Experimental challenges of juvenile and adult Manila clams with the protozoan Perkinsus olseni at different temperatures

Infection with Perkinsus species, primarily P. olseni, is thought to be a major cause of the decline of Manila clam populations in Japan since the 1980s. However, the pathogenicity of the infection has not been sufficiently evaluated to estimate the impact of infection on wild Manila clam populations. We experimentally challenged juvenile (3- to 6-mm shell length) and adult (18- to 22-mm shell length) Manila clams with P. olseni at 18, 23, 28, and 30 °C. Mortality was significantly higher in challenged groups than in control groups. The difference in mean mortality between the challenged and control groups (all life stages and temperatures) was only significant above a threshold of infection intensity ~10⁶ cells/g soft wet tissue (SWT). As temperature increased, the onset of mortality occurred more rapidly. The increase in mortality occurred earlier in juveniles than adults at 28 °C and lower. Our results suggest that the pathogenicity of P. olseni is higher in juveniles than in adults and at higher water temperatures. Given the infection intensities (ca. 10⁶ cells/g SWT) previously reported in wild Manila clams, the parasite likely has considerable impact on wild Manila clam populations, particularly juveniles during periods of high temperature.     

Protein expression profiling in haemocytes and plasma of the Manila clam Ruditapes philippinarum in response to infection with Perkinsus olseni

The protein expression profiling in clam haemocytes and plasma in response to Perkinsus olseni was addressed. Adult Manila clams from a P. olseni‐free bed were experimentally challenged with parasite zoospores to analyse immune response. In another experiment, the effects of longer term infection were assessed in adult clams collected from a P. olseni‐affected bed, by comparing moderate to very heavily infected clams with non‐infected ones. Haemocyte and plasma proteins were separated by two‐dimensional electrophoresis; spot patterns were qualitatively compared between treatments within each experiment and the spots indicating differential protein expression associated with P. olseni challenge or with field infection were processed for protein identification. Fifteen clam proteins (four in haemocytes and eleven in plasma) of which expression was markedly affected by P. olseni were identified. Some of the identified proteins have a well‐known role in clam immune response against the parasite, such as lysozyme and lectins. Rho GTPase‐activating protein 6 could be a marker of resistance against P. olseni, which should be further studied.     

贝类对对虾养殖池塘沉积物中小型底栖动物的影响

通过分析凡纳滨对虾单养及其与泥蚶混养实验的沉积物的理化特性、小型底栖动物种类组成及其生物量的变化,研究贝类对对虾池中小型底栖动物的影响。实验中对虾放养密度均为17×10~4个/hm~2,泥蚶密度分别为0粒/m~2(S)、60粒/m~2(SC1)、120粒个/m~2(SC2)和180粒/m~2(SC3)。结果显示,随养殖时间增加:(1)沉积物中有机物含量呈上升趋势,pH与氧化还原电位逐渐下降;随贝类放养密度增加,底质环境恶化程度趋缓;(2)小型底栖动物的丰度和生物量呈下降趋势,随着贝类放养密度增加,小型底栖动物的群落结构变化逐渐减少;(3)回归分析表明,介形类与线虫比值与对虾产量呈较好的相关性,一定密度贝类混养有利于底泥中介形类与线虫比值的提高,初步结果为养殖过程中该比值平均要达到6,单次值不低于3.5。研究表明,对虾与泥蚶混养有利于底质的改善和小型底栖动物的生长,较高密度的泥蚶(80~140个/m~2)有明显净化底质的作用。     

Application of enzyme-linked immunosorbent assay (ELISA) for the study of reproduction in the Manila clam Ruditapes philippinarum (Mollusca: Bivalvia): II. Impacts of Perkinsus olseni on clam reproduction

We investigated the effects of infection by the protozoan Perkinsus olseni on the reproduction of female Manila clams, Ruditapes philippinarum, from a population in Gomso Bay, Korea. The reproductive effort of the clams was assessed by ELISA using a clam egg-specific antibody and was expressed as a weight-based gonadosomatic index (GSI). The number of Perkinsus infecting each clam was estimated from the gills using Ray's fluid thioglycollate medium (RFTM) along with a NaOH digestion assay. We found that reproductive effort was negatively correlated with the intensity of the Perkinsus infection: more heavily infected clams produced fewer eggs during the spawning period from May to August. Frequency of spawning was also negatively correlated with the level of Perkinsus infection; heavily infected clams (HIC) exhibited a single spawning pulse in late July, whereas lightly infected clams (LIC) showed three spawning peaks in mid-May, late July, and late August. Egg production of HIC was only 30–75% of LIC during spawning. The level of total protein in LIC was also higher year round than in HIC. In conclusion, our investigation demonstrates that a high level of Perkinsus infection affects spawning frequency and reduces egg production, which may have long-term impacts on clam recruitment and population growth.     

