First report and description of a Cyrilia sp. (Apicomplexa: Haemogregarinidae) from a freshwater Cururu Stingray Potamotrygon cf. histrix (Elasmobranchii: Potamotrygonidae), from the Amazon Region,Brazil

A haemogregarine is described in 12 cururu stingray (Potamotrygon cf. histrix), from Mariuá Archipelago, Negro River, in the Brazilian Amazon Basin. All animals, both male and female, were parasitized by the haemogregarine and parasitaemia varied between 0.8% and 10% of erythrocytes. The stages observed included trophozoites or merozoites, suspected meronts, and gamonts presumed to be of two types, macrogamonts and microgamonts. Most stages were observed inside mature erythrocytes, while others were extracellular. The stages observed were most similar to those characteristics of the genus Cyrilia, than to any other fish haemogregarine and may represent a new Cyrilia species.     

Notes on kidney-infecting species of the genus Sphaerospora Thélohan (Myxosporea), including a new species S. gobionis sp.nov., and on myxosporean life cycle stages in the blood of some freshwater fish

Abstract Freshwater fish in Czechoslovakia were examined for species of the genus Sphaerospora Thélohan, 1892 and for myxosporean life cycle stages in the blood. In addition to perch infected with S. pectinacea Bocharova & Donets, 1974, renal tubules of seven host species harboured thus far unidentified Sphaerospora species. A new species, S. gobionis sp.nov. is described from renal tubules of Gobio gobio. In populations of Gobio gobio, Tinea tinea and Rutilus rutilus harbouring infections with different Sphaerospora species, organisms identified as mobile myxosporean life cycle stages were detected in the blood, where they undergo a proliferative cycle. These organisms were reminiscent of stages in the blood of common carp fingerlings, supposedly identical with Sphaerospora renicola Dyková & Lorn. It is possible that the blood stages found in the three cyprinid hosts represent stages of the life cycle of their respective Sphaerospora species. If this is correct, further studies may show if the presence of proliferative stages in the bloodstream is a character distinctive of the genus Sphaerospora.     

Demonstrating the practical impact of studies on biotic interactions and adaptation of a threatened unionoid mussel (Margaritifera margaritifera) to its host fish (Salmo trutta)

1. To understand the ecological factors behind the decline of functionally important threatened species with complex life cycles, many different life‐cycle stages need to be investigated. The highly threatened unionoid freshwater mussels, with their complex life cycle, including a parasitic stage on host fish, often have a large influence on biodiversity and ecosystem functioning.
2. The overall aim of the present article is to summarize and discuss the impact of two articles published in Aquatic Conservation: Marine and Freshwater Ecosystems (AQC) on biotic interactions and adaptation of a threatened unionoid mussel (Margaritifera margaritifera) to its host fish (Salmo trutta).
3. The two AQC publications described research on the influence of population size and density of mussels and host fish, and host–parasite interactions between mussels and their host fish, on the recruitment of juvenile mussels.
4. The results from these publications filled gaps in knowledge and resulted in recommendations and incentives for conservation. The results and method development have been used in practical conservation work with threatened mussel species and have been implemented and cited in management handbooks. The outcome of the publications has been implemented in large conservation and restoration projects, and in several recent scientific publications.
5. Specifically, the results from one publication showed that ecological parameters such as mussel and host fish density and population size influenced recruitment of the threatened freshwater pearl mussel. The results from the second publication showed that understanding host–parasite interactions is important for comparing the suitability of host fish strains, and that host fish strains differ in their suitability for mussel infestations. In combination, the articles show that integrating ecological parameters of threatened mussels and their host fish with host–parasite interaction experiments can be an important influence on conservation recommendations, adaptive management and national management programmes for threatened species.

