This paper reviews current knowledge of the structure, genesis, cytochemistry and putative functions of the haplosporosomes of haplosporidians (Urosporidium, Haplosporidium, Bonamia, Minchinia) and paramyxids (Paramyxa, Paramyxoides, Marteilia, Marteilioides, Paramarteilia), and the sporoplasmosomes of myxozoans (Myxozoa - Malacosporea, Myxosporea). In all 3 groups, these bodies occur in plasmodial trophic stages, disappear at the onset of sporogony, and reappear in the spore. Some haplosporidian haplosporosomes lack the internal membrane regarded as characteristic of these bodies and that phylum. Haplosporidian haplosporogenesis is through the Golgi (spherulosome in the spore), either to form haplosporosomes at the trans-Golgi network, or for the Golgi to produce formative bodies from which membranous vesicles bud, thus acquiring the external membrane. The former method also forms sporoplasmosomes in malacosporeans, while the latter is the common method of haplosporogenesis in paramyxids. Sporoplasmogenesis in myxosporeans is largely unknown. The haplosporosomes of Haplosporidium nelsoni and sporoplasmosomes of malacosporeans are similar in arraying themselves beneath the plasmodial plasma membrane with their internal membranes pointing to the exterior, possibly to secrete their contents to lyse host cells or repel haemocytes. It is concluded that these bodies are probably multifunctional within and between groups, their internal membranes separating different functional compartments, and their origin may be from common ancestors in the Neoproterozoic.

This paper provides the first detailed description of a Tetracapsuloides species, Tetracapsuloides vermiformis n. sp., with vermiform stages in the bryozoan host, Fredericella sultana, and its experimental transmission from F. sultana to Cyprinus carpio. The suitability of morphological, biological and 18S rDNA sequence data for discrimination between malacosporean species is reviewed and recommendations are given for future descriptions. Presently, malacosporean species cannot be differentiated morphologically due to their cryptic nature and the lack of differential characters of spores and spore-forming stages in both hosts. We examined biological, morphological and molecular characters for the present description and for revising malacosporean taxonomy in general. As a result, Buddenbrockia plumatellae was split into two species, with its sac-like stages being ascribed to Buddenbrockia bryozoides n. comb. In addition to ribosomal DNA sequences multiple biological features rather than morphological characters are considered essential tools to improve malacosporean taxonomy in the future according to our analysis of the limited traits presently available.

The extraction of energy from the coastal ocean by arrays of tidal turbines has the potential to impart a variety of environmental effects. A primary area of interest for marine energy has been the Pentland Firth in the north of Scotland, and its subsidiary channel the Inner Sound, where tidal current speeds regularly reach 5 m s. One of the potential impacts of energy extraction is on local sediment dynamics Accurate sediment transport modelling is inhibited by a lack of detailed knowledge of local sediment deposits and transport in the area, but information on local sediment distributions in the Inner Sound is gradually being accumulated through multibeam [1] and sidescan sonar surveys [2,3]. Sediment banks are known to lie to the south of the island of Stroma but the local sediment dynamics, and the potential impacts of tidal energy extraction on the deposits, are only beginning to be understood. McIlvenny et al. [2] suggested that the local sediment banks in the Inner Sound have been locked in place for a significant period of time, with rates of sediment erosion and deposition expected to be low over the period. The tidal current velocities and the bed shear stress fields calculated by [2] using a 2D hydrodynamic model were largely consistent with the observed sediment distributions, with sediment banks lying adjacent to the main flow through the Inner Sound. However, depth-averaged modelled velocities, as used by [2], cannot be considered ideal to calculate bed shear stress fields. In the current absence of real world commercial arrays, accurate and robust hydrodynamic models are an important tool to predict potential effects on the ambient environment prior to array development. In this presentation, we apply a three-dimensional (3D) hydrodynamic model [4] to consider the potential effects of energy extraction by an array of tidal turbines on the ambient flow and local bed shear stress in the Inner Sound of the Pentland Firth. Bed shear stress is a key parameter in the erosion of seabed sediment. Building on the 2D modelling work reported by [2], we extend the modelling study to 3D, thereby resolving the vertical structure of the flow and leading to better estimates of near-bed velocity and local bed shear stress during flood and ebb tides, and allowing better predictions of the potential changes to bed shear stress following the installation of tidal turbines. The model solves the Reynold-averaged NavierStokes equations on an unstructured mesh using mixed finite element and finite volume techniques. Individual tidal turbines are represented through an additional form drag term in the momentum balance equation. The thrust imparted and power generated by the turbines is velocity dependent, with appropriate cut-in and cut-out velocities. In the presentation, we describe the model, its application to the Inner Sound, and present some numerical predictions of the effects of introducing a tidal turbine array into the area.

