The use of Atlantic hagfish (Myxine glutinosa) as a bioindicator species for studies on effects of dumped chemical warfare agents in the Skagerrak. 1: Liver histopathology.

Within the framework of the international project DAIMON (Decision Aid for Marine Munitions), the impact of dumped chemical munitions on fish health was investigated. The Skagerrak Straight (North Sea, at 600 m depth) contains munitions with chemical warfare agents (CWA), scuttled after the end of World War II. Studies of liver histopathology in Atlantic hagfish (Myxine glutinosa) were carried out at three sampling sites: at a wreck with CWA in the Skagerrak (n = 82), a Skagerrak reference site considered to be free of CWA (n = 14) and at a reference site in the northern North Sea outside the Skagerrak (n = 17). Liver lesions were diagnosed and categorized according to standardized ICES and BEQUALM protocols and OSPAR guidelines. Non-specific liver lesions were found in 87.6% of 113 hagfish examined. The prevalence of pre-neoplastic lesions was 7.1% and of neoplastic lesions 6.2%. There was no statistically significant difference in prevalence between hagfish samples from the wreck site and from the reference site near the wrecks. However, at the reference site in the northern North Sea, the prevalence of non-specific lesions was low and neither pre-neoplastic nor neoplastic lesions were observed.

The use of Atlantic hagfish (Myxine glutinosa) as a bioindicator species for studies on effects of dumped chemical warfare agents in the Skagerrak. 2. Biochemical biomarkers.

The sea bottom of the Skagerrak Strait (North Sea) contains munitions loaded with chemical warfare agents (CWA), mostly stored in shipwrecks scuttled intentionally after the end of the World War II. The munition shells inside the wrecks are in different states of deterioration and corrosion and their environmental risk potential is unknown. The Atlantic hagfish (Myxine glutinosa), a sediment-dwelling chordate, was used as a model organism to study the potential impact of dumped CWA on the local ecosystem by using biochemical biomarkers. The hagfish were collected in 2017 and 2018 at three sampling sites: in the immediate vicinity of a wreck with CWA in the Skagerrak, a few kilometres from the wreck, and a reference site 21 km from the wreck, considered to be free of CWA. Significant differences were observed between the wreck site and the reference sites in the activities of glutathione reductase, superoxide dismutase and glutathione S-transferase, while the activity levels of catalase and acetylcholinesterase were identical at all sites. The recorded differences demonstrated negative biological effects in the hagfish sampled close to the dumped chemical munitions. Due to the limited knowledge of hagfish biology and of the extent of CWA contamination in Skagerrak, the results presented here warrant more research to further elucidate the potential environmental risks of the scuttled wrecks. The usefulness of the species as a bioindicator organism is further discussed.

Haplosporosomes, sporoplasmosomes and their putative taxonomic relationships in rhizarians and myxozoans.

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.

Sustainable aquaculture through the One Health lens.

Aquaculture is predicted to supply the majority of aquatic dietary protein by 2050. For aquaculture to deliver significantly enhanced volumes of food in a sustainable manner, appropriate account needs to be taken of its impacts on environmental integrity, farmed organism health and welfare, and human health. Here, we explore increased aquaculture production through the One Health lens and define a set of success metrics - underpinned by evidence, policy and legislation - that must be embedded into aquaculture sustainability. We provide a framework for defining, monitoring and averting potential negative impacts of enhanced production - and consider interactions with land-based food systems. These metrics will inform national and international science and policy strategies to support improved aquatic food system design.

The aquatic animal pandemic crisis.

