Size-based physical properties of hard-shell clam (Mercenaria mercenaria) shell relevant to the design of mechanical processing equipment

The knowledge of physical properties of food products is of fundamental importance for efficient design, dimensioning, manufacturing and operation of different mechanical equipment used in the processing of these products. Clams of different sizes are utilized during processing, thus, all the sizes must be given adequate consideration for efficient processing. This study was conducted to investigate the size-based physical properties of hard-shell clam (Mercenaria mercenaria) shell relevant to the design of mechanical processing equipment. The sizes of the clam shells were identified and categorized as small, medium and large; and its effect on the physical properties were studied. The parameters investigated were length, width, thickness, arithmetic and geometric diameters, surface area, sphericity, aspect ratio, moisture content, bulk and true densities, porosity, clam shell weight, coefficient of static friction and angle of repose. Increase in the length and width of clam shells increased the arithmetic and geometric diameters, and the surface area, but decreased the sphericity and aspect ratio. Moisture content, bulk and true densities, porosity and clam shell weight increased with increase clam shell size. Coefficient of static friction of clam shell was highest on rubber surface and lowest on glass surface, and was positively correlated with size; while angle of repose decreased with size. There was an excellent agreement between the prediction of the normal distribution and the actual distribution of the clam shell sizes. All the parameters were significantly different with respect to clam shell size at p < 0.05, which makes a strong case for the consideration of clam shell size during processing.     

小片与蚌间的关系对珍珠质量的影响

本研究采用褶纹冠蚌同一个体自体外套膜小片育珠,结果珍珠质量明显提高。采用三角帆蚌制取外套膜小片植入褶纹冠蚌。结果珍珠质量极差,大多数蚌产不出珍珠;采用褶纹冠蚌制取外套膜小片植入三角帆蚌,结果三分之一的蚌能得到质量高于褶纹冠蚌,产量高于三角帆蚌的珍珠。作者认为供片蚌和受片蚌间相适关系影响珍珠质量,研究如何提高褶纹冠蚌小片在三角帆蚌体内成珠的比率,在生产上是很有意义的。     

Adding value to live, commercial size soft-shell clams (Mya arenaria L.) in Maine, USA: results from repeated, small-scale, field impoundment trials

The soft-shell clam (Mya arenaria L.) fishery in the state of Maine, USA, is worth $5–10 million annually and is primarily based on the sale of live individuals. More than 80% of the catch is sold for the “steamer clam” market that is highly seasonal due to supply and demand. Prices paid to harvesters for live clams throughout the year increases by as much as 70% during a 4-month period between early spring and late summer. If clams harvested in the spring could be held until late summer, a value-added product could be developed in this fishery. From April to August 1996, at an intertidal and subtidal location in eastern Maine, I tested whether it was biologically feasible to impound commercially harvested clams (shell LENGTH=44–75 mm) at densities between 720 and 850/m² using cages and nets (1.12 m²) to protect animals from predators. Survival was 91.7% (n=12) and 91.6% (n=6) at the intertidal and subtidal site, respectively. There was no discernible shell growth during this period and there was no difference between initial and final clam weights. The methodology was transferred to commercial harvesters in two Maine communities: Wiscasset (1997 and 1998) and Perry (2000). Impounded clams ( =21.8 kg/cage; n=18) lost, on average, 5 kg/cage in 1997 and 1998, whereas no significant net loss in wet weight occurred in cages deployed in 2000 ( =23.2 kg/cage; n=3). Differing harvesting and handling methods of individual clammers, prior to impounding clams, likely explains the variation in weight lost during the impounding periods. The difference in price per live kilogram between the beginning of the impounding period and the August sale date resulted in an average gain of $13.60/cage for clammers in 1997 and 1998 and $57.73/cage in 2000. Simple culture techniques can be used to increase the value of the live harvest of soft-shell clams along the coast of Maine. Clam impoundments may be a way for communities that co-manage the public clam resource with the state's marine resource agency to generate funds to pay for traditional management schemes, as well as enhancement programs that employ hatchery-reared juveniles. In addition, an indirect benefit of clam impoundments might be to create spawner sanctuaries since animals are impounded during the time when gamete release occurs.     

