褶纹冠蚌钩介幼虫非寄生变态发育观察及早期稚蚌的生长

为揭示褶纹冠蚌钩介幼虫变态发育特征及过程,采用体外培养方法实现了褶纹冠蚌钩介幼虫的非寄生变态发育。运用光学显微镜和扫描电子显微镜对变态发育过程中幼虫外部形态、内部器官发育进行了系列观察,对非寄生变态发育的稚蚌后期生长发育进行跟踪研究,并分析了底泥和光照两种环境因子对稚蚌存活及生长的影响。结果显示:在整个培养过程中,钩介幼虫的外部形态及大小未出现显著性变化,而斧足、鳃丝、外套膜及内脏团等组织器官逐步形成;在培养第3天,幼虫可见斧足雏形,鳃丝、外套膜纤毛尚未发现;在培养第6天,斧足成形,可见斧足侧沟,外套膜纤毛稀疏,鳃丝出现;培养第9天,斧足纤毛、外套膜纤毛增多,鳃丝密集。稚蚌投喂30d后,鳃丝基本成形。养殖试验结果表明:底泥对稚蚌存活和生长具有显著影响（P < 0.01）,而光照无显著性影响（P>0.05）。该结果为蚌科钩介幼虫变态发育生物学研究积累了基础资料,也通过对稚蚌生长的评估证实了体外培养是蚌类人工繁育及保护的有效技术途径。     

背角无齿蚌生殖细胞及钩介幼虫的扫描电镜观察

本文报告背角无齿蚌的精子、卵子、钩介幼虫的扫描电镜观察。精子头部呈椭圆形，由顶体帽、顶体后区、核区和颈部组成，尾细长呈线状，卵子圆形，有许多卵闰，在生殖腺中有各种不同发育程度的卵细胞，钩介幼虫在育儿囊（外鳃）中发育，有一系列变态过程，表明卵子是分期分批排出，钩介幼虫也是分批发育和成熟的。     

紫黑翼蚌钩介幼虫寄主鱼的人工筛选及寄生包囊形成观察

选取16种鱼类, 对紫黑翼蚌(Potamilus alatus)钩介幼虫寄主鱼进行人工筛选试验, 结果表明: 仅在淡水石首鱼(Aplodinotus grunniens)上获得变态发育的稚蚌, 寄生变态率为(49.6±9.4)%, 但是过量寄生将导致淡水石首鱼的死亡。除眼斑拟石首鱼(Soiaenops ocellatus)外, 寄生在其他14种淡水鱼类均不可能实现钩介幼虫的变态。进一步扫描电镜观察显示: 钩介幼虫可在与淡水石首鱼同科的眼斑拟石首鱼鳃丝寄生并形成完整的包囊, 且在大规格鱼体形成包囊的速度明显快于幼鱼。但在寄生和淡水低渗双重胁迫下, 眼斑拟石首鱼出现极高的死亡率, 提示应进一步开展淡化驯养以提高眼斑拟石首鱼寄生后的成活率。其中黄颡鱼(Pelteobagrus fulvidraco)、小口黑鲈(Micropterus dolomieu) 、蓝鲶(Ictalurus furcatus)寄生后1—2d内脱落的幼虫几乎全部死亡, 推测3种鱼体中可能存在紫黑翼蚌幼虫的致死因子。综合研究表明: 紫黑翼蚌是目前发现对寄主鱼选择性最为专一的蚌类, 而眼斑拟石首鱼具有作为替代寄主鱼的潜能。     

绢丝丽蚌胚胎发育的研究

绢丝丽蚌卵为均黄卵,爱精卵在雌蚌外鳃中进行胚胎发育,其卵裂为不等完全卵裂。在秋季自然常湿（水温变幅为２４－８℃）时,胚胎发育历时５１ｄ,经过卵裂期、原肠期,发育为具有透明原壳、过钩、闭壳肌丝、内足丝、刚毛和外足丝的成熟钩介幼虫。胚胎发育的不同时期与外鳃特征具相关性。     

背瘤丽蚌胚胎发育的初步研究

用显微技术研究了背瘤丽蚌(Lamprotula leai)胚胎发育和钩介幼虫结构。结果表明,背瘤丽蚌卵为均黄卵,受精卵分布在雌蚌内、外鳃腔中进行胚胎发育;胚胎发育同步;胚胎发育过程包括受精卵、卵裂期、囊胚期、原肠期、膜内钩介幼虫期和钩介幼虫期;卵裂为螺旋不等完全卵裂;未受精的成熟卵在鳃腔内退化;胚胎发育期与胚胎、外鳃和内鳃颜色相关;怀卵母蚌胚胎在外界环境变化时容易全部流产。分析认为背瘤丽蚌胚胎发育期的繁殖特征可指导人工苗种生产。     