The growth of aquaculture over the past 50 years has been accompanied by the emergence of aquatic animal diseases, many of which have spread to become pandemic in countries or continents. An analysis of 400 emerging disease events in aquatic animals that were logged by the Centre for Environment, Fisheries and Aquaculture Science between 2002 and 2017 revealed that more than half were caused by viruses. However, in molluscs, most events were parasitic. Categorising these events indicated that the key processes underpinning emergence were the movement of live animals and host switching. Profiles of key pathogens further illustrate the importance of wild aquatic animals as the source of new infections in farmed animals. It is also clear that the spread of new diseases through the largescale movement of aquatic animals for farming, for food and for the ornamental trade has allowed many to achieve pandemic status. Many viral pathogens of fish (e.g. infectious salmon anaemia, viral haemorrhagic septicaemia) and shrimp (e.g. white spot syndrome virus) affect a large proportion of the global production of key susceptible species. Wild aquatic animal populations have also been severely affected by pandemic diseases, best exemplified by Batrachochytrium dendrobatidis, a fungal infection of amphibians, whose emergence and spread were driven by the movement of animals for the ornamental trade. Batrachochytrium dendrobatidis is now widespread in the tropics and subtropics and has caused local extinctions of susceptible amphibian hosts. Given the rising demand for seafood, aquacultural production will continue to grow and diseases will continue to emerge. Some will inevitably achieve pandemic status, having significant impacts on production and trade, unless there are considerable changes in global monitoring and the response to aquatic animal diseases.

Au cours des 50 dernières années, la forte croissance qu'a connue l'aquaculture est allée de pair avec l'émergence de nombreuses maladies affectant les animaux aquatiques, dont certaines se sont propagées jusqu'à devenir pandémiques à l'échelle nationale ou continentale. L'analyse de 400 événements sanitaires survenus chez des animaux aquatiques et consignés entre 2002 et 2017 par le Centre for Environment, Fisheries and Aquaculture Science a déterminé l'origine virale de plus de la moitié d'entre eux. Toutefois, chez les mollusques la plupart des événements analysés étaient d'ordre parasitaire. Le classement des événements par catégories a montré que les principaux processus sous-jacents à cette émergence étaient liés aux transferts d'animaux vivants et à la colonisation de nouveaux hôtes par les agents pathogènes. Les profils des agents pathogènes majeurs illustrent le rôle des espèces aquatiques sauvages en tant que sources d'infections nouvelles chez les animaux aquatiques d'élevage. Il apparaît clairement que la propagation de nouvelles maladies à la faveur des transferts massifs d'animaux aquatiques à des fins d'élevage, de production alimentaire ou de commerce d'espèces d'ornement a conféré un statut pandémique à nombre de ces maladies. De nombreux virus affectant les poissons (par ex., le virus de l'anémie infectieuse du saumon, le virus de la septicémie hémorragique virale) et les crevettes (par ex., le virus du syndrome des points blancs) ont une incidence majeure sur de vastes segments de la production mondiale d'espèces sensibles cruciales. Les populations sauvages d'animaux aquatiques sont également touchées par des maladies pandémiques, dont l'exemple type est l'infection à Batrachochytrium dendrobatidis, une affection fongique des amphibiens dont l'émergence et la propagation sont le fruit des transferts d'animaux aquatiques destinés au commerce aquariophile. Batrachochytrium dendrobatidis est désormais largement présent dans les eaux tropicales et subtropicales où il est responsable d'extinctions locales parmi les espèces d'amphibiens sensibles. La croissance de la production aquacole se poursuivra afin de répondre à une demande toujours plus forte en poissons et fruits de mer, entraînant l'émergence continue de nouvelles maladies. Si des changements déterminants ne sont pas introduits dans la surveillance exercée au niveau mondial sur les maladies des animaux aquatiques et dans la réponse qui leur est apportée, certaines de ces maladies vont inéluctablement acquérir une dimension pandémique avec des conséquences importantes sur la production et le commerce.

