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The rapid growth in the human population has led to an increased requirement for readily available food sources. The aquaculture industry is a fundamental source for maintaining food supplies; however, it is subjected to mounting pressures to meet supply demands. Thus, limiting factors that negatively impact the cultivation of farmed aquatic organisms is essential. Gill disease is an increasing area of concern, resulting in substantial losses in farmed fish. Several microbial pathogens are known to cause gill disease and, in many instances, multiple pathogens or factors can be involved in the disease, resulting in complex gill disease (CGD). The role of mixed infections in gill disease is largely unknown, as such this review aims to examine data on previous infections and highlight the variety of microbes that might be involved in gill disease. The influence of climate change in the context of CGD is also discussed given the strong links between physicochemical extremes and numerous microbial gill pathogens. Understanding these factors will allow for improved diagnostic and therapeutic strategies to be implemented. [ABSTRACT FROM AUTHOR]

Abstract An in vitro model to study the host response to Neoparamoeba perurans , the causative agent of amoebic gill disease (AGD), was evaluated. The rainbow trout gill derived cell line, RTgill-W1, was seeded onto permeable cell culture supports and maintained asymmetrically with apical seawater. Cells were inoculated with either a passage attenuated or a recent wild clone of N. perurans. Amoebae, loaded with phagocytosed fluorescent beads, were observed associated with host cells within 20 min post inoculation (pi). By 6 h small foci of cytopathic effect appeared and at 72 h cytolysis was observed, with total disruption of the cell monolayer at 96 h pi. Due to cell monolayer disruption, the platform could not support proliferation of amoebae, which showed a 3-log reduction in parasite 18S rRNA mRNA after 72 h (106 copies at 1 h to 103 at 72 h pi). SEM observations showed amoebae-like cells with either short pseudopodia and a malleiform shape, or, long pseudopodia embedded within the gill cells and erosion of the cell monolayer. To study the host immune response, inoculated gill cells were harvested from triplicate inserts at 0, 1, 3, 6, 24 and 48 h pi, and expression of 12 genes involved in the Atlantic salmon response to AGD was compared between infected and uninfected cells and between amoebic clones. Both clones induced similar host inmate immune responses, with the up-regulation of proinflammatory cytokine IL1β, complement C3 and cell receptor MHC-1. The Th2 pathway was up-regulated, with increased gene expression of the transcription factor GATA3, and Th2 cytokines IL10, IL6 and IL4/13A. PCNA and AG-2 were also up-regulated. The wild clone induced significantly higher up-regulation of IL1β, MHC-1, PCNA, lysozyme and IL10 than the attenuated clone for at least some exposure times, but AG-2 gene expression was higher in cells inoculated with the attenuated one. A principal component analysis showed that AG-2 and IL10 were key genes in the in vitro host response to N. perurans. This in vitro model has proved to be a promising tool to study host responses to amoebae and may therefore reduce the requirement for in vivo studies when evaluating alternative therapeutants to AGD control. Highlights • In vitro gill epithelia model enabled study of host response to Neoparamoeba perurans. • The association of the parasite to the monolayer was studied by SEM. • A protocol for live cell imaging of N. perurans is described. • Host cytokines related to Th2 and cell proliferative pathways were up-regulated. [ABSTRACT FROM AUTHOR]