胶州湾移植底播菲律宾蛤仔的生长和死亡特性

2004年5月至2005年4月对胶州湾菲律宾蛤仔（Rudimpes philippinarum）底播增殖区进行了逐月定点采样，将样品带回放于实验室内水族箱暂养，每站随机取样，共对3269个个体进行了基本生物学特性测定，研究了移植底播菲律宾蛤仔的生长、死亡等渔业生物学特性。结果表明，底播增殖菲律宾蛤仔苗种的平均个体质量0．26g、平均壳长11．1mm；底播蛤仔与野生蛤仔在生长规律上基本一致，春末至秋初（4～9月）是其主要生长期；1～3龄期间个体生长速度较快，1～2龄、2～3龄，个体质量分别增长3．88g和4．02g；1～2龄生物量增长最快，2～3龄由于死亡率增大，其生物量增长缓慢；1～3龄蛤仔软体部的生长速度快于贝壳，5～6月是菲律宾蛤仔的繁殖肥育期。根据个体生长特性，3龄为最佳采捕年龄；根据目前的养殖状况，2龄蛤仔已达到商品规格，从生物量上分析，采捕2龄蛤仔收益最高；6月是最佳的捕获时期。蛤仔生长具有明显的季节变化，水温是影响菲律宾蛤仔生长的主要环境因子。[中国水产科学，2006，13（4）：642—649]     

文蛤动态能量收支模型构建、验证与应用

为评估文蛤生态容量,实验根据动态能量收支理论,基于R语言构建了文蛤动态能量收支模型,采用线性与非线性回归法估算模型参数,通过对比围塘环境下文蛤壳长、湿重、软体部湿重的实测值与模拟值验证模型,并应用于模拟黄海海域滩涂区文蛤的生长过程。结果显示,文蛤模型主要参数形状系数、阿伦纽斯温度系数和单位体积结构物质所需能量分别为0.57、9 278 K和2 056 J/cm³;实测与模拟的文蛤壳长、湿重和软体部湿重相关系数R²平均为0.996,模拟值与实测值的平均误差为3.58%;如东沿海区域6月实测文蛤软体部干重为0.48 g,壳长3.12 cm,模型模拟的软体部干重、湿重和壳长分别为0.476 g,6.6 g和3.2 cm。研究表明,实验构建的文蛤动态能量收支模型的准确度较高,可真实地反映出文蛤在自然水域中的生长过程,为评估文蛤生态容纳量及构建文蛤相关的生态系统模型提供科学参考。     

缢蛏选育系F5的生长优势比较及育种效应分析

以6个缢蛏(Sinonovacula constricta)自然群体(浙江象山群体、浙江乐清群体、福建霞浦群体、福建长乐群体、江苏射阳群体和上海崇明群体)为材料,构建基础群体F_0,采用群体选育方法进行多代连续选育(选择强度2.063),比较了选育系F_5与对照群体的生长差异,并估计F_5的选择反应、现实遗传力和遗传获得。结果表明,F_5的卵径及受精率与对照组无显著差异(P0.05),但F_5的变态率、存活率及后期壳长生长明显优于对照组(P0.05);7~360日龄F_5壳长的选择反应、现实遗传力与遗传获得的变化范围分别为0.30~0.78,0.14~0.37和4.83%~42.18%,平均为(0.49±0.06),(0.23±0.08)和(26.49±11.73)%。研究结果表明,对缢蛏的连续多代选育是有效的,可以明显提高其存活能力和主要经济性状。     

不同地理群体菲律宾蛤仔壳形态对体重性状的影响研究

采集我国南北沿海9个地理群体的菲律宾蛤仔(Ruditapes philippinarum),利用通径分析等方法评估各群体形态性状对活体重和软体重的影响。结果显示,各群体壳长、壳高、壳宽和壳厚4 个形态性状对菲律宾蛤仔活体重和软体重的影响存在显著差异。除壳厚外,其他形态性状与活体重和软体重呈显著相关(P < 0.05)。通径分析和决定系数分析显示,大多数群体的壳宽对活体重和软体重的直接作用最大。2个形态比例参数(壳宽/壳长和壳高/壳长)最大值出现在山东莱州群体(0.49和0.74),而最小值出现在大连东港群体(0.42和0.67)。壳厚的变异系数最大(22.74),而壳高的变异系数最小(9.47)。通过检验偏回归系数的显著性,建立了各群体形态性状对软体重的最优回归方程。聚类分析表明,菲律宾蛤仔不同群体未出现明显的地域分布特征,而呈现出不规律的南北交替聚类现象。本研究查明了不同地理群体菲律宾蛤仔壳形态性状对体重性状的影响,为菲律宾蛤仔地理群体的形态判别、种质资源分析和遗传育种研究等提供了重要科学依据。     

Effect of dried algae diets on conditioning and fecundity of Manila clam, Tapes philippinarum (Adams and Reeve)