Discarding by fisheries is perceived as contrary to responsible harvesting. Legislation seeking to end the practice is being introduced in many jurisdictions. However, discarded fish are food for a range of scavenging species; so, ending discarding may have ecological consequences. Here we investigate the sensitivity of ecological effects to discarding policies using an ecosystem model of the North Sea—a region where 30–40% of trawled fish catch is currently discarded. We show that landing the entire catch while fishing as usual has conservation penalties for seabirds, marine mammals and seabed fauna, and no benefit to fish stocks. However, combining landing obligations with changes in fishing practices to limit the capture of unwanted fish results in trophic cascades that can benefit birds, mammals and most fish stocks. Our results highlight the importance of considering the broader ecosystem consequences of fishery management policy, since species interactions may dissipate or negate intended benefits.

Comprehensive analysis of parameter and driver sensitivity is key to establishing the credibility of models representing complex systems. This is especially so for models of natural systems where experimental manipulation of the real-world to provide controlled validation data is not possible. End-to-end ecosystem models (nutrients to birds and mammals) of marine ecosystems fall into this category with applications for evaluating the effects of climate change and fishing on nutrient fluxes and the abundances of flora and fauna. Here we present results of both ‘one-at-a-time’ (OAT) and variance based global sensitivity analyses (GSA) of the fish and fishery aspects of StrathE2E, an end-to-end ecosystem model of the North Sea. The sensitivity of the model was examined with respect to internal biological parameters, and external drivers related to climate and human activity. The OAT Morris method was first used to screen for factors most influential on model outputs. The Sobol GSA method was then used to calculate quantitative sensitivity indices. The results indicated that the fish and shellfish components of the model (demersal and pelagic fish, filter/deposit and scavenge/carnivore feeding benthos) were influenced by different sets of factors. Harvesting rates were highly influential on demersal and pelagic fish biomasses. Suspension/deposit feeding benthos were directly sensitive to changes in temperature, while the temperature acted indirectly on pelagic fish through the connectivity between model components of the food web. Biomass conversion efficiency was the most important factor for scavenge/carnivorous feeding benthos. The results indicate the primacy of fishing as the most important process affecting total fish biomass, together with varying responses to environmental factors which may be relevant in the context of climate change. The non-linear responses and parameter interactions identified by the analysis also highlight the necessity to use global rather than local methods for the sensitivity analysis of ecosystem models.

The phylum Myxozoa is composed of endoparasitic species that have predominately been recorded within aquatic vertebrates. The simple body form of a trophic cell containing other cells within it, as observed within these hosts, has provided few clues to relationships with other organisms. In addition, the placement of the group using molecular phylogenies has proved very difficult, although the majority of analyses now suggest that they are cnidarians. There have been relatively few studies of myxozoan stages within invertebrate hosts, even though these exhibit multicellular and sexual stages that may provide clues to myxozoan evolution. Therefore an ultrastructural examination of a myxozoan infection of a freshwater oligochaete was conducted, to reassess and formulate a model for myxozoan development in these hosts. This deemed that meiosis occurs within the oligochaete, but that fertilisation is not immediate. Rather, the resultant haploid germ cell (oocyte) is engulfed by a diploid sporogonic cell (nurse cell) to form a sporoplasm. It is this sporoplasm that infects the fish, resulting in the multicellular stages observed. Fertilisation occurs after the parasites leave the fish and enter the oligochaete host. The nurse cell/oocyte model explains previously conflicting evidence in the literature regarding myxosporean biology, and aligns phenomena considered distinctive to the Myxozoa, such as endogenous budding and cell within cell development, with processes recorded in cnidarians. Finally, the evolutionary origin of the Myxozoa as cnidarian parasites of ova is hypothesised.