El crecimiento de la acuicultura en los últimos 50 años se ha acompañado de la aparición de enfermedades de los animales acuáticos, que en muchos casos se han propagado hasta llegar a ser pandémicas en ciertos países o continentes. Tras analizar 400 episodios de enfermedades emergentes de animales acuáticos registrados entre 2002 y 2017 por el Centre for the Environment, Fisheries and Aquaculture Science, los autores constataron que más de la mitad de esos episodios fueron causados por virus, si bien en el caso de los moluscos la mayoría de ellos eran parasitarios. De la clasificación de esos episodios se desprende que los procesos básicos que subyacen a su aparición son los desplazamientos de animales vivos y los cambios de anfitrión. El perfil de los principales patógenos revela además la importancia que revisten los animales acuáticos silvestres como fuente de nuevas infecciones de los animales de acuicultura. También está claro que la propagación de nuevas enfermedades por el movimiento a gran escala de animales acuáticos con fines de producción acuícola, consumo alimentario o comercio de animales ornamentales ha propiciado que muchas de ellas adquieran carácter pandémico. Muchos patógenos víricos de los peces (como el virus de la anemia infecciosa del salmón o el de la septicemia hemorrágica viral) y camarones (como el virus del síndrome de las manchas blancas) afectan a una gran parte de la producción mundial de las principales especies sensibles. Las poblaciones silvestres de animales acuáticos también se han visto afectadas de gravedad por enfermedades pandémicas, como ejemplifica perfectamente la infección por Batrachochytrium dendrobatidis, micosis de los anfibios cuya aparición y propagación fue alimentada por el comercio y el consiguiente movimiento de animales con fines ornamentales. Este hongo, muy extendido ahora en las regiones tropicales y subtropicales, ha causado la extinción en ciertas áreas de especies anfibias sensibles. Habida cuenta de la creciente demanda de alimentos de origen marino, la producción acuícola seguirá creciendo y también seguirán surgiendo enfermedades. Inevitablemente, algunas de ellas se harán pandémicas y resultarán muy dañinas para la producción y el comercio, a menos que haya cambios de calado en los sistemas mundiales de vigilancia y respuesta ante las enfermedades de los animales acuáticos.

Marteilia refringens and Marteilia pararefringens sp. nov. are distinct parasites of bivalves and have different European distributions.

Marteilia refringens causes marteiliosis in oysters, mussels and other bivalve molluscs. This parasite previously comprised two species, M. refringens and Marteilia maurini, which were synonymized in 2007 and subsequently referred to as M. refringens 'O-type' and 'M-type'. O-type has caused mass mortalities of the flat oyster Ostrea edulis. We used high throughput sequencing and histology to intensively screen flat oysters and mussels (Mytilus edulis) from the UK, Sweden and Norway for infection by both types and to generate multi-gene datasets to clarify their genetic distinctiveness. Mussels from the UK, Norway and Sweden were more frequently polymerase chain reaction (PCR)-positive for M-type (75/849) than oysters (11/542). We did not detect O-type in any northern European samples, and no histology-confirmed Marteilia-infected oysters were found in the UK, Norway and Sweden, even where co-habiting mussels were infected by the M-type. The two genetic lineages within 'M. refringens' are robustly distinguishable at species level. We therefore formally define them as separate species: M. refringens (previously O-type) and Marteilia pararefringens sp. nov. (M-type). We designed and tested new Marteilia-specific PCR primers amplifying from the 3' end of the 18S rRNA gene through to the 5.8S gene, which specifically amplified the target region from both tissue and environmental samples.

Evidence for trophic transfer of Inodosporus octospora and Ovipleistophora arlo n. sp. (Microsporidia) between crustacean and fish hosts.

