值由8.0突变至10.0时不能潜沙;以暂养海水的温度(15或20℃)、盐度(30)和p H值(8.0)为中心,随着各个指标向两侧突变潜沙时间延长;流速为3、4和5 cm/s时,随流速增大潜沙速度加快;在规格6、9 mm和12 mm的幼贝中,以12 mm潜沙速度最快。若以半数潜沙时间(ET_(50))为判定指标,则适宜潜沙温度为15—20℃,盐度为25—30,p H值为7—9(莆田蛤仔)和8.0(庄河蛤仔)。在适宜条件下,蛤仔幼贝1 min内开始潜沙,3 min内有半数潜沙,5 min便全部潜沙。研究发现环境突变对蛤仔潜沙有明显影响,在天然海区放养蛤仔时应该注意购买地和放养海区温度、盐度和p H值的差异,并且选取10 mm以上幼贝放养效果较好。所得结论对完善菲律宾蛤仔幼贝的行为学及其底播养殖技术提供了有意义的参考。

The Manila clam, Ruditapes philippinarum, which is widely distributed along the coasts of China, is an economically important marine bivalve species in China＇s aquaculture industry. Global production of this species was 3.6 million metric tons in 2010. China is the largest producer of Manila clams, producing approximately 3.0 million metric tons annually, which accounts for about 90% of global production. In this study, the effects of clam size and sudden changes in environmental factors such as temperature, salinity, pH, and water flow rate on the burrowing speed of juvenile clams were studied under laboratory conditions. The burrowing rate of juvenile R. philippinarum was 100% at temperatures of 10-- 30℃, at salinity between 25 and 30, and at pH between 6.0 and 9.0. When salinity was suddenly changed from 30 to 10, 4--5 h into the experiment, burrowing ceased. When salinity was suddenly changed from 30 to 20, burrowing rate declined to 20--30% （T = 20℃ ,Zhuanghe clam） or 100% （T = 15℃, Fujian clam）. There was no burrowing when pH was changed from 8.0 to 10.0. Using seawater （ T = 15 or 20℃, salinity = 30, and pH = 8.0） as a control, burrowing time was prolonged when each variable was changed. Burrowing speed increased as the flow rate was increased from 3 to 4 andthen 5 cm/s. The burrowing speed of 12 mm clams was the fastest among the three different shell sizes of juvenile R. philippinarum tested （6 mm, 9 mm, and 12 mm）. Using ETs0 as an index, the optimum burrowing conditions were： T = 15--20℃, salinity = 25--30,pH = 7--9 （Putian clam） or 8.0 （Zhuanghe clam）. Under these optimum conditions, some juvenile clams started burrowing after 1 min, 50% of the clams started burrowing after 3 min, and all clams began to burrow after 5 min. This study shows that abrupt changes in environmental factors had obvious effects on the burrowing behavior of Manila clams. Therefore, we suggest that it is important to pay attention to differences in environmental variables, such as temperature, salinity, and pH, between the place of purchase and the area where clams are to be reared. In addition, it is advisable to introduce clams to the farm when water flow is moderate and the shell length is more than 10 mm.