Abstract The effectiveness of live-algae replacement diets for the conditioning and spawning success of adult Manila clam, Tapes philippinarum (Adams and Reeve), was assessed. Two dried diets were tested: a diet of dried Tetrasetmis suecica (Kylin) Butch, and a mixed diet of dried T. suecica (70%) and dried Cyclotella cryptica Reimann et al. (30%). These diets were compared with three live diets: Skeletonema costatum (Grev.) Cleve, Dunaliella tertiolecta (Butcher) and T. suecica. An unfed group was used as a control. The same ration (dry weight) of food was supplied for all groups at 6% of the dry meat weight per day. The broodstock were conditioned for 7 weeks. After 4 weeks none of the animals was ready to spawn. After 6 weeks all the diets promoted spawning and after 7 weeks the unfed group also spawned. It seems that dried algal diets are effective for conditioning and spawning of Manila clams, as the dry meat weight, condition index and fecundity of broodstock fed these diets were significantly greater than for unfed animals. However, the fecundity and proportion of parental lipid released in the eggs of clams conditioned with dried diets was lower than for the clams conditioned with live algae.     

不同地理群体菲律宾蛤仔表型性状的相关性与通径分析

随机选取繁殖时期的南方群体北方养殖菲律宾蛤仔(SN)、北方土著品种(NN)和南方群体南方养殖蛤仔(SS),测量其壳长(SL)、壳高(SH)、壳宽(SW)、活体质量(mL)、软体质量(mM)和烘干后软体部干质量(mF),采用相关与通径分析方法分析不同地理群体的菲律宾蛤仔表型性状对软体质量的作用效果,为菲律宾蛤仔的选择育种提供理论依据和测度指标。试验结果表明,不同地理群体菲律宾蛤仔的形态学指标无显著差异(P>0.05);不同地理群体各数量性状之间的相关关系均达到极显著水平(P<0.01);决定系数分析表明,不同地理群体菲律宾蛤仔影响软体质量的主要表型性状并不相同,南方群体北方养殖蛤仔群体的壳宽直接作用最大,壳宽通过壳高的间接作用是次要因素;北方土著品种群体壳长是主要因素,壳长通过壳高的间接作用是次要因素;南方群体南方养殖蛤仔群体壳高的直接作用是主要因素,壳长通过壳高的间接作用是次要因素。对通径系数检验不显著的自变量进行删除,利用逐步回归的方法,建立不同地理群体菲律宾蛤仔软体质量的最优回归方程:SN群体,mM1=-4.276+0.211SH+0.116SW;NN群体,mM2=-2.806+0.088SL+0.087SH;SS群体,mM3=-3.101+0.290SH。回归方程分析表明回归关系均达到极显著水平(P<0.01)。     

蛋白酶对文蛤肉水解效果的研究

本文探讨了木瓜蛋白酶、胰蛋白酶、精制中性蛋白酶、酸性蛋白酶、复合蛋白酶和风味蛋白酶等6种蛋白酶对文蛤肉的水解效果,以文蛤肉水解液的水解度、氮收率及水解得率为指标,并对酶解液进行感官鉴评和风味评分,结果表明精制中性蛋白酶、胰蛋白酶和风味蛋白酶为适用于文蛤肉水解的蛋白酶。     

Comparison of Three Culture Methods for the Intensive Culture of Northern Quahog Seed, Mercenaria mercenaria

A number of approaches have been utilized for growing bivalve hatchery seed (1 mm) to a size suitable for field planting (< 8 mm) but few have been directly compared. This study evaluated the growth and survival of northern quahog seed in three different culture systems and two different stocking densities. The three systems were: 1) a stacked-tray unit with downward water flow; 2) traditional upweller culture units with water flowing upward without seed bed expansion; and 3) upweller culture units with water flowing upward at fluidization velocities to provide seed bed expansion. The two stocking densities were 1.0 and 3.0 g whole wet weight clam/cm² respectively. During each trial period the seed clams were fed a 1% daily ration (% dry weight algae per wet weight clam per day) of the cultured diatom Chaetoceros muelleri . After 14 d of culture at the 1.0 g whole wet weight/cm² stocking density, seed clams (4.4 ± 0.6 mm initial shell length) under fluidized-flow condition exhibited better growth (0.54/d), and a greater final shell length (5.9 ± 1.0 mm). At the high density stocking conditions, after 28 d of culture, seed clams (4.2 ± 0.6 mm initial shell length) in the fluidized-flow culture conditions again exhibited better growth rate (0.031/d) and a greater final shell length (6.0 ± 1.0 mm). The preliminary evaluation of fluidized-flow for seed clam culture in land-based nurseries indicates its potential as a suitable alternative to raceway, downwelling, or traditional forced-flow culture methods.     