Within aquatic habitats, the hyper-abundant Order Crustacea appear to be the predominant host group for members of the Phylum Microsporidia. The musculature, a common site of infection, provides access to biochemical (carbohydrate-rich) and physiological (mitochondria-rich) conditions conducive to prolific parasite replication and maturation. The significant proportion of body plan devoted to skeletal musculature in Crustacea provides the location for a highly efficient intracellular parasite factory. In this study, we utilize histological, ultrastructural and phylogenetic evidence to describe a previously known (Inodosporus octospora) and novel (Ovipleistophora arlo n. sp.) microsporidian parasites infecting the musculature of the common prawn (Palaemon serratus) from the same site, at the same time of year. Despite similar clinical signs of infection, both parasites are otherwise distinct in terms of pathogenesis, morphology and phylogeny. Based upon partial subunit ribosomal RNA (SSU rDNA) sequence, we show that that I. octospora may be identical to a Kabatana sp. previously described infecting two-spot goby (Gobiusculus flavescens) in Europe, or at least that Inodosporus and Kabatana genera are synonyms. In addition, SSU rDNA sequence for O. arlo places it within a distinct clade containing Ovipleistophora mirandellae and Ovipleistophora ovariae, both infecting the oocytes of freshwater fish in Europe. Taken together, our data provide strong evidence for trophic-transfer between crustacean and fish hosts for two different microsporidians within clade 5 of the phylum. Furthermore, it demonstrates that morphologically and phylogenetically distinct microsporidians can infect the same tissues of the same host species to impart clinical signs which mimic infection with the other.

Hyperspora aquatica n.gn., n.sp. (Microsporidia), hyperparasitic in Marteilia cochillia (Paramyxida), is closely related to crustacean-infecting microspordian taxa.

The Paramyxida, closely related to haplosporidians, paradinids, and mikrocytids, is an obscure order of parasitic protists within the class Ascetosporea. All characterized ascetosporeans are parasites of invertebrate hosts, including molluscs, crustaceans and polychaetes. Representatives of the genus Marteilia are the best studied paramyxids, largely due to their impact on cultured oyster stocks, and their listing in international legislative frameworks. Although several examples of microsporidian hyperparasitism of paramyxids have been reported, phylogenetic data for these taxa are lacking. Recently, a microsporidian parasite was described infecting the paramyxid Marteilia cochillia, a serious pathogen of European cockles. In the current study, we investigated the phylogeny of the microsporidian hyperparasite infecting M. cochillia in cockles and, a further hyperparasite, Unikaryon legeri infecting the digenean Meiogymnophallus minutus, also in cockles. We show that rather than representing basally branching taxa in the increasingly replete Cryptomycota/Rozellomycota outgroup (containing taxa such as Mitosporidium and Paramicrosoridium), these hyperparasites instead group with other known microsporidian parasites infecting aquatic crustaceans. In doing so, we erect a new genus and species (Hyperspora aquatica n. gn., n.sp.) to contain the hyperparasite of M. cochillia and clarify the phylogenetic position of U. legeri. We propose that in both cases, hyperparasitism may provide a strategy for the vectoring of microsporidians between hosts of different trophic status (e.g. molluscs to crustaceans) within aquatic systems. In particular, we propose that the paramyxid hyperparasite H. aquatica may eventually be detected as a parasite of marine crustaceans. The potential route of transmission of the microsporidian between the paramyxid (in its host cockle) to crustaceans, and, the 'hitch-hiking' strategy employed by H. aquatica is discussed.

Comparative pathology in bivalves: Aetiological agents and disease processes.

Comparative pathology as a scientific discipline studies animal diseases in relation to their aetiology, pathogenesis and prognosis. Among the main aspects of this discipline, regressive changes, host defense responses with pathological implications and progressive changes, represent the majority of the possible responses of cells and tissues to pathogens and exposure to chemicals. One of the most persistent issues in the field of invertebrate pathology is the variability in terminology and definition, which has led to confusion in scientific communication. The aim of this paper is to provide an overview of the pathological basis of bivalve disease (defensive, regressive and progressive phenomena) and contribute to the standardised terminology for bivalve molluscan disease in the context of comparative pathology.

Histopathological assessment of liver and gonad pathology in continental slope fish from the northeast Atlantic Ocean.