     

Betanodavirus: Dissection of the viral life cycle

Progressive research has been recently made in dissecting the molecular biology of Betanodavirus life cycle, the causative pathogen of viral encephalopathy and retinopathy in economic important marine fish species. Establishment of betanodavirus infectious clone allows the manipulation of virus genome for functional genomic study, which elucidates the biological event of the viral life cycle at molecular level. The betanodavirus strategizes its replication by expressing anti‐apoptosis/antinecrotic proteins to maintain the cell viability during early infection. Subsequently utilizes and controls the biological machinery of the infected cells for viral genome replication. Towards the late phase of infection, mass production of capsid protein for virion assembly induces the activation of host apoptosis pathway. It eventually leads to the cell lysis and death, which the lysis of cell contributes to the accomplishment of viral shedding that completes a viral life cycle. The recent efforts to dissect the entire betanodavirus life cycle are currently reviewed.     

Transmission Ecology and Larval Behaviour of Camallanus cotti (Nematoda, Camallanidae) Under Aquarium Conditions

The parasitic fish nematode Camallanus cotti has been reported from a number of freshwater fish species around the world. Its wide geographical distribution seems mainly to be the result of anthropogenic dissemination due to extensive ornamental fish trade. In most reports it is assumed that C. cotti's life cycle involves cyclopoid copepods as intermediate host and various freshwater fishes as final host. However, the species' relatively frequent and persistent occurrence in aquaria worldwide strongly indicates flexibility in its life cycle, i.e. the ability to infect the final host directly. The present study has shown that under aquaria conditions, without any presence of copepods, C. cotti is able to infect various phylogenetically distant fish species directly for at least three generations. It was further shown that the infective free-living first-stage larvae may survive for more than three weeks in the host-external environment and that their host-attracting behaviour is not precluding direct transmission to the final fish host. Any treatment for C. cotti under aquaculture or aquarium conditions should be directed towards both individual infected fish hosts as well as the free-living larvae on the substrate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tissue reactions to microsporidian infections in fish

Abstract. Histopathological studies on natural and experimental infections of nineteen microsporidian species from fishes distinguished two types of tissue reactions.
The first type is characteristic of infections with xenoma-inducing microsporidian species and comprises three successive stages: a weakly reactive stage, a productive stage with the formation of granulomas and a stage of granuloma involution. Following the first stage, tissue reactions are directed towards the isolation of the parasite and result in its complete elimination and host tissue repair. The extent of pathological changes probably depends on the number of parasite cells which initiated the infection.
The second type is represented by Pleistophora species infecting muscles or oocytes. Host tissue reaction is surprisingly slight during the schizogony and sporogony and does not tend to isolate the invaded muscle fibres. A slight lymphocytic infiltration of myosepta indicates the first stage of tissue reaction. The tissue reaction only reaches the productive stage when mature spores completely fill the contents of the infected muscle fibre. A thick wall of fibroblasts may be formed to demarcate the parasite mass as soon as it undergoes necrotic changes. The extent of pathological changes probably depends on the ability of early developmental stages of the parasite to spread the infection within the host.
In both types of tissue reaction, the spores are destroyed by complete digestion within host phagocytic cells.     

Piscirickettsiosis and Piscirickettsia salmonis in fish: a review

The bacterium Piscirickettsia salmonis is the aetiological agent of piscirickettsiosis a severe disease that has caused major economic losses in the aquaculture industry since its appearance in 1989. Recent reports of P. salmonis or P. salmonis‐like organisms in new fish hosts and geographical regions have increased interest in the bacterium. Because this gram‐negative bacterium is still poorly understood, many relevant aspects of its life cycle, virulence and pathogenesis must be investigated before prophylactic procedures can be properly designed. The development of effective control strategies for the disease has been limited due to a lack of knowledge about the biology, intracellular growth, transmission and virulence of the organism. Piscirickettsiosis has been difficult to control; the failure of antibiotic treatment is common, and currently used vaccines show variable long‐term efficacy. This review summarizes the biology and characteristics of the bacterium, including its virulence; the infective strategy of P. salmonis for survival and evasion of the host immune response; the host immune response to invasion by this pathogen; and newly described features of the pathology, pathogenesis, epidemiology and transmission. Current approaches to the prevention of and treatment for piscirickettsiosis are discussed.     

