Characterization of haemocytes of the Indian edible oyster, Crassostrea madrasensis (Preston)

The haemocytes of the Indian edible oyster Crassostrea madrasensis were characterized using light and electron microscopy. The light microscopic study was conducted by staining a monolayer of the haemocytes with Geimsa. Cells without granules and with a large nucleus occupying much of the cytoplasmic area were grouped as hyalinocytes. Those with lesser amounts of basophilic cytoplasmic granules were characterized as semigranulocytes and those with large amounts of a mixture of acidophilic and basophilic granules were termed as granulocytes. Ultrastructural studies also revealed the presence of three types of haemocytes. Scanning electron microscopic studies were used to study the spreading behaviour of the haemocytes. Cytochemical studies revealed the presence of acidphosphatase, peroxidase and prophenol oxidase in the cells.     

Mud blister formation by Polydora ciliata in the Indian backwater oyster Crassostrea madrasensis (Preston)

The mud blister formation by Polydora ciliata in the Indian backwater oyster Crassostrea madrasensis (Preston) is described. The nature of attack of P. ciliata is compared with that of P. Websteri. P. ciliata, however, does not inflict serious injuries to the oyster. It is observed that the lowering of salinity to almost freshwater condition, due to monsoon rains, causes considerable damage to the polychaete population in the estuary.     

栉孔扇贝雄核发育二倍体的人工诱导

研究了利用6-二甲基氨基嘌呤(60μg/mL;6-DMAP)抑制第1卵裂诱导栉孔扇贝[Chlamys farreri(Jones et Pre-ston)]雄核发育二倍体的条件。雄核发育单倍体是将强度为2.8 mW/(cm2.s)的紫外线照射20 s的卵子与正常精子受精后得到的。6-DMAP不仅可以有效地抑制减数分裂,还可以有效地抑制有丝分裂;抑制第1卵裂的适宜起始时间为受精后80 min,诱导率为21.0%~22.6%。细胞学观察显示,6-DMAP抑制第1卵裂产生的雄核发育二倍体主要来源于第1卵裂中期的受精卵,由于阻止了染色体分离和原核移动,导致一个融合的二倍性雌性原核的形成;经紫外线照射的卵核在第1卵裂中期没能形成染色体,而是形成1个浓缩的染色质小体,没有参与第1卵裂后期的核分裂。尽管倍化率和D形幼虫发生率较低,但本研究证实了栉孔扇贝雄核发育二倍体人工诱导的可行性。[中国水产科学,2006,13(4):585-590]     

The reproductive biology of the Indian oyster Crassostrea madrasensis (Preston): II. Gametogenic cycle and biochemical levels

Changes in the biochemical levels of the adductor muscle, mantle and gonad during the fist gametogenic cycle of Crassostrea madrasensis (Preston) indicate a major conversion of reserve nutrients (carbohydrate and lipid) into gamete material. The main reserve nutrient, carbohydrate, is stored primarily in the gonad before the commencement of the first gametogenic cycle. It is inferred that the development of the gonad in the second gametogenic cycle is directly dependent on the nutrients derived from food sources.     

微卫星标记在长牡蛎三倍体鉴定中的应用

为开发一种简单有效的倍性检测方法对长牡蛎三倍体诱导结果进行准确评估,本实验采用细胞松弛素B抑制第二极体释放诱导产生长牡蛎三倍体,选用7个微卫星位点扩增基因组DNA,通过亲子代基因分型进行倍性检测,检测结果采用流式细胞仪加以验证,以评估微卫星标记倍性检测的准确性。另外,本研究探讨了准确鉴定倍性所需的微卫星标记数量与微卫星—着丝粒重组率(y)之间的关系,以期为其他物种采用分子标记进行倍性检测提供理论依据。结果显示,细胞松弛素B诱导产生的115个长牡蛎子代经7个微卫星位点鉴定得到40个三倍体,与流式细胞仪检测结果一致,准确率达到100%,7个微卫星位点的(1-y)的乘积为0.005。随机挑选6个位点,也可鉴定出所有三倍体,(1-y)的乘积为0.005~0.042。研究表明,本研究中开发的微卫星标记可以简单高效地鉴定长牡蛎三倍体,微卫星位点的(1-y)的乘积小于0.005,倍性检测的准确率可达100%,采用微卫星标记进行倍性检测对于加速长牡蛎三倍体育种进程具有十分重要的意义。     

Reproduction, condition and mortality of the Pacific oyster Crassostrea gigas (Thunberg) in Sonora, México