The deep-sea environment is a sink for a wide variety of contaminants including heavy metals and organic compounds of anthropogenic origin. Life history traits of many deep-water fish species including longevity and high trophic position may predispose them to contaminant exposure and subsequent induction of pathological changes, including tumour formation. The lack of evidence for this hypothesis prompted this investigation in order to provide data on the presence of pathological changes in the liver and gonads of several deep-water fish species. Fish were obtained from the north east region of the Bay of Biscay (north east Atlantic Ocean) by trawling at depths between 700 and 1400 m. Liver and gonad samples were collected on board ship and fixed for histological processing and subsequent examination by light microscopy. Hepatocellular and nuclear pleomorphism and individual cases of ovotestis and foci of cellular alteration (FCA) were detected in black scabbardfish (Aphanopus carbo). Six cases of FCA were observed in orange roughy (Hoplostethus atlanticus) (n = 50) together with a single case of hepatocellular adenoma. A wide variety of inflammatory and degenerative lesions were found in all species examined. Deep-water fish display a range of pathologies similar to those seen in shelf-sea species used for international monitoring programmes including biological effects of contaminants. This study has confirmed the utility of health screening in deep-water fish for detecting evidence of prior exposure to contaminants and has also gained evidence of pathology potentially associated with exposure to algal toxins.

An experimental means of transmitting pancreas disease in Atlantic salmon Salmo salar L. fry in freshwater.

A challenge model for pancreas disease in Atlantic salmon, Salmo salar L. fry, was developed comparing two salmonid alphavirus (SAV) subtypes: SAV1 and SAV5. Viral doses of 3 × 10(5) TCID50  mL(-1) for SAV1 and 3 × 10(4) for SAV5 were tested in triplicate tanks, each containing 450 salmon fry. Cumulative mortalities of 1.2% were recorded. Titres of virus recovered from the mortalities ranged from 10(2) to 10(7) TCID50  mL(-1) . Fry were sampled at 3, 5 and 7.5 weeks post-challenge. Sampling after 3 weeks revealed a high prevalence of infection in the absence of clinical signs, and infectious virus was recovered from 80% and 43% of sampled fry infected with SAV1 and SAV5, respectively. After 5 weeks pancreas, heart and red skeletal muscle lesions were generally observed, whilst degeneration in white skeletal muscle was observed only in fish infected with SAV1. In situ hybridisation confirmed the presence of viral genome in infected pancreas, heart and muscle. After 7.5 weeks, infectious virus (both isolates) was recovered from 13.3% of the fish sampled, with a viral titre of 10(2) TCID50  mL(-1) . Clearly, salmon fry are susceptible to SAV infection and pancreas disease.

Puffy skin disease (PSD) in rainbow trout, Oncorhynchus mykiss (Walbaum): a case definition.

Puffy skin disease (PSD) is a disease that causes skin pathology in rainbow trout, Oncorhynchus mykiss (Walbaum). Incidence of PSD in UK fish farms and fisheries has increased sharply in the last decade, with growing concern from both industry sectors. This paper provides the first comprehensive case definition of PSD, combining clinical and pathological observations of diseased rainbow trout from both fish farms and fisheries. The defining features of PSD, as summarized in the case definition, were focal lateral flank skin lesions that appeared as cutaneous swelling with pigment loss and petechiae. These were associated with lethargy, poor body condition, inappetance and low level mortality. Epidermal hyperplasia and spongiosis, oedema of the dermis stratum spongiosum and a mild diffuse inflammatory cellularity were typical in histopathology of skin. A specific pathogen or aetiology was not identified. Prevalence and severity of skin lesions was greatest during late summer and autumn, with the highest prevalence being 95%. Atypical lesions seen in winter and spring were suggestive of clinical resolution. PSD holds important implications for both trout aquaculture and still water trout fisheries. This case definition will aid future diagnosis, help avoid confusion with other skin conditions and promote prompt and consistent reporting.

Epidemiology of Bonamia in the UK, 1982 to 2012.