Growing Giant Clam (Tridacna Derasa) in Aquaculture Effluent

Juvenile giant clams (Hippopus spp. and Tridacna spp.) are highly valuable and popular in the aquarium trade due to their brightly colored mantles with various patterns. Giant clams are unique bivalves in that they possess symbiotic zooxanthellae (Symbiodinium). A previous study by the authors demonstrated the feasibility of culturing giant clams in aquaculture effluent. Among the four species tested (Tridacna derasa, T. gigas, T. maxima, and T. squamosa), T. derasa was the most suitable for culturing in effluent. The present study compared the growth, survivorship, and condition indexes of T. derasa (mean initial shell length about 83mm) cultured in fish culture effluent or seawater for six months. The clams grew significantly faster (1.29 vs. 0.93mm shell length/month) and had marginally significant (p = 0.076) higher survivorship (94.1% vs. 77.7%) than those in control seawater. Total (shell and tissue) and tissue weight indexes (g/mm shell length), and mitotic index (% dividing zooxanthellae) were similar between the treatment and control clams; whereas zooxanthellae density (number of zooxanthellae/g clam tissue) of the clams in the effluent tanks was 2.5 times higher than that in control tanks.     

Origin identification method by multiple trace elemental analysis of short-neck clams produced in Japan, China, and the Republic of Korea

The correlations among the contents of trace elements in the shells of short-neck clams collected from Japan, China, and the Republic of Korea were examined. Origin-specific elemental content patterns were seen in clams originating from Japan, China, and the Republic of Korea. The crushed shells were decomposed with nitric acid–hydrogen peroxide, and the concentrations of ten elements (Li, V, Mn, Co, As, Rb, Mo, Ba, Pb, and U) in the shells were measured by inductively coupled plasma mass spectrometry. Some of the metal concentrations in the samples displayed clear geographical trends. The average concentration of Pb in Japanese clam shells was one-half to one-quarter that seen in Chinese or Korean clams. Average concentrations of As, Rb, and Ba in shells of Japanese origin were one-half those observed in Chinese or Korean clams. Linear discriminant analysis was applied to these analytical data, and four discriminant models were constructed. These discriminant models were able to distinguish the geographic origins of short-neck clams with 80.0–100 % accuracy. In particular, clams of Japanese origin were classified correctly ≥90 % of the time. Therefore, the trace elemental analysis of a short-neck clam shell is useful for identifying the country of origin of the clam.     

Growth of the hard clam Meretrix lusoria in Taiwan

The growth of hard clam Meretrix lusoria in Taiwan was observed as it was grown at six different stocking rates (55, 109, 172, 244, 344 and 455 clams/m²), from November 1979 to September 1980. It was found that the stocking rate had more effect on the increase of the total weight of the clam than on the shell length. Under the environmental condition of the study site, the optimum stocking rate was 244 clams/m². When the net production of the clam was lower than 1103 g/m², the growth of the individual clam was not affected by the stocking rate. But when the net production was higher than 1589 g/m², the growth of the individual clam seemed to be retarded. The average pH of the sea water in the clam culture area was between 7.9 and 8.4. The average dissolved oxygen content was between 4.2 and 11.2 mg/l. And the average water salinity was between 30‰ and 35‰. All these three factors did not seem to have direct relationship with the growth of the clams. Sea water temperature, however, showed great effects on the growth of the clams. It is shown that the growth of the hard clam was slow at a water temperature of 15–18°C, increased at 20–22°C, and accelerated at 25–32°C.     

SEM observations on larval shell morphology of Manila clam Ruditapes philippinarum and their utility

Manila clam Ruditapes philippinarum is common and abundant on Japanese tidal flats, forming a commercially important clam fishery. However, annual catches of Manila clam have decreased drastically since 1975?C1985. To study larval recruitment processes of Manila clam, we carried out scanning electron microscopy (SEM) observations on larval and juvenile shells of clams reared at 20 and 24?°C. There was no significant difference in final shell length of trochophores between 20 and 24?°C. However, the larval duration was much longer and the shell length of settled size of pediveligers was much larger for clams reared at 20?°C than those reared at 24?°C. These findings suggest that larval duration and growth, as well as settlement size, may vary markedly depending on temperature (and probably on season). The larval shell morphology of Manila clam can provide essential information about larval recruitment processes.     