The life cycle of Chloromyxum auratum (Myxozoa) from goldfish, Carassius auratus (L.), involves an antonactinomyxon actinospore

The myxozoan parasite Chloromyxum auratum Hallett, Atkinson, Holt, Banner & Bartholomew, 2006 , was shown experimentally to have a two‐host life cycle which involved a previously undescribed antonactinomyxon actinospore stage. Myxospores obtained from gall bladders of naturally infected feral goldfish, Carassius auratus (L.), were used to infect samples of mixed species of oligochaete worms obtained from the same locality as the fish: Fern Ridge Dam, Oregon, USA. After some 110 days post‐exposure, actinospores were detected from the water above the oligochaetes. The 18S rDNA sequence of these actinospores was identical to the original myxospores. Spore release was sporadic, of low intensity and short duration, which confounded efforts to identify the host oligochaete species and infect naïve fish. This is the first life cycle that incorporates an actinospore of the collective group Antonactinomyxon, and the first life cycle demonstrated in the laboratory for a species of Chloromyxum.     

The life cycle of Henneguya nuesslini Schuberg & Schroder, 1905 (Myxozoa) involves a triactinomyxon-type actinospore

The life cycle of the histozoic myxozoan parasite Henneguya nuesslini was investigated in two salmonid host species. Naive brown trout, Salmo trutta, and brook trout, Salvelinus fontinalis, were experimentally infected in two trials by triactinomyxon type actinospores from naturally infected Tubifex tubifex. In exposed common carp, Cyprinus carpio, no myxospore production was detected. The parasite formed cysts with mature myxospores in the connective tissue of the fish 102 days post-exposure. The morphology of both actinosporean and myxosporean stages was described by light microscopy and a 1417-bp fragment of the 18S rDNA gene was sequenced. Sequence analysis confirmed the absolute congruence of the two developmental stages and assisted in determining species identity. Host range, tissue specificity and myxospore measurements provided sufficiently distinctive features to confirm species validity and were thus crucial for identification. The triactinomyxon spores had 16 secondary germ cells, unique dimensions, a very opaque sporoplasm matrix and three conspicuously protruding, pyriform polar capsules. This is the first record of a Henneguya sp. life cycle with a triactinomyxon-type actinospore, which suggests a close relationship with the Myxobolus group and a polyphyletic origin of the genus Henneguya.     

Comparative experimental infection of the copepod Paracartia grani with Marteilia refringens and Marteilia maurini

Paracartia grani (Copepoda) has been identified as a potential intermediate host in the life cycle of Marteilia   refringens , a paramyxean parasite infecting flat oysters. However, no intermediate host has yet been identified for Marteilia maurini that infects mussels. A better understanding of the life cycle of these two Marteilia types would clarify their taxonomic relationship and hypothesized co-specificity. For this purpose, experimental infections of copepods, P. grani , were performed using naturally infected flat oysters and mussels. Infection patterns were different depending whether copepods were infected from oysters or mussels. M. maurini did not proliferate in copepods while M. refringens rapidly proliferated in infected copepods. Previously unrecognized developmental stages of M. refringens were found during this study.     

Ultrastructural observations of the life cycle stages of Ameson atlanticum sp. nov., a microsporidan parasitizing Cancer pagurus L.

Abstract. Cancer pagurus (Cancridae) from the Atlantic coast of France is parasitized by a new species of microsporida Ameson atlanticum sp. nov. The main stages of the life cycle of the parasite are a monokaryotic and then diplokaryotic meront, tetranucleate (at least) sporont fsporogonial sporont), uninucleate sporoblast and spore. The spore (1.9 × 1.5 μm) possesses 11–12 coils of the polar filament and a lamellar polaroplast. Hairlike appendages are present on the surface of the sporoblastic plasmodium, sporoblast and spore. All stages take place in direct contact with the muscular tissue of the crab. Infection provokes the destruction of 80% of host muscle myofibrils.     