小窑湾高密度贝类筏式养殖对浮游植物群落的影响

20 0 0年 3～ 1 1月小窑湾水域浮游植物海上调查结果表明 ,在高密度贝类筏式养殖区随着贝类摄食强度的增强 ,浮游植物数量、种类都大量减少 ,其年平均细胞数量偏低 ,仅为 56× 1 0 4/m3 ,种类44种 ;高密度贝类筏式养殖区的浮游植物群落多样性指数偏低 ,丰度指数偏低 ,均匀度指数因季节不同而有较大差异     

双壳贝类能量学及其研究进展

对贝类能量收支方程C＝P＋R＋U＋F中各组分的意义和测定方法及其研究的状况进行了较为全面的阐述。     

三种淡水贝类对藻类消除作用的初步研究

本试验比较了褶纹冠蚌、三角帆蚌与河蚬等三种淡水贝类24h内对水族箱中藻类的消除量、消除率及0-4h三种贝类对藻类的消除效率（Ki）。结果表明：（1）褶纹冠蚌、三角帆蚌与河蚬第24h对藻类的消除率分别达到74.3±2.9%,75.6±2.1%,88.4±3.1%,三种淡水贝类对藻类的消除效果显著;（2）t检验表明,24h内河蚬对藻类的消除率、消除量显著大于褶纹冠蚌、三角帆蚌（P<0.05）。河蚬试验组0-4h Ki值显著大于褶纹冠蚌、三角帆蚌（P<0.05）;（3）三角帆蚌对藻类的消除量随着贝类密度的增加显著增加。河蚬、褶纹冠蚌对藻类的消除效果受密度制约,12h后河蚬20g/L试验组与其它河蚬试验组相比对藻类的消除量最大。褶纹冠蚌消除藻类的最佳密度为40g/L。     

几种药物治疗鲤鱼暴发细菌性出血病的效果

池塘高密度集约化养殖鲤鱼极易发生细菌性出血病。 2 0 0 0年 6～ 8月 ,宁夏大部分养殖场暴发此病 ,发病面积一万多亩 ,平均死亡率 2 5 %左右 ,危害严重且不易治疗 ,复发率高。为此 ,宁夏水产技术推广站、宁夏鱼病研究防治中心组织技术人员深入基层进行了不同药物防治效果的研究 ,旨在探索出一套好的方法和筛选出一种防治暴发性出血病最有效的药物 ,降低防治成本 ,减轻渔农负担。1　病原鲤鱼暴发细菌性出血病是由嗜水气单胞菌嗜水亚种感染鱼体组织引起的鱼病。病原菌属弧菌科、气单胞菌属 ,细胞直杆状、两端圆、直径 1 0～ 4 4μｍ ,以极生…     

Possible cytotoxic effects of the dinoflagellate, Gyrodinium aureolum, on juvenile bivalve molluscs

Juveniles of eight commercially important species of bivalve molluscs (Spisula solidissima, Argopecten irradians, Crassostrea virginica, Mytilus edulis, Mya arenaria, Ostrea edulis, Mercenaria mercenaria, Placopecten magellanicus) were exposed in the laboratory to the commonly occurring dinoflagellate, Gyrodinium aureolum. Histological analyses of gut tissues indicated that the impact of G. aureolum on the shellfish was species-specific. High rates of mortality were noted in the bay scallop, A. irradians, but not in other molluscan species. There were no pathological differences between control animals and animals fed G. aureolum in S. solidissima, M. arenaria, or M. mercenaria. The most severely affected molluscs were C. virginica and A. irradians. C. virginica did not exhibit differences in digestive gland parameters between control and experimental animals; however, several animals did show significant mantle and gill lesions. Bay scallops exhibited decreased height of absorptive cells and increased lumen diameter after exposure to Gyrodinium suggesting, at least, poor food quality of Gyrodinium. Evidence of toxic effects was not identified in the digestive gland. Several bay scallops also showed variable amounts of inflammation in the kidney associated with protozoal infestations and variable amounts of predominately rod-shaped bacteria within the urinary space. Aquaculturists, especially of scallop species, should monitor for the presence of G. aureolum. Given its large size (25-30 m), G. aureolum could be filtered from incoming water to hatcheries, thus avoiding mass mortalities of spat and juvenile scallops.     