Journal of Fish DiseasesVolume 35, Issue 12 p. 941-944 Short Communication Towards an in vitro culture method for the rainbow trout pathogen Tetracapsuloides bryosalmonae D J Morris, Corresponding Author D J Morris Institute of Aquaculture, University of Stirling, Stirling, UKCorrespondenceD J Morris, Department of Maths and Statistics, University of Strathclyde, Glasgow G1 1XH, UK (e-mail: [email protected])Search for more papers by this author D J Morris, Corresponding Author D J Morris Institute of Aquaculture, University of Stirling, Stirling, UKCorrespondenceD J Morris, Department of Maths and Statistics, University of Strathclyde, Glasgow G1 1XH, UK (e-mail: [email protected])Search for more papers by this author First published: 23 August 2012 https://doi.org/10.1111/j.1365-2761.2012.01421.xCitations: 3Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat References Bettge K., Segner H., Burki R., Schmidt-Posthaus H. & Wahli T. (2009) Proliferative kidney disease (PKD) of rainbow trout: temperature- and time-related changes of Tetracapsuloides bryosalmonae DNA in the kidney. Parasitology 136, 615–625. 10.1017/S0031182009005800 CASPubMedWeb of Science®Google Scholar Cheng L.-L., Browser P.R. & Spitsbergen J.M. (1993) Development of cell cultures derived from lake trout liver and kidney in a hormone supplemented serum reduced media. Journal of Aquatic Animal Health 5, 119–126. 10.1577/1548-8667(1993)005<0119:DOCCDF>2.3.CO;2 Google Scholar Clifton-Hadley R.S., Bucke D. & Richards R.H. (1987) A study of the sequential, clinical and pathological changes during proliferative kidney disease in rainbow trout, Salmo gairdneri Richardson. Journal of Fish Diseases 10, 335–352. 10.1111/j.1365-2761.1987.tb01081.x Web of Science®Google Scholar Freshney R.I. 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European Association of Fish Pathologists- EAFP, Rhodes. Google Scholar Okamura B., Hartikainen H., Schmidt-Posthaus H. & Wahli T. (2011) Life cycle complexity, environmental change and the emerging status of salmonid proliferative kidney disease. Freshwater Biology 56, 735–753. 10.1111/j.1365-2427.2010.02465.x Web of Science®Google Scholar Palenzuela O., Sitja-Bobadilla A. & Alvarez-Pellitero P. (1994) In vitro sporulation of Ceratomyxa sp. (Myxosporea: Bivavulida) from Sparus aurata L. (Teleostei: Sparidae). In: ICOPA VIII, Abstracts Book, Vol. 1, p. 195. Turkish Society for Parasitology, Izmir. Google Scholar Petchsupa N. (2002) Studies on Proliferative Kidney Disease with Particular Reference to Vaccine Development. PhD thesis, University of Stirling, UK. Google Scholar Redondo M.J., Palenzeula O. & Alverez-Pellitero P. (2003) In vitro studies on viability and proliferation of Enteromyxum scopthalmi (Myxozoa), an enteric parasite of cultured turbot Scopthalmus maximus. 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Journal of Fish Biology 73, 2184–2197. 10.1111/j.1095-8649.2008.02054.x Web of Science®Google Scholar Wolf K. & Markiw M.E. (1976) Myxosoma cerebralis: in vitro sporulation of the myxosporidian of salmonid whirling disease. Journal of Protozoology 23, 425–427. 10.1111/j.1550-7408.1976.tb03801.x PubMedWeb of Science®Google Scholar Yokoyama H. & Yutaka F. (1999) In vitro sporulation of Myxobolus spirosulcatus and Ceratomyxa spp. (Myxozoa: Myxosporea) infecting the gallbladder of yellowtail Seriola quinqueradiata. In: EAFP Ninth International Conference ‘Diseases of Fish and Shellfish’, p. 20. European Association of Fish Pathologists, Rhodes. Web of Science®Google Scholar Citing Literature Volume35, Issue12December 2012Pages 941-944 ReferencesRelatedInformation