蚌科钩介幼虫比较形态学研究 I.四个种幼虫的形态

本文报道圆顶珠蚌,鱼尾楔蚌,中国尖嵴蚌,卵形脊嵴蚌育儿囊的特点和钩介幼虫的形态,应用光镜和扫描电镜对四种蚌的钩介幼虫形态进行了观察和比较,结果表明,四种蚌的育儿囊均为外鳃类的同生型,钩介幼虫为有钩型幼虫的大小,形状,壳表面,壳钩,棘刺,幼虫丝,感觉毛等在不同种之间存在着差异,文中对这些特征在分类上的意义进行了讨论。     

蚌科钩介幼虫的比较形态学研究Ⅱ.六个种幼虫的形态

研究了真柱矛蚌、剑状矛蚌,洞穴丽蚌、角月丽蚌、三解帆蚌、褶纹完蚌等六种蚌的育作囊的类型和钩介幼虫的形态,应用光镜及扫描电僮对钩介幼虫的形态结构进行了观察和比较。结果表明 柱矛蚌、剑状矛蚌、三角帆蚌、褶纹冠的育儿囊为外鳃类同生型,洞穴丽蚌、角月丽蚌的育儿囊为外鳃类四生型、钩介幼虫可为二类：真柱矛蚌、剑状矛蚌、褶 纹冠蚌为有钩型,三角帆蚌、油穴丽蚌、角月丽蚌为无钩型。一些细微结构在不同种之间也存在着差     

蚌科钩介幼虫比较形态学研究──Ⅰ.四个种幼虫的形态

本文报道圆顶珠蚌、鱼尾楔蚌、中国尖嵴蚌、卵形尖嵴蚌育儿囊的特点和钩介幼虫的形态。应用光镜和扫描电镜对四种蚌的钩介幼虫形态进行了观察和比较。结果表明,四种蚌的育儿囊均为外鳃类的同生型,钩介幼虫为有钩型,幼虫的大小、形状、壳表面、壳钩、棘刺、幼虫丝、感觉毛等在不同种之间存在着差异。文中对这些特征在分类上的意义进行了讨论。     

三角帆蚌钩介幼虫在两种寄主鱼上的寄生效果及其对寄主鱼血浆生化指标的影响

利用黄颡鱼(Pelteobagrus fulvldraco)、尼罗罗非鱼(Tilapia nilotica)对三角帆蚌(Hyriopsis cumingii)钩介幼虫进行了寄生实验,分析了幼虫在寄主鱼上的寄生周期和脱落数量与寄主种类、寄主鱼单尾体重的相关关系.以未寄生幼虫的罗非鱼为空白对照,测定分析了罗非鱼在幼虫寄生前、脱落后主要血浆生化指标的变化.实验结果显示:黄颡鱼、罗非鱼平均每千克体重脱落稚贝的数量分别为(26 435±6 430)只、(26 327±3 091)只,两种寄主鱼间不存在显著差异;脱落的稚贝数量随着寄主鱼体重的增加而增加,并呈显著线性相关.在水温(24±1)℃条件下,黄颡鱼组、罗非鱼组的稚贝脱落高峰分别出现在寄生后的第8 d、第7 d,罗非鱼组表现为明显的"早脱落"现象.罗非鱼在寄生前后血浆总蛋白(TP)、白蛋白(Alb)、总糖(Glu)、总胆固醇(Tc)和高密度脂蛋白(HDL)含量均未出现显著变化,而血浆甘油三酯(TG)、低密度脂蛋白(LDL)含量显著下降(P=0.001,0.020).未寄生组罗非鱼的7项指标均未出现明显变化.实验结果将为三角帆蚌钩介幼虫变态发育相关营养因子的探讨提供理论参考.     