文蛤年龄的研究

本文采用透光法鉴定文蛤的年龄．当贝壳在光透射下，条纹清晰显出。贝壳的亮带形成是在5月至10月，暗带则在10月至翌年的5月间形成。不同年龄组的亮带和暗带形成的时间没有差别。通过贝壳的亮、暗分界线，可以判断文蛤的年龄。     

Mariculture of giant clams,Tridacna crocea and T. derasa: Management for maximum profit by smallholders in Solomon Islands

Abstract

The International Center for Living Aquatic Resources Management (ICLARM) has demonstrated that coastal village communities in Solomon Islands can successfully farm giant clams. The production technology is simple and does not require a large capital investment. The main inputs are clam seed, labour and time. Labour is used for activities such as planting, cleaning, thinning and harvesting. In this paper, a bioeconomic model is used to explore optimal farm management for two species of giant clam fanned for the aquarium and seafood markets. The theoretical basis for this analysis is found in the economic theory of optimal forestry exploitation. Optimal management involves finding the combination of the decision variables and the cycle‐length that maximises a stream of discounted profits. The decision variables considered here are husbandry which relates to cleaning, and the frequency with which thinning is undertaken. The optimal cycle‐length is determined for both a single‐clam harvest and multiple harvests for various management scenarios. The labour requirements for these management scenarios are identified for the multiple‐harvest case and input substitution between optimal combinations of labour and cycle‐length is investigated. Results indicate that profits are maximised for both species when husbandry is excellent and labour usage is most intensive. Thinning is only necessary for seafood clams for which the optimal cycle‐length is longer. Village farmers may not be profit maximisers however, and labour spent on giant‐clam farming takes them away from other activities. Rather than investing more labour and harvesting the clams earlier, a village farmer with other objectives may devote less labour and harvest the clams later, and spend more time on other activities. In general, these results are consistent with extension advice provided to village farmers by ICLARM. Optimal solutions were found to be very stable when incorporated into global optimisation routines and sensitivity analysis of a wide range of parameter values.     

四角蛤蜊形态性状对重量性状的影响效果分析

以随机选取的123只野生四角蛤蜊为材料,对其形态性状(壳长X₁、壳高X₂、壳宽X₃)和重量性状(活体质量Y、软体质量Z)进行了测量,然后运用相关分析、通径分析和回归分析等分析方法研究形态性状对重量性状的影响。结果表明,5个数量性状间的相关系数均达到极显著水平(P<0.01)。形态性状对活体质量和软体质量的直接影响依次为壳宽>壳长>壳高。壳宽是影响活体质量和软体质量的主要因素,其决定系数分别为0.302 5和0.224 7。多元回归分析建立了估计活体质量、软体质量的最优回归方程:Y=-19.537+0.244X₁+0.266X₂+0.732X₃、Z=-2.456+0.035X₁+0.035X₂+0.089X₃。     

Culture of Juvenile Atlantic Surfclams, Spisula solidissima solidissima and Spisula solidissima similis, in Forced-Flow Upwellers in a Bivalve Hatchery in Coastal Georgia

Four experimental growth studies for juvenile Atlantic surfclams, Spisula solidissima solidissima and Spisula solidissima similis , under hatchery conditions were conducted in 10-cm diameter forced-flow upweller units. Experiments were designed to determine optimum food ration (2%, 5%, and 8% g dry weight of algae/g wet weight of clam), water culture temperature (20, 25, and 30°C), flow rate (2, 4, and 6 Lpm), and stocking density (7, 14, and 21 g wet weight of clams) for rearing juvenile clams in upweller units. Each experimental trial was performed for a 14-d period. Nested Analysis of Variance showed that juvenile surfclams Spisula solidissima similis grew significantly faster at a temperature of 20°C and food rations of 5 % and 8%. In all four experiments, clam mortalities were not observed except in the temperature experiment, where total mortality occurred for clams cultured at 30°C. Clam growth in biomass and size decreased significantly with increases in culture temperature. For Spisula solidissima solidissima , clam growth was significantly reduced in terms of size and biomass at a flow rate of 6 Lpm. No difference in size or biomass was determined between clams grown at a flow rate of 2 or 4 Lpm. Surfclams at the lowest stocking density of 7 g wet weight significantly increased more in net biomass compared to those at higher stocking densities. Clams were significantly larger in shell length when grown at the two lower stocking densities compared to those at the highest stocking density. Hatchery-rearing protocol for juvenile surfclams is discussed.