Starting in 1997, mortality outbreaks in cultured oysters Crassostrea gigas have been reported in northwestern México. Previous studies have shown that massive die‐offs result from multi‐factor processes related to reproduction of the species. We studied the reproductive cycle and the condition index of cultured oysters in the coastal lagoon of El Soldado, Sonora, as well as the relationship of the life cycle with environmental parameters. We used oocyte diameter to determine reproductive stages and the condition index to describe the physiological state of oysters. Additionally, the temperature, salinity, seston and chlorophyll a were recorded at the study site. The results showed that C. gigas began accelerated reproductive activity in March under the influence of high temperature and increased concentrations of food. No spawning events were recorded and gametes were reabsorbed within the gonad in September and October. The results showed a period of nutrient storage during autumn–winter and another period of gamete production in spring–summer. A mortality event occurred at the end of winter, tied to significant increases in temperature and availability of food and in accelerated reproductive activity and high condition index. These conditions were very similar to those reported in other countries during summer die‐offs of C. gigas.     

5种壳色长牡蛎不同组织常规营养成分分析与评价

对壳黑、壳紫、壳橙、壳金和壳白5种壳色长牡蛎(Crassostrea gigas)不同组织包括闭壳肌、外套膜、鳃、性腺-内脏团的营养成分(水分、总蛋白质、总脂肪、糖原、灰分)进行检测分析,比较它们与普通养殖群体营养成分的差异以及5种壳色长牡蛎各组织间营养成分的差异。结果表明,在闭壳肌中,壳紫长牡蛎的总脂肪含量显著高于壳橙长牡蛎(P0.05),其他组分在6个群体中未表现出显著性差异(P0.05);在外套膜中,壳金长牡蛎总脂肪含量显著高于壳黑、壳橙和普通养殖群体(P0.05),壳白长牡蛎的灰分含量显著高于普通养殖群体(P0.05),其他组分在各群体之间未表现出显著性差异(P0.05);在鳃中,长牡蛎壳橙、壳紫、壳白选育群体的糖原含量显著低于对照组(P0.05),其他组分在6个群体之间没有显著性差异(P0.05)。长牡蛎5种壳色选育群体和普通养殖群体的性腺-内脏团在水分、总蛋白质、总脂肪、糖原和灰分中均无显著性差异(P0.05)。4个组织中水分和灰分均以外套膜和鳃中含量最高,闭壳肌中总蛋白质的含量则在4个组织中居首位,总脂肪和糖原含量均以性腺-内脏团中最高。研究结果表明不同壳色长牡蛎之间以及不同壳色与普通对照群体之间在一些重要营养成分上已表现出分化,这为长牡蛎壳色品系选育提供了重要的参考资料。     

Growth of the oyster Crassostrea corteziensis (Hertlein, 1951) in Sonora, Mexico

This is the first evaluation of growth and survival of spat of the Cortez oyster Crassostrea corteziensis (Hertlein) produced under controlled conditions in a coastal area in the state of Sonora, Mexico for aquaculture purposes. A suspended culture technique, used for the Pacific oyster C. gigas, was used. The Cortez oyster has an isometric shell growth during the first 13 months, reaching 71.3±1.9 mm length, 52.6±1.3 mm thickness and 25.1±0.8 mm width. Allometric growth was found between total weight and length, thickness and width (survival was 70%). The relationships between particulate organic, inorganic material, chlorophyll a and environmental parameters with growth are described. Growth rates of C. corteziensis were affected by temperature with retardation at less than 18°C. For aquaculture purposes, it is recommended that spat be sowed after winter, and oyster harvest occur at the end of autumn. According to the von Bertalanffy equation, Cortez oysters would reach the traditional exploitation size of 65 mm (mean length) at harvest. Finally, the results of this study have shown that C. corteziensis is a good candidate for aquaculture projects in this region.     

Sex-specific growth and condition of the Pacific oyster (Crassostrea gigas Thunberg)

In order to study the possibility of gaining commercial benefit from culturing an excess of one sex of the Pacific oyster (Crassostrea gigas), comparative data on the growth rate and condition of male and female oysters are reported. Historically, measurement of sex‐specific growth rate in oysters has been overlooked or confounded by protandric sex. The recent conclusion that the sex ratio of Pacific oysters is predominantly under genetic rather than environmental control introduces the possibility of manipulating sex ratio for commercial gain if they exhibit asynchronous sex‐specific growth rates. Pacific oysters were cultured intertidally in Smoky Bay, south Australia. The observations, made over the 7‐month gametogenic cycle from August to February to ensure no sex reversal, were of growth rates of male and female oysters and ambient chlorophyll a concentrations. Mean shell growth of female oysters was significantly faster than that of males (4.5 ± 3.3 compared with 3.8 ± 3.2 μm day^?1 mm^?1 total length). Sex‐specific asymmetries in length and weight were generally significant and increased in magnitude during the 7‐month study period, suggesting potential commercial benefits from increasing the proportion of cultured female oysters. The fastest increase in the sex‐specific disparity in growth and condition came after the October chlorophyll a peak, suggesting that females utilize blooms more efficiently than males. Our results compare favourably with methods currently used to increase oyster growth (e.g. triploidy can provide growth gains of 13–51%).     