不同生境蚶形无齿蚌的形态观察

对不同生境下蚶形无齿蚌壳的形态、育儿囊的类型和结构以及钩介幼虫等进行了比较研究。结果表明,在不同生境下,蚶形无齿蚌个体大小有很大差异,壳具有高度的可塑性;育儿囊由两片外鳃构成,为外鳃类的同生型,钩介幼虫在育儿囊内呈散乱状态存在;在小同区域,钩介幼虫的大小不同,但其壳高与壳长的比例却是一致的,且不同生境钩介幼虫的超微结构相同,均为有钩型。     

Persistence of host response against glochidia larvae in Micropterus salmoides

Host fish acquire resistance to the parasitic larvae (glochidia) of freshwater mussels (Unionidae). Glochidia metamorphose into juvenile mussels while encysted on host fish. We investigated the duration of acquired resistance of largemouth bass, Micropterus salmoides (Lacepède, 1802) to glochidia of the broken rays mussel, Lampsilis reeveiana (Call, 1887). Fish received three successive priming infections with glochidia to induce an immune response. Primed fish were held at 22-23 degrees C and were challenged (re-infected) at intervals after priming. Metamorphosis success was quantified as the percent of attached glochidia that metamorphosed to the juvenile stage and were recovered alive. Metamorphosis success at 3, 7, and 12 months after priming was significantly lower on primed fish (26%, 40%, and 68% respectively) than on control fish (85%, 93%, and 92% respectively). A second group of largemouth bass was similarly primed and blood was extracted. Immunoblotting was used to detect host serum antibodies to L. reeveiana glochidia proteins. Serum antibodies were evident in primed fish, but not in naive control fish. Acquired resistance of host fish potentially affects natural reproduction and artificial propagation of unionids, many of which are of conservation concern.     

Does the parasitic freshwater pearl mussel M. margaritifera harm its host?

Many parasites have strong negative impacts on their hosts, but the effects of single-host, non-trophically transmitted parasites can be subtle and are not well understood. We examined the physiological response of juvenile brown trout (Salmo trutta) to encystment by the parasitic larvae (glochidia) of the freshwater pearl mussel, Margaritifera margaritifera. Glochidia abundance was positively correlated to host body size and was accompanied by significant spleen enlargement at 31 days postexposure, but not before (15 days) or after (160 days). Compared to controls, encysted gill lamellae were significantly thicker and longer, and tended to have fewer mucous cells which may have facilitated encystment. There were no significant difference in mean blood haematocrit between encysted and uninfected trout, but encysted trout took c. 6 h longer to reach basal ventilation rate than controls suggesting that glochidiosis may impose a respiratory burden to brown trout. These findings may have implications for the artificial propagation of the freshwater pearl mussel because the effects of glochidia on host respiratory performance appear to be additive. Therefore, aiming for high glochidia loads may not be the best option for mussel propagation programmes, if this compromises host fitness and hence the probability of successful glochidia excystment.     

Acquired resistance of bluegill sunfish Lepomis macrochirus to glochidia larvae of the freshwater mussel Utterbackia imbecillis (Bivalvia: Unionidae) after multiple infections

The effects of multiple infections on the host-parasite relationship between bluegill sunfish (Lepomis macrochirus) and parasitic glochidial larvae of the freshwater mussel Utterbackia imbecillis were examined. Na?ve, young-of-the-year bluegills were infected with glochidia and placed in individual observation chambers. Each day, water was drained from each chamber and the numbers of dead glochidia, live glochidia, partially metamorphosed glochidia, and fully metamorphosed juvenile mussels were counted. The same fishes were infected a total of 4 times. After 2 infections, the fish began to exhibit evidence of acquired resistance to glochidia. During the third and fourth infections, this resistance was clearly evidenced by the marked increase in the percentage of dead and live glochidia shed during the first 5 days of the infection and by the significant decrease in the success of metamorphosis. The total number of glochidia that successfully attached to the fish decreased significantly during the fourth infection relative to the first. The number of larvae attached to the host fish was positively correlated with the size of the fish during the first infection but was negatively correlated during all subsequent infections. Variance to mean ratios indicated that larvae were aggregated among host fishes during the infections. This study has important implications in propagation and conservation efforts of this endangered group of organisms.     

Influence of cortisol on the attachment and metamorphosis of larval Utterbackia imbecillis on bluegill sunfish (Lepomis macrochirus)