Bonamiasis, caused by Bonamia ostreae, was confirmed in native flat oysters Ostrea edulis L. in England in 1982. Hudson & Hill (1991; Aquaculture 93:279-285) documented investigations into the initial spread of the disease in wild and cultivated stocks of native oysters in the UK. They also described the controls that were initially applied to prevent the further spread of the pathogen. This paper reports on subsequent controls and associated monitoring applied in the UK and reports on the epidemiology of the disease in the 30 yr from 1982 to 2012. Bonamiasis remained confined to the zones in England as documented by Hudson & Hill (1991) until 2005, when it was confirmed in Lough Foyle, Northern Ireland. In 2006 it was found in 2 new areas, one in Wales and one in Scotland. Subsequent further spread to additional areas in all parts of the UK has resulted in 9 zones being currently designated as infected with the disease. In addition, a single oyster from one area has tested positive for the closely related B. exitiosa. In general, analysis of the results of the monitoring programme in England and Wales shows no clear trend in infection levels over time, although there has been an apparent decrease in the level of infection in some fishery areas. In an autumn sampling programme the highest levels of infection were detected in October.

Acute dermatitis in farmed trout: an emerging disease.

A new skin condition, known as puffy skin disease (PSD), emerged in farmed rainbow trout Oncorhynchus mykiss (Walbaum) in 2002. The number of new cases increased considerably from 2006. Clinical signs include white or grey skin patches, which become raised and red with excessive mucous production and scale loss. Fish are inappetant and lose condition. Histologically, the key feature is epithelial hyperplasia. We undertook a questionnaire study of trout farmers in England and Wales to investigate prevalence and risk factors. PSD was reported on 37% (n = 49) of rainbow trout sites, located in 28 river catchments. The increase in cases from 2006 onwards was mirrored by the increase in red mark syndrome (RMS). Prevalence and severity of PSD were highest in the summer months. The presence of PSD was associated with RMS (OR = 9.7, P < 0.001). Sites receiving live rainbow trout in the previous 12 months were considerably more likely to have PSD (OR = 5.3. P < 0.01), which suggests an infectious aetiology. The size of affected fish and prevalence varied between farms, indicating that farm-level factors are important. Future research should further investigate the aetiology of PSD and practices to manage the disease.

Areospora rohanae n.gen. n.sp. (Microsporidia; Areosporiidae n. fam.) elicits multi-nucleate giant-cell formation in southern king crab (Lithodes santolla).

This paper utilises histological, ultrastructure and molecular phylogenetic data to describe a novel genus and species (Areospora rohanae n.gen., n.sp.) within the phylum Microsporidia. Phylogenetic and morphological distinction from other known lineages within the phylum also provide strong support for erection of a new family (Areosporiidae n. fam) to contain the parasite. Recognised via lesions observed by workers in king crab processing facilities in southern Chile, the parasite elicits giant cell formation in infected crabs. Merogony within haemocytes and fixed phagocytes proceeds apparent fusion of infected cells to produce multinucleate syncitia in which further development of the parasite occurs. Subsequent recruitment of adjacent cells within the haemal spaces of the hepatopancreas, the podocytes of the gill, and particularly in the subcuticular connective tissues, characterises the pathogenesis of A. rohanae. In late stages of infection, significant remodelling of the subcuticular tissues corresponds to the clinical lesions observed within processing plants. Sporogony of A. rohanae also occurs within the syncitial cytoplasm and culminates in production of bizarre spores, ornamented with distinctive tubular bristles. Spores occur in sets of 8 within a sporophorous vesicle. The description of A. rohanae offers considerable insight into the pathogenesis of giant-cell forming Microsporidia, signifies a new lineage of giant-cell forming Microsporidia in marine hosts, and may reflect emergence of a commercially-significant pathogen in the southern ocean Lithodes santolla fishery.

Laser-capture dissection and immunohistochemistry reveals chloride and mucous-cell specific gene expression in gills of seawater acclimated Atlantic salmon Salmo salar.

Laser-capture microdissection and immunohistochemistry were used to show that gene and protein expression varied in different cell types in the gills of Atlantic salmon Salmo salar, with chloride cells found to express high levels of sodium potassium ATPase and mucous cells expressing elevated levels of anterior gradient protein. It is therefore important that studies of gene expression in gill tissue take account of the proportion of the various cell types present.

Hyperpigmentation in North Sea dab Limanda limanda. II. Macroscopic and microscopic characteristics and pathogen screening.