Growth and feeding in juvenile triploid and diploid blacklip abalone, Haliotis rubra (Leach, 1814), at two temperatures

Growth and feeding of juvenile triploid and diploid blacklip abalone Haliotis rubra (Leach, 1814) were investigated at two temperatures of 17 and 21 °C over a 50‐day period. There were no differences in growth between triploid and diploid abalone as measured by shell length and body weight. Both triploid and diploid abalone increased in length but not in weight at 21 °C. Condition indices were similar for triploid abalone maintained at both temperatures; however, those for diploid abalone were significantly higher at 17 °C than at 21 °C. Food intake was significantly greater yet feed conversion efficiency was significantly lower in triploid than in diploid abalone. Both the feeding variables were independent of temperature. On average, diploid abalone were able to convert 1 g of dry food ingested to 0.58 g of body weight, but triploid abalone only 0.44 g.     

Seasonal variations in the immunological and physiological parameters of the Pacific oyster Crassostrea gigas cultured in Bahía de Macapule (Sinaloa,Mexico)

Triploid Crassostrea gigas were cultured during 13 months in Nestier‐type oyster trays. The impact of environmental parameters on the physiological and immunological parameters was evaluated. Temperature, salinity and seston were recorded monthly. Seventeen oysters were sampled monthly for immunological and condition index (CI) analyses. Samples were obtained as a haemolymph lysate supernatant (HLS). Protein content was determined using the Bradford method. The activity of hydrolytic enzymes was determined using the API ZYM kit and the lysoplate assay. Seston showed different patterns throughout the cycle. Condition index showed a positive correlation with the protein content of HLS. Protein showed a negative correlation with temperature. Eleven hydrolytic enzymes were detected in samples and higher enzymatic activity corresponded to leucine arylamidase and esterase. Leucine arylamidase and lysozyme activity showed a positive correlation with temperature. Oyster mortality was 28% in our modules and 70% in the oyster farm. Oysters showed low values of CI and haemolymph protein content in summer–autumn when mortalities were observed in the culture system. This finding suggests that these stressed oysters may have insufficient energy to invest in their immune system. It appears that oyster mortality in the culture system resulted from a combination of animal overcrowding, high temperature and low salinity.     

Seasonal variation in the condition index of Pacific oyster postlarvae (Crassostrea gigas) in a land‐based nursery in Sonora,Mexico

This study examined the seasonal variation in the condition index (CI) of Crassostrea gigas postlarvae (<5 mm) that were cultivated at a commercial hatchery. Oysters were sampled weekly at the nursery using seawater from a lagoon for the grow‐out that precedes commercialization. Temperature, salinity, seston, chlorophyll a, oxygen and pH were recorded at each sampling and water samples were taken to identify phytoplankton groups and their abundance. High levels of primary productivity, chlorophyll a and seston were detected during summer, but the highest CI occurred in winter. During winter, elevated phytoplankton biomass was composed by diatoms and phytoflagellates, which served as the main food source and promoted weight gain in this season. Variations in salinity, oxygen and pH were not related to differences in the CI. However, it appears that the wide temperature variation affected functions, such as feeding activity, apparently enhancing ingestion during winter (mean 16.5±1.4 °C) and reducing ingestion during summer (mean 31±1.5 °C). Winter production resulted in postlarvae with a homogeneous size range and a high CI, indicating that winter is more favourable to start cultivation. The CI represents a practical means to determine the physiological state of postlarvae before transfer to cultivation sites.     