褐藻羊栖菜繁殖生物学特征和生活史流程的补充研究

以温州市洞头区人工养殖羊栖菜和野生羊栖菜为研究样本,详细描述了羊栖菜成熟孢子体有性生殖,假根与侧生枝无性生殖的繁殖生物学特征和生活史流程。详细记录了羊栖菜卵、精子和受精卵的减数分裂和有丝分裂过程,假根、茎(主茎和侧生茎)、叶(气囊)和生殖托(雌托和雄托)等4类器官生长、发育和分化过程,胚、幼孢子体和成熟孢子体形态结构特征。在此基础上对现有羊栖菜繁殖生物学特征及生活史流程进行了补充和修正,增加了羊栖菜侧生枝无性生殖和羊栖菜幼孢子体期有性生殖的相关内容,并重新绘制了羊栖菜生活史流程图。该研究结果将为开展羊栖菜养殖生态学研究,深层次解析羊栖菜生殖节律、种群繁衍与环境关系奠定基础。     

Occurrence of postmortem myoliquefactive kudoosis in Atlantic mackerel, Scomber scombrus L., from the North Sea

Members of the myxosporean genus Kudoa occur in various marine teleosts worldwide. Several species are of concern to the fishery and aquaculture industries as they may produce unsightly cysts in the fish host's musculature or are associated with postmortem myoliquefaction of the fish muscle, commonly referred to as 'soft flesh'. This study describes the occurrence and effects on a host of a Kudoa species in Atlantic mackerel, Scomber scombrus , from the northern North Sea. Generalized postmortem myoliquefaction associated with Kudoa sp. occurred in 0.8% of the examined fish, i.e. 11 of 1339 mackerel developed 'soft flesh'. There was a significant difference in the prevalence of myoliquefaction between medium sized (400–600 g) and large mackerel (>600 g). The prevalence reached 8.9% in the latter host size group. No subclinical infections of Kudoa sp. were detected when examining fresh muscle ( n  = 103) and blood ( n  = 165) samples for spores using light microscopy. Affected mackerel developed generalized myoliquefaction after 38–56 h post-catch. No inflammatory host response was associated with the presence of plasmodia within single body muscle fibres of 'soft flesh' affected fish. Based on comparison of myxospore dimensions and analysis of the nuclear small subunit (SSU) ribosomal DNA, the present Kudoa species is assigned to Kudoa thyrsites . However, due to the species' apparently very wide geographical distribution and host range, its varying effect on different fish host species, together with the still unknown life cycle of Kudoa spp., the taxonomic status of K. thyrsites appears not to be fully resolved.     

海水鱼蛭阿鲁加姆锡兰蛭(Zeylanicobdella arugamensis)的在体感染与生活史观察

阿鲁加姆锡兰蛭(Zeylanicobdella arugamensis)是重要的鱼类体外寄生虫,可感染30余种海水鱼类.阿鲁加姆锡兰蛭病在我国和东南亚多个国家的海水养殖鱼类中流行,严重时可导致鱼类大量死亡.为持续、稳定、足量地获得活体寄生虫,供防治鱼蛭病研究使用,本研究通过鱼蛭在体感染实验,建立了阿鲁加姆锡兰蛭的传代培...     