四种常用渔药对胃瘤线虫幼虫的杀灭试验

针对慈溪市饮用水水库底层鱼类相继发生胃瘤线虫危害鱼体生长发育、影响鱼产品质量的情况 ,笔者在调查、取样的基础上 ,选用了鱼苗鱼病防治中四种常用药物 :90 %晶体敌百虫、甲苯咪唑、盐酸左旋咪唑、肠虫清 (阿苯达唑 )等进行幼虫杀灭试验 ,试验方法采用等对数间距法 ,结果表明 :这四种药物对胃瘤线虫幼虫均有杀灭效果 ,其中甲苯咪唑毒性最强 ,90 %晶体敌百虫、盐酸左旋咪唑次之 ,肠虫清毒性最弱。     

有机污染提高双壳贝类对弧菌易感性的研究↑（*）

在实验室条件下,通过投饵不换水所形成的有机污染来研究有机污染提高双壳贝类对弧菌的易感性。结果表明,有机污染时间越高长,弧菌的浓度越高;弧菌的数量与有机污染环境中氨及无机氮（ＴＩＮ） 呈显著的正相关,与亚硝酸盐（ＮＯ－２ － Ｎ） 和总有机碳（ＴＯＣ） 有比较明显的正相关;试验贝类死亡与弧菌浓度呈正相关,它们对弧菌的易感性依次为栉孔扇贝、虾夷扇贝、太平洋牡蛎、海湾扇贝、紫贻贝。     

Improving bivalve fishery management: The development of a tool to forecast bivalve reproductive season based on environmental data from satellite remote sensing observations

Donax trunculus is a much‐appreciated commercial clam whose natural populations have been overexploited in southern–western Spain during the last decades. In order to control the decrease of natural beds, local governments establish annual closed seasons based on socioeconomic reasons, such as economic necessity or tourism interest. The objective of this study was to develop an efficient tool for predicting gonadal stages based on environmental condition data. This tool will allow for an improvement in fishery management since in this manner the closed season can be based on the reproductive cycle. The natural population's reproductive cycle was studied for more than 2 years. The obtained gonadal and condition indexes (GI and CI) values were statistically related to environmental conditions, specifically surface seawater temperature (SST) and chlorophyll‐a (Chlo‐a) levels with these data being provided from satellite remote sensing observations (SRS). The best statistical relationship was obtained between GI and the SST registered 60 days before bivalve sampling (SST‐60). The regression equation allows for an estimate of GI value based on the SST‐60 and, as each value is related with one gonadal stage (resting, maturation, ripe), for prediction of the reproductive cycle. Therefore, the closed season can be established when most of the population is in the ripe stage and can be adjusted taking into account the possible temperature variations across the years. For ease of use, GI values estimated with this tool have also been converted using different colours onto a map of wedge clam reproductive stages in its natural beds.     

钝缀锦蛤繁殖周期和胚胎发育

2013年8月至2014年7月,采用组织学和实验生态学方法对钝缀锦蛤(Tapes conspersus)的性腺发育、生殖周期、肥满度、胚胎和幼虫发育进行了研究。结果显示,钝缀锦蛤性腺发育以1年为1个周期,性腺发育过程可分为增殖期、生长期、成熟期、排放期和休止期5个时期;繁殖期在每年10月至翌年3月,繁殖盛期为3月、10月和11月(水温20.3~24.6℃),分批产卵。8月肥满度最高,为33.43%;4月最低,为18.31%。钝缀锦蛤卵径为70~80μm;在水温24~26℃、盐度28~32条件下,受精卵经16 h左右发育为D形幼虫;初孵D形幼虫大小为90~110μm,浮游幼虫经7~8 d培育进入附着变态期,此时壳长为210~230μm,再经4~5 d发育变态为稚贝。本研究为钝缀锦蛤的人工繁育及种质资源保护和利用提供了基础资料。     