Studies on triploid oysters in Australia: farming potential of all-triploid Pacific oysters, Crassostrea gigas (Thunberg), in Port Stephens, New South Wales, Australia

Triploid Pacific oysters Crassostrea gigas farmed in Port Stephens, NSW had an exceptionally fast growth rate and reached a whole weight of 55 g in 13 months versus 20 months for diploids. Mortality of the triploids (24.5±2.94%) was significantly lower (P<0.05) than that of the diploids (40.0±2.26%) over the duration of the experiment (July 2002–February 2004). Unfortunately, this advantage was offset by discoloration of the meats of the triploids when they were in better condition than the diploids over summer (October 2003–March 2004). However, discoloration of meat of triploids had cleared up by April 2004 and neither did they suffer this problem from April–September 2003. The triploids also had a lower peak condition than the diploids. Oysters in peak meat condition, i.e. spawning condition, are preferred for the half shell trade in Australia and in this study, there was at least a six‐month period prior to discoloration, when the triploids were large enough and had sufficient meat condition for marketing on the half shell.     

Optimization of triploid induction by the use of 6-DMAP for the oyster Crassostrea gigas (Thunberg)

Abstract. A novel method using 6-dimethylaminopurine (6-DMAP) has recently been demonstrated to be a good triploid inductor for bivalve molluscs. The effects of 6-DMAP concentration, timing of treatment after fertilization, and treatment duration on survival and triploid induction of Crassostrea gigas (Thunberg) embryos were examined. An influence of sperm concentration was also detected and discussed. Survival to D-stage was inversely related to 6-DMAP concentration and the percentage of triploids was shown to be 6-DMAP dose dependent. Two optimal moments for treatment application were determined, corresponding to extrusions of the first and second polar bodies. Optimal treatment of 450μmol/1 6-DMAP beginning 15min after fertilization over a 10min period yielded mean survival to D-stage of 64% with a mean of 85% triploid production. As a comparison, a sample treated with 1 mg/1 of cytochalasin B (CB), 20 min after fertilization over a 15 min period, yielded a mean survival to D-stage of only 36% with a mean of 95% triploid production. The advantages of 6-DMAP over CB are clearly identified: this chemical is not carcinogenic, cheaper than cytochalasin B and much easier to use as it is water soluble.     

夏季高温期三倍体和二倍体长牡蛎生理能量学及碳收支的比较研究

为解析夏季高温期三倍体与二倍体长牡蛎(Crassostrea gigas)摄食和代谢生理以及能量/碳分配策略的差异,于2022年8月,以三倍体和二倍体长牡蛎为研究对象,在山东荣成桑沟湾采用现场流水法测定滤水率、吸收效率、耗氧率、排氨率等摄食和代谢相关生理参数,并基于能量收支方程估算能量分配与碳分配情况。结果显示,三倍体长牡蛎的滤水率、同化效率均高于二倍体长牡蛎,但无显著差异(P>0.05);三倍体与二倍体长牡蛎的耗氧率、排氨率存在显著差异(P<0.05),三倍体长牡蛎的耗氧率显著低于二倍体长牡蛎(P<0.05),但排氨率显著高于二倍体长牡蛎(P<0.01)。能量收支与碳收支的结果显示,三倍体长牡蛎的摄食能/碳、同化能/碳均高于二倍体长牡蛎,但无显著差异(P>0.05);三倍体与二倍体长牡蛎的呼吸能/碳、排泄能/碳、生长余力存在显著差异(P<0.05),三倍体长牡蛎的呼吸能/碳显著低于二倍体长牡蛎(P<0.05),但排泄能/碳、生长余力显著高于二倍体长牡蛎(P<0.05)。三倍体和二倍体长牡蛎的氧氮比波动范围分别为7.91~14.11和59.81~94.19,因此,三倍体长牡蛎的主要供能物质为蛋白质,二倍体长牡蛎的主要供能物质为糖类和脂肪。研究结果为揭示夏季高温期长牡蛎倍性效应关联的能量分配方式差异提供了数据支撑。     

Comparative studies of the growth,survival, and reproduction of diploid and triploid Kumamoto oyster,Crassostrea sikamea

Triploid oysters have been used for farming to improve growth but have not been created in the Kumamoto oyster, Crassostrea sikamea, which is one of the crucial aquaculture species on the southern coast of China. In the present study, triploids were created using cytochalasin B to inhibit polar body II release in C. sikamea, with the untreated oysters as controls. Triploidy rates of 87 and 57.67%, on average, were obtained in larvae and adults, respectively. Larval growth and survival of the triploid were significantly lower than that of the controls (p < 0.05). In contrast, the triploid postlarvae and adults had a significant growth advantage over the controls (p < 0.05) during the period of 180 (December) to 450 days (September of the next year). Moreover, the triploids clearly exhibited significant sterility in the reproductive season. The glycogen and triglyceride contents in the gonad, adductor muscle, mantle, and gill were higher in triploids than in controls from 180 to 450 days. As a result, high physiological energy supply was strongly correlated with superior growth and reduced reproduction in triploid C. sikamea. The triploid C. sikamea is an excellent oyster species and can be used to improve growth for C. sikamea farming.     

