蛤蜊的“奥运会”

“蛤了，蛤了——”是谁在唱歌？哦，原亲是一只只肥嘟嘟的蛤（ge）蜊（li）在跳减肥操。“一二三四肥肉下去，二二三四肥肉下去……”蛤蜊一个个慢慢地露出大嘴巴，伸出乳白色的舌头。只见，一粒粒细沙慢慢地从它们嘴里吐出来。更有趣的是，它们三个一群，五个一伙，

Seasonal Variation of Biochemical Components in Clam (Saxidomuspurpuratus Sowerby 1852) in Relation to Its Reproductive Cycle and the Environmental Condition of Sanggou Bay, China

Seasonal variation of biochemical components in clam(Saxidomus purpuratus Sowerby 1852) was investigated from March 2012 to February 2013 in relation to environmental condition of Sanggou Bay and the reproductive cycle of clam.According to the histological analysis,the reproductive cycle of S.purpuratus includes two distinctive phases:a total spent and inactive stage from November to January,and a gametogenesis stage,including ripeness and spawning,during the rest of the year.Gametes were generated at a low temperature(2.1℃) in February.Spawning took place once a year from June to October.The massive spawning occurred in August when the highest water temperature and chlorophyll a level could be observed.The key biochemical components(glycogen,protein and lipid) in five tissues(gonad,foot,mantle,siphon and adductor muscle) were analyzed.The glycogen content was high before gametogenesis,and decreased significantly during the gonad development in the gonad,mantle and foot of both females and males,suggesting that glycogen was an important energy source for gonad development.The protein and lipid contents increased in the ovary during the gonad development,demonstrating that they are the major organic components of oocytes.The lipid and protein contents decreased in the testis,implying that they can provide energy and material for spermatogenesis.The results also showed that protein stored in the mantle and foot could support the reproduction after the glycogen was depleted.

Enzyme responses and lipid peroxidation in gills and hepatopancreas of clam Mactra vereformis, following cadmium exposure

To assess the toxicity of heavy metal pollution to marine intertidal shellfish, enzymatic responses and lipid peroxidation were investigated in the clam Mactra vereformis exposed to cadmium under laboratory conditions. Three antioxidant enzymes (superoxide dismutase, SOD; catalase, CAT; glutathione peroxidase, GPx), two immune defense enzymes (acid phosphatase, ACP; alkaline phosphatase, ALP), and one lipid peroxidation product (malondialdehyde, MDA) were measured in the gills and the hepatopancreas of the clam exposed to 0, 25, 75, and 125 μg/L cadmium for 0, 1, 3, 5, and 7 d. The results show that the concentrations of antioxidant enzymes in the organs soared to a peak value on the first day and then decreased afterwards in most cases. CAT and GPx activities in the hepatopancreas were higher than in the gills, but the SOD activity was lower in the hepatopancreas. ACP activity was unchanged until Day 3 in the hepatopancreas and until Day 5 in gills, when it began to increase. ALP activity showed no significant relationship with Cd treatment. MDA concentrations increased in the two tissues after Cd exposure, peaked on Day 3 in gills, and on Day 5 in hepatopancreas. These observations show that changes in the activities of antioxidant enzymes and ACP reflect the time course of oxidative stress in the clam caused by Cd, and could be used as potential biomarkers for ecotoxicological bioassays of heavy metals.

An Efficient Method of Noroviruses Recovery from Oysters and Clams

Noroviruses (NoVs) are widespread causes of nonbacterial gastroenteritis. Outbreaks of NoVs caused diseases are commonly ascribed to the consumption of contaminated shellfish. The concentration and RNA extraction of NoVs are crucial steps of detecting NoVs in shellfish. This study aimed to select a simple, rapid and highly efficient recovery method of NoVs detection with real-time RT-PCR. Four methods of recovering GI.3 and GII.4 NoVs from spiked digestive tissues of oysters and clams, respectively, were compared, of them, the method involving proteinase K and PEG 8000 was found the most efficient. With this method, 9.3% and 13.1% of GI.3 and GII.4 NoVs were recovered from oysters and 9.6% and 12.3% of GI.3 and GII.4 NoVs were recovered from clams, respectively. This method was further used to detect NoVs in 84 oysters (Crassostrea gigas) and 86 clams (Ruditapes philippinarum) collected from 10 coastal cities in China from Jan. 2011 to Feb. 2012. The NoVs isolation rates were 10.47% of clams (9/86) and 7.14% of oysters (6/84). All the detected NoVs belonged to genotype GII. The NoVs recovery method selected is efficient for NoVs detection in oysters and clams.