An increasing trend in the prevalence of hyperpigmentation in the common dab Limanda limanda from the North Sea prompted us to investigate the potential role of infectious agents as causes or contributing factors to the condition. Dab representing 3 severity grades of hyperpigmentation were sampled for virology, bacteriology, histopathology and ultrastructure assessments. No cytopathic effect was recorded during virology testing, and bacteriological results showed no differences between normal and hyperpigmented dab. Histopathological assessment showed that the most significant changes occurred in the dermis as a result of chromatophore hyperplasia, namely melanophores and iridophores, alongside loose melanin granules. Dermal lymphocytic infiltration occasionally expanding into the epidermis and the underlying musculature was more frequent in highly pigmented dab than in normal fish, suggesting an active immune response. Ultrastructure studies showed additional disruption of the epithelial layer, with loose melanin granules between cells and a number of single or aggregated melanocytes. Dab representing different grades of hyperpigmentation kept in the laboratory alongside normal fish for a monitoring period of 18 mo showed no changes in their pigment distribution pattern, nor occurrence of new pigment in the normal fish. The current investigation found no association of hyperpigmentation in the common dab with infectious agents; therefore, understanding the cause of the condition remains a challenge which can now more reliably focus on a non-infectious origin hypothesis.

Differential characterization of emerging skin diseases of rainbow trout--a standardized approach to capturing disease characteristics and development of case definitions.

Farmed and wild salmonids are affected by a variety of skin conditions, some of which have significant economic and welfare implications. In many cases, the causes are not well understood, and one example is cold water strawberry disease of rainbow trout, also called red mark syndrome, which has been recorded in the UK since 2003. To date, there are no internationally agreed methods for describing these conditions, which has caused confusion for farmers and health professionals, who are often unclear as to whether they are dealing with a new or a previously described condition. This has resulted, inevitably, in delays to both accurate diagnosis and effective treatment regimes. Here, we provide a standardized methodology for the description of skin conditions of rainbow trout of uncertain aetiology. We demonstrate how the approach can be used to develop case definitions, using coldwater strawberry disease as an example.

Plastic parasites: extreme dimorphism creates a taxonomic conundrum in the phylum Microsporidia.

In this paper, we combine field observations of highly statistically significant co-occurrence with histopathological, ultrastructural and molecular phylogenetic analyses, to provide evidence for extreme morphological plasticity in a microsporidium parasite infecting the musculature of marine crabs. The parasite appears to alternate between lineages that culminate in production of either bizarre needle-like spores in the peripheral sarcoplasm of heart and skeletal muscle fibres (reminiscent of Nadelspora canceri infecting Cancer magister) or alternatively, Ameson-like spores with pronounced surface projections, in the skeletal muscles (as for Ameson pulvis, previously described infecting Carcinus maenas). Both lineages occur in direct contact with the cytoplasm of host muscle cells and can exist simultaneously within the same cell. Pathological data appears to reveal a remarkable shift in morphology during pathogenic remodelling of host tissues. Sequence analysis of multiple clones derived from amplification of the ssrRNA gene from infected regions of the heart and skeletal muscles appear to confirm the genetic identity of the two lineages. Furthermore, derived ssrRNA gene sequences are more similar (>99%) to N. canceri than to the coparasite Ameson michaelis infecting Callinectes sapidus (93%). Although molecular phylogenetic data support transfer of A. pulvis into the genus Nadelspora, the expansion in the generic description required to include such widely divergent characteristics is so significant as to be unfeasible within the current taxonomic framework of the phylum Microsporidia. At present, it is preferable to propose that the parasite infecting C. maenas forms a clade with other morphologically diverse but phylogenetically and ecologically similar muscle-infecting microsporidians from marine crustacean hosts. Given the strong evidence for significant plasticity in morphology amongst members of the phylum Microsporidia, novel approaches to phylogeny, based predominantly upon the informed use of molecular sequence data, are now deemed a necessity.