Characterization of vitamin B12 compounds from the brackish-water bivalve Corbicula japonica

In Lake Togo (Tottori prefecture, Japan), the vitamin B₁₂ content of the brackish-water bivalve Corbicula japonica remained high (17.3–22.5 μg/100 g wet weight of the edible portion) throughout the year, except during August and September. We evaluated whether the bivalve contained true vitamin B₁₂ or other corrinoid compounds that are inactive in humans by purifying the compounds and identifying them using LC/ESI–MS/MS chromatograms. The results indicated that “true” vitamin B₁₂ predominated in the bivalve, although small amounts of inactive corrinoid compounds (pseudovitamin B₁₂ and three unidentified compounds) were also found.     

The effect of salinity change on the burrowing behavior of an adult brackish water bivalve Corbicula japonica

Fisheries Science - The brackish water bivalve Corbicula japonica, a target species for seedling release in Japan, inhabits environments subject to drastic salinity changes. The burrowing behavior...     

Purification of a proteinase produced by the bivalve pathogen Vibrio alginolyticus NCMB 1339

Abstract. A proteinase produced by the bivalve pathogen Vibrio alginolyticus NCMB 1339 was purified by preparative isoelectric focusing and gel filtration. Proteinase activity was associated with two components of molecular weights 43000 and 41000 and was toxic to larval Ostrea edulis . Production of this enzyme was maximal during the late exponential phase of growth and it remained stable throughout the stationary phase of growth. At 37°C, activity against azocasein was optimal at pH 7–5. The enzyme was inhibited by mercuric chloride, dithiothreitol and ethylene diamine tetra-acetic acid, but not by pepstatin-A, phenylmethylsulphonyl-fluoride or tosyl-L-lysine chloromethylketone.     

The effect of ration size on the growth and growth efficiency of the bivalve mollusc Tapes japonica

The growth and gross growth efficiency of small Japanese little-neck clams, Tapes japonica, were investigated under two sets of experimental conditions. Over a 21-day period, growth of the clams, measured as an increase in dry weight and meat protein-N, was found to be correlated with the quantity of algal protein-N available and the amount of algal protein-N actually consumed by animals maintained at three different phytoplankton levels. With an increase in the quantity of phytoplankton presented there was a proportional increase in the quantity consumed and an increase in growth. The gross growth efficiency, based on the protein-N content of the algae consumed and the dry meat gain in protein-N, was highest at the lowest phytoplankton level (48%). At the two other phytoplankton levels there was little difference in growth efficiency, and it averaged 37.6%. Two tank designs were used in the study, one in which the fecal matter settled out of suspension and one in which the fecal material was continuously resuspended. There was little difference in the growth achieved using either tank design.     

A generalized growth and mortality model for assessing the economics of bivalve culture

A method is described for extrapolating the results from bivalve growth trials to cover either longer time periods or different size ranges. Examples of general size-related trends in growth and mortality rates of oysters, Ostrea edulis L. and Crassostrea gigas Thunberg are given, and their application to an economic model is described. This can be used to make projections of the likely sizes, numbers surviving and hence value of a stock, from the time of relaying until marketable size is reached. The results can be subjected to discounted cash flow analysis as a technique of project appraisal and in optimizing ongrowing schedules. The initial part of the method can be used separately in monitoring batch-to-batch or year-to-year differences in growth performance.     

图丽鱼寄生破坏古氏虫的形态描述及系统发育

在调查新疆乌鲁木齐市观赏鱼感染寄生虫种类期间,从图丽鱼(Astronotus ocellatus)鳃部采集到一种单殖吸虫,经过形态学比较具有鉴定依据的背腹中央大钩、联接片、交接器等结构后,鉴定为锚首虫亚科(Ancyrocephalinae)的破坏古氏虫(Gussevia asota)。首次测定了破坏古氏虫28S rDNA基因序列(GenBank登录号:MG596661),系统发育分析表明,该虫与鲻鱼虫属(Ligophorus)、嗜丽鱼虫属(Cichlidogyrus)的亲缘关系较近,聚为稳定的独立分支。