Over the past 50 years, the culture of aquatic species in controlled conditions to enhance production has grown in importance and now provides nearly 50% of the world's seafood supply. In part, this expansion has been made possible by the use of antibiotics, antifungals, and other veterinary medicines to control disease and improve welfare. Despite guidelines being available, the sampling programmes for drug residue surveillance of aquaculture products recommended by the CODEX Alimentarius Commission were withdrawn in 2008 and put under review. Directive 96/23/EC sets out legislation to govern how sampling programmes for drug residue surveillance should be conducted within the EU. This directive applies both to produce raised within the EU and also imported products from third countries. This communication examines the existing EU sampling regimen for aquaculture products and comments on its possible application in a global context. We examine UK statutory sampling data that, while indicating the effectiveness of the directive, also suggests that the directive may lead to unnecessary sampling. Regarding imports, examination of the Rapid Alert System for Food and Feed (RASFF) database using process control charts and statistical modelling suggests that the sampling regimen described in the directive is effective but not sufficiently flexible for the range of aquaculture practices that exist. Limitations of the directive, datasets, and practices are further discussed. © 2012 John Wiley & Sons, Ltd.

This paper is a brief introduction to epidemiology and its application to farmed fish health and welfare with examples from the United Kingdom. Epidemiology has the potential to do a great deal more than just identify risk factors. Indeed in many cases useful risk factors cannot be identified due to the complexity of the disease problems and the lack of resources. Epidemiological principles or analytical techniques have been applied in animal welfare studies, and they can reduce the cost of disease monitoring or surveillance and disease control. However, for epidemiological studies to make a real contribution to farmed fish health and welfare it is often necessary to use multi-disciplinary teams, obtain good data and coordinate efforts on the major problems.

Eukaryotes form new cells through the replication of nuclei followed by cytokinesis. A notable exception is reported from the class Myxosporea of the phylum Myxozoa. This assemblage of approximately 2310 species is regarded as either basal bilaterian or cnidarian, depending on the phylogenetic analysis employed. For myxosporeans, cells have long been regarded as forming within other cells by a process referred to as endogenous budding. This would involve a nucleus forming endoplasmic reticulum around it, which transforms into a new plasma membrane, thus enclosing and separating it from the surrounding cell. This remarkable process, unique within the Metazoa, is accepted as occurring within stages found in vertebrate hosts, but has only been inferred from those stages observed within invertebrate hosts. Therefore, I conducted an ultrastructural study to examine how internal cells are formed by a myxosporean parasitizing an annelid. In this case, actinospore parasite stages clearly internalized existing cells; a process with analogies to the acquisition of endosymbiotic algae by cnidarian species. A subsequent examination of the myxozoan literature did not support endogenous budding, indicating that this process, which has been a central tenet of myxozoan developmental biology for over a century, is dogma.

All of the actinospore releasing oligochaetes collected in an environmental sample were found to be infected with the microsporidian Neoflabelliforma aurantiae n. gen. n. sp. Ultrastructural and phylogenetic studies on this microsporidian indicated similarities with Flabelliforma magnivora but not with the type species Flabelliforma montana, necessitating the formation of a new genus Neoflabelliforma and reassignment of F. magnivora as Neoflabelliforma magnivora n. comb. The development of N. aurantiae is described both parasitising the oligochaete worm and hyperparasitising the concurrent myxosporean infection. The effect of N. aurantiae on the myxosporeans was deleterious and progressive, eventually stopping all actinospore formation. Its discovery has the potential to impact on areas examining the phase of myxosporean life cycles in the invertebrate host, from transmission studies and epidemiology to re-evaluating the basic steps of intra-oligochaete development. Recent evidence has suggested that studies using invertebrate systems should consider possible adverse effects that co-infections can have on experimental outcomes. The discovery of N. aurantiae highlights the need for careful screening of experimental animals to help circumvent erroneous results.