The impact of Anguillicola crassus on European eels

The impact of the parasitic swimbladder nematode, Anguillicola crassus Kuwahara, Niimi & Itagaki, on European eel populations is assessed with reference to published research on its origin and rapid dissemination, life cycle and transmission dynamics, and its pathogenic effect. The parasite was originally endemic to East Asia, but has transferred from its native host, the Japanese eel, Anguilla japonica Temminck & Schlegel, to the European eel, Anguilla anguilla (L.) and American eel, Anguilla rostrata (Le Seur). Anguillicola crassus is a very successful colonizer and is now known to occur in four continents (Asia, Europe, Africa and America). The nematode can severely impair swimbladder function and has caused mortalities in both farmed and wild populations in the presence of other stressors. Anguillicola crassus may impair the capacity of European eels to complete the spawning migration, although direct evidence is not available to support this hypothesis. Areas for future research are recommended.     

Prevalence and Species Identity of Trypanorhyncha in Cultured and Wild Amberjack,Seriola spp. in Hawaii – Implications for Aquaculture

The advent of molecular technologies allow for identification of organisms that were previously challenging or not possible. Conventional polymerase chain reaction analyses of a segment of the small subunit ribosomal RNA gene from trypanorhynch plerocerci obtained from cultured and wild caught amberjacks, Seriola dumerili, and Seriola rivoliana of the family Carangidae from Hawai‘i and Japan were found to be 100% identical, indicating that the cestodes from Japan and Hawai‘i are the same species, Protogrillotia zerbiae. The prevalence of the trypanorhynch plerocerci found in the musculature of Hawai‘i wild‐caught S. dumerili and S. rivoliana was 86.9 and 72.7%, respectively. In stark contrast, no trypanorhynch plerocerci have been detected in S. rivoliana cultured in Hawai‘i and they are only rarely seen in S. dumerili cultured in Japan. Trypanorhynch plerocerci are part of a complex life cycle that involves the transmission in at least two intermediate hosts before finally residing in a host shark species. The results of this study indicate that artificial propagation of the amberjacks using manipulated diets has most likely disrupted the life cycle of this tapeworm, thus reducing the prevalence of this parasite in farmed amberjacks and enhancing the marketability of cultured amberjack.     

Host‐specificity of the endangered thick‐shelled river mussel (Unio crassus,Philipsson 1788) and implications for conservation

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Potential environmental effects of probiotics used in aquaculture

Probiotics are a live microbial feed supplement that beneficially affects the host animal. As aquaculture is one of the main areas where probiotics can be applied, the environmental suitability of using probiotics in hatching and nursing facilities for turbot farming was evaluated through the life cycle assessment (LCA) methodology. This LCA study showed that the potential environmental impacts associated with probiotic production are generally offset by the impact reductions linked to lower consumption levels and reduced waste and emission generation rates within the hatching and nursing subsystem. Thus, the use of probiotics is recommended in order to enhance the performance of turbot aquaculture systems provided that operational and economic advantages are attained.     

Stable isotopes reveal the importance of terrestrially derived resources for the diet of the freshwater pearl mussel (Margaritifera margaritifera)

1. The freshwater pearl mussel (FPM) is among the most endangered freshwater species worldwide. The few remaining populations suffer from low recruitment rates and are subject to habitat fragmentation, pollution, siltation, decline or loss of host fish populations, and climate change.
2. Successful conservation strategies for FPM require a holistic understanding of its ecological requirements, life history, population dynamics, and habitat prerequisites. Although habitat requirements are well described, food requirements at different life stages have received less attention.
3. Stable isotope analyses of FPM and potential food resources in three German streams were combined with mixing model analysis to quantify organic matter resources assimilated by juvenile (first year after encystment from host fish) and semi-adult (10 years old, immature) individuals.
4. There were only slight differences in dietary contributions between the two life stages, and terrestrial particulate organic matter and benthic organic matter contributed substantially to the diet. Tissue type was more important in explaining variation in dietary contributions than individual variation for semi-adult FPM. The strong reliance on terrestrial resources sheds new light on the functional role of unionid mussels and the connection of streams to their riparian area.
5. The dependence of FPM on terrestrial resources also emphasizes the need for a stronger focus on the restoration and protection of intact riparian areas, including wetlands with their specific vegetation, when planning conservation and management strategies for threatened FPM populations.