Amoebic gill disease (AGD) is one of the most important parasitic diseases of farmed Atlantic salmon. It is a source of major economic loss to the industry and poses significant threats to animal welfare. Previous studies have shown that resistance against this disease has a moderate, heritable genetic component, although the genes and the genetic pathways that contribute to this process have yet to be elucidated. In this study, to identify the genetic mechanisms of AGD resistance, we first investigated the molecular signatures of AGD infection in Atlantic salmon through a challenge model, where we compared the transcriptome profiles of the naïve and infected animals. We then conducted a genome-wide association analysis with 1,333 challenged tested fish to map the AGD resistance genomic regions, supported by the results from the transcriptomic data. Further, we investigated the potential of incorporating gene expression analysis results in genomic prediction to improve prediction accuracy. Our data suggest thousands of genes have modified their expression following infection, with a significant increase in the transcription of genes with functional properties in cell adhesion and a sharp decline in the abundance of various components of the immune system genes. From the genome-wide association analysis, QTL regions on chromosomes ssa04, ssa09, and ssa13 were detected to be linked with AGD resistance. In particular, we found that QTL region on ssa04 harbors members of the cadherin gene family. These genes play a critical role in target recognition and cell adhesion. The QTL region on ssa09 also is associated with another member of the cadherin gene family, protocadherin Fat 4. The associated genetic markers on ssa13 span a large genomic region that includes interleukin-18-binding protein, a gene with function essential in inhibiting the proinflammatory effect of cytokine IL18. Incorporating gene expression information through a weighted genomic relationship matrix approach decreased genomic prediction accuracy and increased bias of prediction. Together, these findings help to improve our breeding programs and animal welfare against AGD and advance our knowledge of the genetic basis of host-pathogen interactions. [ABSTRACT FROM AUTHOR]

Abstract Neoparamoeba perurans is the aetiological agent of amoebic gill disease (AGD) in salmonids, however multiple other amoeba species colonise the gills and their role in AGD is unknown. Taxonomic assessments of these accompanying amoebae on AGD-affected salmon have previously been based on gross morphology alone. The aim of the present study was to document the diversity of amoebae colonising the gills of AGD-affected farmed Atlantic salmon using a combination of morphological and sequence-based taxonomic methods. Amoebae were characterised morphologically via light microscopy and transmission electron microscopy, and by phylogenetic analyses based on the 18S rRNA gene and cytochrome oxidase subunit I (COI) gene. In addition to N. perurans , 11 other amoebozoans were isolated from the gills, and were classified within the genera Neoparamoeba , Paramoeba , Vexillifera , Pseudoparamoeba , Vannella and Nolandella. In some cases, such as Paramoeba eilhardi , this is the first time this species has been isolated from the gills of teleost fish. Furthermore, sequencing of both the 18S rRNA and COI gene revealed significant genetic variation within genera. We highlight that there is a far greater diversity of amoebae colonising AGD-affected gills than previously established. [ABSTRACT FROM AUTHOR]

Summary Gill disorders have become a significant problem during the marine phase of farming Atlantic salmon (Salmo salar L.). The term complex gill disease (CGD) includes a wide range of clinical gill disease presentations generally occurring from the end of summer to early winter on marine Atlantic salmon farms. The gross and histological lesions observed are the resultant culmination of exposure to a mixture of environmental insults, pathogenic organisms and farm management practices. None of the three principal agents purportedly associated with CGD (Desmozoon lepeophtherii , salmon gill poxvirus or Candidatus Branchiomonas cysticola) have been cultured successfully in-vitro, so individual in-vivo challenge studies to identify their pathogenesis have not been possible. Studies of cohabitation of single pathogen-infected fish with naïve fish, and epidemiological investigations are required urgently to elucidate the roles of these pathogens and other factors in CGD. [ABSTRACT FROM AUTHOR]

Abstract: Amoebic gill disease (AGD) is a pathogenic disease in salmonids caused by Neoparamoeba perurans. Treatment of AGD infection has been through freshwater bathing of the fish. However, as the availability of fresh water is often limited, hydrogen peroxide has been introduced as an alternative treatment. This study investigated the effect of hydrogen peroxide as treatment for AGD‐infected salmon (Salmo salar L.,) at different seawater temperatures and hydrogen peroxide dosages. In total, 600 fish were challenged with N. perurans and the severity of the AGD infection was measured using a gill score scale. After challenge and disease development, the fish were distributed into 12 tanks. The treatment was performed at different seawater temperatures (8°C, 12°C, 17°C) using different hydrogen peroxide doses. Each temperature included an untreated control group. Linear models were used to analyse gill score. A significant effect of treatment was found (−0.68 ± 0.05) regardless of dose and temperature, suggesting that hydrogen peroxide was effective in treating AGD. When the model included dose, a negative linear relationship between dose and gill score was found. The study proved that treatment of AGD with hydrogen peroxide was successful, as gills partially recovered following treatment and further disease development was delayed. [ABSTRACT FROM AUTHOR]