ABSTRACT. A recent investigation into the myxozoan fauna of common gobies, Pomatoschistus microps, from the Forth Estuary in Scotland, revealed numerous myxosporean cysts within the gill cartilage. They were composed of polysporous plasmodia containing myxobolid spores that were morphologically different from the other known species of Myxobolus and from the myxosporeans previously recorded from this host (i.e. the ceratomyxid Ellipsomyxa gobii, infecting the gall bladder, and the kudoid Kudoa camarguensis, infecting the muscle tissues). Spores were ovoid, 9.4 × 9.1 μm with a thickness of 6.6 μm, with two pyriform polar capsules, the polar filaments of which had four to five turns. Molecular analysis of the parasite's small subunit rDNA region, based upon a contiguous sequence of 1,558 base pairs, discriminated it from other myxosporean species that have been characterized so far. A comparison of the spore morphology and the molecular sequences determined for this new isolate with other myxozoans described to date, confirmed its identity as a previously unknown myxobolid supporting the proposal that this isolate be elevated to the species level as a new species within the genus Myxobolus. A phylogenetic analysis places this new myxobolid, Myxobolus albi n. sp., in a basal position of a clade containing the majority of Henneguya spp. sequenced to date and various Myxobolus spp.

SUMMARY Tetracapsuloides bryosalmonae is the myxozoan that causes the commercially and ecologically important proliferative kidney disease of salmonid fish species. Immunohistochemistry and electron microscopy were used to examine the development of this parasite within the kidney of the brown trout Salmo trutta. The main replicative phase of T. bryosalmonae is a cell doublet composed of a primary cell and a single secondary cell. Engulfment of one secondary cell by another to form a secondary-tertiary doublet (S-T doublet) heralded the onset of sporogony whereupon the parasite migrated to the kidney tubule lumen. Within the tubule, the parasite transformed into a pseudoplasmodium and anchored to the tubule epithelial cells via pseudopodial extensions. Within each pseudoplasmodium developed a single spore, composed of 4 valve cells, 2 polar capsules and 1 sporoplasm. The pseudoplasmodia formed clusters suggesting that large numbers of spores develop within the fish. This examination of T. bryosalmonae suggests that the main replicative phase of freshwater myxozoans within vertebrates is via direct replication of cell doublets rather than through the rupturing of extrasporogonic stages, while tertiary cell formation relates only to sporogony. Taken in conjunction with existing phylogenetic data, 5 distinct sporogonial sequences are identified for the Myxozoa.

Tetracapsuloides bryosalmonae is the myxozoan parasite responsible for proliferative kidney disease (PKD) of salmonid fishes. This disease affects farmed species in North America and Western Europe where it results in significant economic losses for the rainbow trout industry. The parasite has two hosts in its life cycle, salmonid fish, and freshwater bryozoans. In this study, we describe the development of the parasite at the ultrastructural level within the bryozoan host Fredericella sultana. Single celled, presaccular stages form aggregates within the metacoel of this host which resolve into spore sacs. Within these sacs sporogenesis is initiated with the differentiation of presporogonic cells into sporogonic and valvogenic cells. These latter cells surround a sporogonic cell which subsequently divides to form a sporoplasmogenic cell and a capsulogenic cell. The capsulogenic cell divides further to form four cells each with a polar capsule, while the sporoplasmogenic cell divides resulting in four cells, two primary cells and two secondary cells. The secondary cells are engulfed by the primary cells resulting in a mature sporoplasm. It is hypothesized that autogamy occurs during the initial formation of the spore sac and that allogamy is also possible during this time.

