The Culture Biology And Technology And Selective Breeding In Manila Clam, Ruditapes Philippinarum

The culture biology and technology and selective breeding in Manila clam, Ruditapes philippinarum have been investigated from May 2002 to May 2005.The main results are following: 1. Biology The biological zeros point (BZP) of gonadal development of stocks from Dalian and Putian are 6.77 oC and 10.99℃ , respectively.The effective accumulative temperature EAT of stocks from Dalian and Putian in different conditioning experiments are 315.21 and 172.79 ℃.d. By indoor artificial conditioning, the spawning occurs one and five months earlier than that in northern and southern China, respectively. Fecundities of two-years-old stocks from Dalian and Putian are 6.5×105 and 1.04×106, respectively. The egg size of two-years-old stocks from Dalian and Putian are 66.1±2.4μm and 71.9±3.1μm, respectively, they are significantly different (P<0.01).The means of shell length and width of D-larvae from Dalian and Putian stocks are 96.1(±5.8)×76.8(±4.5)μm and 107.6(±5.6)×82.9(±4.2)μm, their difference is significant (P<0.01).The daily larval growth of Dalian two-years-old clam is 12.20 ×12.47μm, that of Putian two-years-old clam is 9.63×9.79μm, the farmer is obviously faster than the later (P<0.01).When temperature is higher than 25 oC, the swimming stage of larvae from Dalian two-years-old stock is about10 days, the settling size is 179.9×174.4μm,the duration from settling to metamorphosis is about 10 days, metamorphosis size is 230.0×220.0μm. In the same case, the swimming stage, the settling size, the duration from settling to metamorphosis and metamorphosis size of larvae from Putian two-years-old stock are 5-6 days, 179.9 × 174.4 μm, 4~5 days and 196.7×190.8μm, respectively. 2. Ecology 2.1 pH and ammonia Under conditions of temperatures(25.3±1.3) oC and salinity 29, the suitable pH for hatching state varies form 7.24 to 8.69; the suitable pH for the larvae varies form 7.53 to 8.45, the most one is 7.91; the suitable pH for the juveniles varies form 7.99 to 8.45. At pH 7.86, temperatures 22 oC, the 24hLC50 of total ammonia is 11.83mg/l in the hatching stage; the 96hLC50 of total ammonia to D-larva is 7.74mg/l; the juveniles, whose length is 400~600μm, the 96hLC50 of total ammonia is 38.11 mg/l; Form a commercial point of view, pH is more important to larvae of manilla clam than NH+4-N. 2.2 When fed with Isochrysis or a mixture of chlorella and Isochrysis, larval growth and metamorphosis rates were significantly higher than fed merely with chlorella. Larval growth decreased significantly with increasing larval density. Neither diet nor larval density had a significant effect on larval survival. 2.3 Under semi-shaded and fully-shaded conditions, the growth and survival of the larvae were higher than those reared without shade. A water exchange rate of twice a day at 50% provided best growth and better survival of the larvae during the planktonic stage. Larvae grew significantly faster in the unfiltered water than in the sand-filtered water. 2.4 Using sand as a substrate in the culture system depressed juvenile metamorphosis rates by about 20~40% probably due to its inefficient removal of fecal materials accumulated in the sand substrate. The differences in metamorphosis among clam larvae reared using different types and particle sizes of sand as a substrate were found to be unremarkable. 2.5 the toxicity sequence of six heavy metals to gradation is Hg﹥Cd﹥Pb﹥Zn﹥Cu﹥Cr . The LD50 of 96 h for Hydrargyrum is 0.73mg/l; The LD50 of 48 and 96 h for cadmium are 5.85, 3.66mg/l; The LD50 of 48 and 96 h for lead are 29.51, 14.21mg/l; The LD50 of 48 and 96 h for zinc are 79.43, 15.43mg/l; The LD50 of 48 and 96 h for copper are 565.98, 116.84mg/l; The LD50 of 48 and 96 h for chromium are 219.58, 148.73mg/l. The safe concentrations of these metals are 0.036, 0.183, 0.711, 0.772, 5.842 and 7.436 mg/L. When the organisms were exposed to equitoxic mixtures, synergistic effects have been found in paired mixtures with the exception of Hg~Cd which acts synetgistic and Hg~Cr and Cd~Cr acts antagonistic acti...