Eighteen orange pigment bacterial strains have been recovered from the gill of naturally diseased golden mahseer ( n = 9), Tor putitora (Hamilton, 1822) in Uttarakhand, India. Isolated strains were characterized by morphological and biochemical characteristics and 16S rRNA gene sequence, and were found to belong to the homogenous group. All the bacterial isolates were Gram-negative, flexirubin positive, catalase and cytochrome-oxidase positive, gliding, short (~ 1.9–2.7 μm in length) and straight rods. The 16S rRNA gene sequence analysis allocated the bacterium to taxa Chryseobacterium scophthalmum (GenBank accession nos. KM822770 , type strain C. scophthalmum TPBLGL 18), with C. scophthalmum strain LMG 13028 T as its closest relative, with 99% sequence similarity. Antibiotic susceptibility tests indicated that all the isolates were susceptible to oxytetracycline (2 μg), erythromycin (10 μg) and sulphadiazine-trimethoprim (100 μg). Histopathological study of the gill of naturally diseased golden mahseer revealed extensive epithelial cell hyperplasia, necrosis, fusion of secondary gill lamellae, degeneration of chloride cells and edema. Inflammation and degenerative changes were also observed in liver, heart, spleen, gall bladder and kidney of naturally diseased fish. The pathogenicity of C. scophthalmum TPBLGL 18 (representative strain) to golden mahseer was confirmed by intraperitoneal (i.p.) injection (0.1 mL volume) with 1.9 × 10 6 CFU/mL of bacterium, which resulted in appearance of gill lesions. Gill lesions in 75% of the challenged fish were reproduced 24 h post-injection (p.i.), and pure colony of C. scophthalmum were re-isolated from the gill, liver and kidney tissue of experimentally challenged golden mahseer. Histopathological studies of gill tissues of i.p injected golden mahseer revealed, clubbing, hyperplasia, hypertrophy, congestion and fusion of secondary gill lamellae. Therefore, in conclusion, our study demonstrates the virulence of C. scophthalmum in golden mahseer as the causative agent of bacterial gill disease (BGD). [ABSTRACT FROM AUTHOR]

The article discusses oxidative stress' association with amoebic gill disease (AGD) in Atlantic salmon Salmo salar. Topics include the diseases caused by Neoparamoeba perurans, bath treatment conducted against AGD, and monitoring and confirmation of AGD through gross gill scoring. Also included are details on enzymes and antioxidant metabolites' role in controlling the fish cells, protection of fish cells from oxidative damage, and oxidative stress' impact on health management practices.

Abstract: There have been recent efforts amongst immunologists to develop approaches for following individual fish during challenges with viral and bacterial pathogens. This study contributes to assessing the feasibility of using such approaches to study amoebic gill disease (AGD). Neoparamoeba perurans, agent of AGD, has been responsible for widespread economic and fish loss in salmonid aquaculture. With the emergence of AGD in Europe, research into infection dynamics and host response has increased. This study investigated the effect of repeat exposure to anaesthesia, a necessary requirement when following disease progression in individual fish, on N. perurans. In vitro cultures of N. perurans were exposed every 4 days over a 28‐day period to AQUI‐S® (isoeugenol), a popular anaesthetic choice for AGD challenges, at a concentration and duration required to sedate post‐smolt salmonids. Population growth was measured by sequential counts of amoeba over the period, while viability of non‐attached amoeba in the culture was assessed with a vital stain. AQUI‐S® was found to be a suitable choice for in vivo ectoparasitic challenges with N. perurans during which repetitive anaesthesia is required for analysis of disease progression. [ABSTRACT FROM AUTHOR]