The larvae of unionid freshwater mussels (i.e., glochidia) undergo a parasitic stage requiring their attachment to the external epithelia of fish hosts, where they metamorphose into free-living juveniles. We describe the physiological effects in bluegill sunfish (Lepomis macrochirus) of infection with glochidia from the paper pondshell (Utterbackia imbecillis). Glochidia accumulation on bluegill increased dramatically at concentrations of 2000 glochidia liter(-1) and above, reaching a maximum attachment density of about 30 glochidia g(-1) fish at 4000 glochidia liter(-1). Plasma cortisol was the most sensitive indicator of biological effect to glochidial exposure, increasing significantly in hosts exposed to 2000 glochidia liter(-1) or greater. Glochidia were 31% more likely to undergo successful juvenile metamorphosis when attached to bluegill with elevated plasma cortisol, largely due to the enhanced survivorship of these larvae during the first 48 h after infection. We tested the hypothesis that glochidial attachment and juvenile metamorphosis were stimulated directly by plasma cortisol in fish hosts. Bluegill were given an intraperitoneal injection of cortisol, then infected with 1000 glochidia liter(-1) at 48 h after hormone supplementation. Cortisol-injected fish had a 42% increase in the number of attached glochidia g(-1) fish and a 28% increase in larval metamorphosis compared to sham-injected and control fish. We provide evidence that cortisol enhances glochidial metamorphosis on hosts by improving the retention of attached glochidia. This study gives insights into the influence of host physiology on glochidial attachment and juvenile mussel transformation.     

Parasite‐induced alterations of host behaviour in a riverine fish: the effects of glochidia on host dispersal

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Do individual Activity Patterns of Brown Trout (Salmo trutta) alter the Exposure to Parasitic Freshwater Pearl Mussel (Margaritifera margaritifera) Larvae?

The hypothesis that interindividual differences in the activity of brown trout alter the exposure to parasitic freshwater pearl mussel glochidia was tested in a Swedish stream. Wild yearling brown trout (N = 103) were caught, individually tagged for identification and scored for open‐field activity during standardized laboratory tests in June. Fifty gravid freshwater pearl mussels were relocated to the stream, where after the trout were released back into the stream. The fish were recaptured in October (N = 35), checked for glochidia encystment (infested individuals: n = 6) and re‐scored for open‐field activity traits. Swimming velocity during the test was higher in fish infected with glochidia, suggesting that high activity could increase their exposure to glochidia. Potentially, as metabolism rate and ventilation rate typically increase with activity, elevated activity may lead to an increased likelihood of glochidia passing over the gills. This novel finding suggests that glochidia infestation is non‐random and that the behaviour of the host fish can influence the likelihood of glochidia infestation.     

Practical experience in the rearing of freshwater pearl mussels (Margaritifera margaritifera): advantages of a work-saving infection approach,survival, and growth of early life stages

The critically endangered freshwater pearl mussel (Margaritifera margaritifera Linnaeus 1758) is the target species of an Austrian conservation project that involves captive breeding. In order to optimize the operational procedure, controls were conducted at several decisive stages, including infection of host fish (for which a time- and work-saving enclosure approach was tested), larval growth during the parasitic stage, growth of juvenile mussels in climate chambers at different temperatures, and growth and survival of re-introduced juveniles in field cages. High infection rates could be attained under near natural conditions. Distinctive patterns in the way the gill arches of the host fish were infected could be detected. Encysted glochidia showed significantly different successive growth stages, related to water temperature. In all, five distinctive growth stages could be detected in the course of the first 562 days of observation. The stages are described and the respective daily increments given. Very high survival rates were achieved during hibernation in the field as well as at the laboratory. The study suggests a way for saving time in the infection procedure that can more effectively be invested in an intensive maintenance of juveniles at the laboratory and during hibernation in the field.     

A delayed effect of the aquatic parasite <Emphasis Type="Italic">Margaritifera laevis</Emphasis> on the growth of the salmonid host fish <Emphasis Type="Italic">Oncorhynchus masou masou</Emphasis>

Parasitic species often have detrimental effects on host growth and survival. The larvae of the genus Margaritifera (Bivalvia), called glochidia, are specialist parasites of salmonid fishes. Previous studies have reported negligible influences of the parasite on their salmonid hosts at natural infection levels. However, those studies focused mainly on their instantaneous effects (i.e., during the parasitic period). Given the time lag between physiological and somatic responses to pathogen infections, the effect of glochidial infection may become clearer during the post-parasitic period. Here, we examined whether the effect of glochidial infections of Margaritifera laevis on its salmonid host Oncorhynchus masou masou would emerge during the post-parasitic period. We performed a controlled aquarium experiment and monitored fish growth at two time intervals (i.e., parasitic and post-parasitic periods) to test this hypothesis. Consistent with previous observations, the effects of glochidial infection were unclear in the middle of the experiment (day 50; parasitic period). However, even with a natural glochidial load (48 glochidia per fish), we found a significant reduction in growth rates of infected fish in the extended period of the experiment (day 70; post-parasitic period). Our results suggest that examining only instantaneous effects may provide misleading conclusions about mussel–host relationships.