Members of the phylum Myxozoa are obligate parasites, primarily of aquatic organisms. Their phylogeny has remained problematic, with studies placing them within either the Bilateria or Cnidaria. The discovery that the enigmatic Buddenbrockia plumatellae is a myxozoan that possesses distinct bilaterian features appeared to have finally resolved the debate. B. plumatellae is described as a triploblastic ‘worm-like’ organism, within which typical myxozoan malacospores form. Using EM we examined the early development of the B. plumatellae ‘worms’ within the bryozoan host Plumatella repens. The initial development involved numerous unicellular, amoeboid pre-saccular stages that were present within the basal lamina of the host’s body wall. These stages migrate immediately beneath the peritoneum where a significant host tissue reaction occurs. The stages aggregate, initiating the formation of a ‘worm’. The base of a developing ‘worm’ forms a pseudosyncytium which resolves into an ectoderm surrounding a mesendoderm. The pseudosyncytium is directly anchored into neighbouring host cells via masses of striated fibres. The replication of the ectodermal and mesendodermal cells extends the developing ‘worm’ into the coelom of the host. The mesendoderm resolves to form a mesoderm and an endoderm. Myogenesis appears to be initiated from the anchored end of the ‘worm’ and develops along the mesoderm. The aggregation and differentiation of amoeboid pre-saccular stages to initiate the ‘worm’ draws analogies to the sacculogenesis observed for Tetracapsuloides bryosalmonae, B. plumatellae’s sister taxon within the class Malacosporea. The development of a multicellular, spore forming organism, from single cells does not correlate to any bilaterian or cnidarian species. Current phylogenies indicate the Myxozoa are basal bilaterians along with the Acoela and Mesozoa. Comparison with these other basal groups may help to resolve the placement of Myxozoa within the tree of life.

Proliferative kidney disease (PKD), caused by the malacosporean parasite, Tetracapsuloides bryosalmonae, is a major disease of salmonid culture both in western Europe and North America. The fish are infected from spores that develop within freshwater bryozoans and are released into the water column. Although sporogenesis has been studied in the bryozoan host and occurs within sacs, the formation of these sacs from presaccular stages has only been hypothesized. Examination of infected bryozoans by using a range of techniques identified proliferating, presaccular amoeboid stages of T bryosalmonae on the body wall of the bryozoan Fredericella sultana. These stages possessed unique electron-dense bodies and were observed as aggregating within the bryozoan metacoel, differentiating to form spore sacs. Spore sac growth was associated with the assimilation of the presaccular parasites rather than through cryptomitosis of sac mural cells. This sac formation through aggregation and assimilation suggests an intriguing mechanism by which T. bryosalmonae can cross-fertilize.

Species of the phylum Myxozoa are common parasites of fish and can cause severe losses in cultured species. Although a number of myxozoan life-cycles have now been elucidated, little is known about the biology of these organisms in the fish host. Monoclonal antibody B4 raised to the myxozoanTetracapsuloides bryosalmonaehas been previously noted to react with a number of species infecting fish kidney. We present the results of a survey of 55 myxosporean species that determined that this antibody detects an antigen on the spore surface of 33 of these species in the generaMyxobolus,SphaerosporaandThelohanellus. However, there appears to be no clear relationship between those spores that contain the MAb B4 reactive antigen and the host or organ in which they are detected. The antigen appears to be synthesized in the plasmodial cytoplasm and is intimately associated with the surface of the spore capsules and, where present, the mucus envelope. The nature of this envelope is further discussed in relation to its formation and distinctive properties.

The myxozoan parasite Tetracapsuloides bryosalmonae is the causative agent of proliferative kidney disease (PKD), a highly damaging disease of cultured salmonid fish. Within this study, phylactolaemate bryozoans were collected from a river known to be endemic for PKD and subsequently cultured in the laboratory. Sequential developmental stages of T. bryosalmonae were studied by light microscopy within the living bryozoan colonies, allowing the identification of stages attached to host peritoneum, consistent with previous molecular evidence of cryptic stages. Infection resulted in the production of large numbers of spores, which were released from the bryozoans. Experimental exposure of rainbow trout (Oncorhynchus mykiss) to medium in which infected bryozoans were cultured resulted in clinical PKD. Rainbow trout were exposed to known numbers of T. bryosalmonae spores collected by micromanipulation, which had been released from mature spore sacs within colonies of the bryozoan Fredericella sultana. Exposure to one spore was sufficient to lead to development of PKD. These findings indicate that small numbers of bryozoans are capable of releasing sufficient spores to infect large numbers of fish, having implications for future control methods for PKD in salmonid farming.