Effects of clam size, food type, sediment characteristic, and seawater carbonate chemistry on grazing capacity of Venus clam Cyclina sinensis (Gmelin, 1791)

Aquaculture in saline-alkaline water has a major problem： microalgal blooming causes the pH of water to increase dramatically, thereby causing damage to the reared organisms. To solve this problem, we set out to find a candidate filter-feeding bivalve species suitable for saline-alkaline water to graze on microalgae and to control the pH. In the current study, we investigated the effect of carbonate alkalinity （CA, 2.5, 10.0, and 20.0 meq/L） and pH （8.0, 8.5, and 9.0） on the grazing capacity （GC） of the clam Cyclina sinensis. Additionally, the effect of clam size （small, medium, and large） and microalgae species （Nannochloropsis oculata, Chaetoceros miielleri, and lsochrysis galbana）, and the effect of bottom sediment characteristic （mud, sandy mud, and muddy sand） and thickness （3 and 6 cm） were analyzed as well. The results show that the GC on L galbana was the highest and small size had the maximum GC/W （W： wet weight including body and shells）. No significant differences were observed between sediment type and thickness. Regarding CA and pH, a significant decrease in GC by the pH or by their interaction was found. The GC ofC. sinensis was not greatly reduced in the treatments ofpH≤8.5 and CA≤20.0, and also not affected by bottom sediment type, indicating that this clam is capable to manage microalgal concentrations and might be a candidate species for pH reduction in saline-alkaline water ponds.

A Novel Hydrolytic Product from Flesh of Mactra veneriformis and Its Bioactivities in Calcium Supplement

To prepare calcium-binding peptides, the flesh residue of Mactra Veneriformis was subjected to enzymatic hydrolysis. By comparing the capability of combining calcium of the hydrolyzates, pepsin was confirmed to be the most suitable enzyme for hydrolyzing the flesh residue to release calcium-binding peptides among the seven tested proteases. The pepsin hydrolyzate (PHM) was divided into three fractions according to the molecule weight of its composition, which ranged from 0.5 to 15 kDa. The low-molecule-weight fraction named PHM-3 had the highest capability in combining calcium. The peptides existing in the PHM-3 fraction consisted of higher contents of Glu, Ala and Leu, and could produce one type of calcium-peptide complex by powerfully chelating calcium ions. PHM-3 products could effectively increase calcium absorption and retention while they decreased the calcium excretion in animal tests. Additionally, symptoms caused by low calcium bioavailability in ovariectomized rats, such as bone mineral density reduction and mechanical strength loss could be significantly ameliorated by the hydrolytic products addition in diet.

Experimental investigation of clam water impact on flatted-bottom seafloor mining tool

A test rig for constant velocity water entry experiments was developed that drives a flatted-bottom section attached on six degree of freedom(6-DOF) platform to enter the water vertically at near constant velocity.The experiment system,which consists of drive and actuation system,water pool,model test sections,load cell,and control system,was presented.Water entry forces of different velocities were measured during impact process,and for each test case,three runs were performed with the same motion program to check the repeatability of the force readings.The experiment results are compared with two-dimensional(2D) CFD simulation methods for flatted-bottom rigid bodies with constant entry velocity.Experimental results indicate that the impact forces mainly depend on water entry velocities.It is concluded that the feasibility and accuracy of simulation methods has been validated.

蛤蜊

我买了一斤蛤蜊,有一只,在我清洗时,咬住了我筷子,吓了我一跳,头一次,我意识到,它们也是活生生的,还在活着。炒完蛤蜊,只有一只没有张口,紧紧闭着,我觉得,就是那一只。