Growth,mortality and reproductive traits of diploid and triploid Pacific oysters (Crassostrea gigas,THUNBERG, 1793) in Southern Brazil

This work aimed to evaluate the whole weight (g), shell height (mm), mortality (%) and reproductive aspects (condition index and histology) of triploid (3N) Pacific oysters (Crassostrea gigas) cultivated in southern Brazil. To accomplish this, a comparative experiment was performed with a diploid (2N) control group in two cultivation sites on Santa Catarina Island: North Bay (NB) and South Bay (SB). Whole weight, height and cumulative mortality were evaluated monthly for eight months and condition index (CI) for six months. Histological analysis was performed every two weeks for four months to investigate reproductive aspects. At the end of the experiment, whole weight and height were similar for 3N and 2N oysters. However, while more growth in whole weight and height was observed in the initial phase of cultivation in NB, such growth was not detected in SB until intermediate and final grow‐out phase. At harvest, cumulative mortality in 3N oysters was similar that in 2N oysters. The results suggest that diploid and triploid oysters grown in southern Brazil have similar developmental patterns based on whole weight and height, as well as reproductive cycle. In addition, cultivation sites have more influence on growth and mortality than ploidy levels.     

葡萄牙牡蛎的净化及其低温贮藏研究

为保证生食葡萄牙牡蛎(Crassostrea angulata)的安全,在贝水比1∶10、水交换率3次/h、水温28℃、盐度28的条件下,采用流水式紫外线杀菌方法净化48 h,检测净化前后13个卫生指标的变化;净化后的牡蛎在冷藏(4℃)和冷冻(-18℃)两种条件下贮藏7 d以上;检测贮藏过程中菌落总数、大肠菌群和主要营养成分的变化。结果显示,经过48 h净化,菌落总数和大肠菌群含量均大幅下降,重金属、化学污染物等指标变化不大;两种贮藏条件下,菌落总数和大肠菌群都呈先下降再上升的变化,但始终处于安全水平内;蛋白质、脂肪、糖原含量缓慢下降,乳酸含量快速上升。研究表明,葡萄牙牡蛎在紫外线杀菌净化48 h后,至少在冷藏6 d或冷冻11 d内可以保证食品安全。     

基于微卫星标记整合长牡蛎遗传图谱

为了提高长牡蛎遗传图谱上的微卫星标记密度,实验采用6个家系图谱间的共有微卫星标记作为锚定标记,构建了长牡蛎的整合图谱.该整合图谱共有161个微卫星标记,覆盖10个连锁群,图谱长度和平均间距分别为615.4和3.8 cM.各连锁群的标记数介于10 ～ 24个之间,连锁群长度为47.3～73.3 cM,是目前密度最高的长牡蛎微卫星图谱.不同作图家系连锁群上的标记分组保持一致,但标记顺序出现差异,可能与长牡蛎自然群体中存在大量的染色体重排现象有关.结果表明,该图谱可以为今后长牡蛎的遗传育种研究提供新的遗传工具.     

A comparative study of the survival,growth and gonad development of the diploid and triploid Hong Kong oyster,Crassostrea hongkongensis (Lam & Morton 2003)

The Hong Kong oyster, Crassostrea hongkongensis is an economically important and widely cultivated oyster species in southern China. Aiming to improve the aquaculture potentials of C. hongkongensis, a triploid organism was generated by inhibiting the second polar body formation in the fertilized eggs, using 0.5 mg L^?1 cytochalasin B. Triploids exhibited significantly higher growth and were larger than the diploids throughout the life cycle. Much of the triploid growth advantage can be attributed to resource reallocation to structural development due to gonadal sterility. Most of the triploid oysters exhibited polymorphic sterility with atrophic gonads and abnormal gametogenesis. Only few ‘dysfunctional’ sperms were produced by the triploid males, thus ruling out reproductive and genetic contamination of natural oyster populations from triploid cultivations. This advantage in addition to the superior growth of triploids makes it a potent alternative in Hong Kong oyster aquaculture industry. Triploid survival was mostly found to be similar to that of diploids except for day 360, when a significant triploid advantage in terms of survival was noted. Furthermore, we found that growth and survival of Hong Kong oyster is significantly higher at the Zhuhai site in comparison to the Beihai site. Our results indicate a strong environmental effect in Hong Kong oyster cultivation and points to the fact that Zhuhai site was more suitable for oyster farming than the Beihai site. Overall, this study provides valuable information to the aquaculture industry of southern China.