The Indian major carp, Labeo rohita Hamilton, 1822 is a tropical freshwater cyprinid fish native to inland waters in Asia. Herein, we describe a novel myxozoan forming plasmodia in the gill lamellae of L. rohita from Ranjit Sagar Wetland in Punjab, India. Myxospores were consistent with the genus Myxobolus , round to elliptical in valvular view, lemon shaped in side view with a characteristic protrusion at the anterior end and a round posterior end; length 7.65 ± 0.07 μm, width 4.62 ± 0.09 μm. There were two polar capsules of equal length, pear shaped, length of polar capsule 2.54 ± 0.05 μm, width 1.60 ± 0.02 μm, with 5–6 turns of the polar filament. The 890 bp 18S rDNA sequence was up to 97% similar to M. catlae from other cyprinid fishes in India. In having, unique myxospore morphology and 18S rDNA sequence, we propose Myxobolus holzerae as new to science. [ABSTRACT FROM AUTHOR]

Elucidation of the role of infectious agents putatively involved in gill disease is commonly hampered by the lack of culture systems for these organisms. In this study, a farmed population of Atlantic salmon pre-smolts, displaying proliferative gill disease with associated Candidatus Branchiomonas cysticola, Ca. Piscichlamydia salmonis and Atlantic salmon gill pox virus ( SGPV) infections, was identified. A subpopulation of the diseased fish was used as a source of waterborne infection towards a population of naïve Atlantic salmon pre-smolts. Ca. B. cysticola infection became established in exposed naïve fish at high prevalence within the first month of exposure and the bacterial load increased over the study period. Ca. P. salmonis and SGPV infections were identified only at low prevalence in exposed fish during the trial. Although clinically healthy, at termination of the trial the exposed, naïve fish displayed histologically visible pathological changes typified by epithelial hyperplasia and subepithelial inflammation with associated bacterial inclusions, confirmed by fluorescent in situ hybridization to contain Ca. B. cysticola. The results strongly suggest that Ca. B. cysticola infections transmit directly from fish to fish and that the bacterium is directly associated with the pathological changes observed in the exposed, previously naïve fish. [ABSTRACT FROM AUTHOR]

Background: In September 2008, a disease outbreak characterized by acute, severe gill pathology and peritonitis, involving the gastrointestinal tract, was observed in an Atlantic salmon (Salmo salar L.) farm in north-western Norway. During subsequent sampling in November 2008 and January 2009, chronic proliferative gill inflammation and peritonitis was observed. Cumulative mortalities of 5.6-12.8% and severe growth retardation were observed. Routine diagnostic analysis revealed no diseases known to salmon at the time, but microsporidian infection of tissues was observed. Methods: To characterize the disease outbreak, a combination of histopathology, in situ hybridization (ISH), chitin, calcofluor-white (CFW) staining, and real-time PCR were used to describe the disease progression with visualization of the D. lepeophtherii stages in situ. Results: The presence of the microsporidian Desmozoon lepeophtherii was confirmed with real-time PCR, DNA sequencing and ISH, and the parasite was detected in association with acute lesions in the gills and peritoneum. ISH using a probe specific to small subunit 16S rRNA gene provided an effective tool for demonstrating the distribution of D. lepeophtherii in the tissue. Infection in the peritoneum seemed localized in and around pre-existing vaccine granulomas, and in the gastrointestinal walls. In the heart, kidney and spleen, the infection was most often associated with mononuclear leucocytes and macrophages, including melanomacrophages. Desmozoon lepeophtherii exospores were found in the nuclei of the gastrointestinal epithelium for the first time, suggesting a role of the gastrointestinal tract in the spread of spores to the environment. Conclusions: This study describes the progression of D. lepeophtherii disease outbreak in an Atlantic salmon farm without any other known diseases present. Using different methods to examine the disease outbreak, new insight into the pathology of D. lepeophtherii was obtained. The parasite was localized in situ in association with severe tissue damage and inflammation in the gills, peritoneal cavity and in the gastrointestinal (GI) tract that links the parasite directly to the observed pathology. [ABSTRACT FROM AUTHOR]

Amoebic gill disease ( AGD) caused by the amoeba Paramoeba perurans is an increasing problem in Atlantic salmon aquaculture. In the present PCR survey, the focus was to identify reservoir species or environmental samples where P. perurans could be present throughout the year, regardless of the infection status in farmed Atlantic salmon. A total of 1200 samples were collected at or in the proximity to farming sites with AGD, or with history of AGD, and analysed for the presence of P. perurans. No results supported biofouling organisms, salmon lice, biofilm or sediment to maintain P. perurans. However, during clinical AGD in Atlantic salmon, the amoeba were detected in several samples, including water, biofilm, plankton, several filter feeders and wild fish. It is likely that some of these samples were positive as a result of the continuous exposure through water. Positive wild fish may contribute to the spread of P. perurans. Cleaner fish tested positive for P. perurans when salmon tested negative, indicating that they may withhold the amoeba longer than salmon. The results demonstrate the high infection pressure produced from an AGD-afflicted Atlantic salmon population and thus the importance of early intervention to reduce infection pressure and horizontal spread of P. perurans within farms. [ABSTRACT FROM AUTHOR]

Increased disease tolerance is an important trait commonly incorporated into shrimp breeding programs. Sib-selection using experimental pathogen challenge tests are used to measure family based tolerance. It is critical for challenge tests to be standardised and repeatable for accurate genetic estimation. Accordingly, this study focused on establishing a method for uniformly challenging Black Tiger shrimp ( Penaeus monodon ) to an acute gill-associated virus (GAV) infection. A stock inoculum of GAV (10 5.27 GAV RNA copies μL − 1 inoculum) was prepared from infected shrimp and used as the source of infection for the challenge methodologies investigated. Three challenge approaches compared in groups of juvenile P. monodon (2–10 g) were; intramuscular injection, ingestion of fresh or frozen diced muscle tissue from GAV-infected shrimp and immersion in water containing the GAV inoculum. Intramuscular injection using a weight-standardised dose of the inoculum resulted in cumulative mortality surpassing 50% on Day 7 post-challenge. Immersion of shrimp for 2 h in water comprising a 1:1000 dilution of the inoculum resulted in no mortalities over the 11 day trial period. GAV RT-qPCR analysis also identified no evidence of any shrimp becoming infected by the immersion method. Feeding shrimp either fresh or frozen diced muscle tissue of moribund shrimp with an acute GAV infection generated cumulative mortality that reached/surpassed 50% on day 11 post-challenge. Compared to the survivors of the injection group (mean = 10 7.73 ± 0.49 GAV RNA copies/μg total RNA), RT-qPCR analysis identified GAV infection loads to be less uniform and 100- to 1000-fold lower among survivors of feeding either fresh or frozen muscle tissue (mean = 10 5.71 ± 1.97 or 10 4.77 ± 1.90 GAV RNA copies/μg total RNA, respectively). Coefficient of variation (CV) values for the GAV infection load data supported survivors of injection (CV = 0.06) having a more uniform infection load compared to the survivors of either fresh (CV = 0.41) or frozen (CV = 0.33) tissue ingestion. Of the three challenge approaches assessed for their suitability in measuring GAV tolerance, injection was clearly identified to provide the most uniform and reliable means of infecting shrimp with a defined dose of GAV and therefore is the preferred method of infection to use for GAV challenge tests. [ABSTRACT FROM AUTHOR]

Amoebic gill disease ( AGD) in farmed Atlantic salmon is caused by the amoeba Paramoeba perurans. The recent establishment of in vitro culture techniques for P. perurans has provided a valuable tool for studying the parasite in detail. In this study, flow cytometry was used to generate clonal cultures from single-sorted amoeba, and these were used to successfully establish AGD in experimental Atlantic salmon. The clonal cultures displayed differences in virulence, based on gill scores. The P. perurans load on gills, determined by qPCR analysis, showed a positive relationship with gill score, and with clonal virulence, indicating that the ability of amoebae to proliferate and/or remain attached on gills may play a role in virulence. Gill scores based on gross signs and histopathological analysis were in agreement. No association between level of gill score and specific gill arch was observed. It was found that for fish with lower gill scores based on histopathological examination, gross examination and qPCR analysis of gills from the same fish were less successful in detecting lesions and amoebae, respectively. [ABSTRACT FROM AUTHOR]

Amoebic gill disease (AGD) has been an economically significant problem for the Tasmanian Atlantic salmon Salmo salar aquaculture industry for over 25 years. More recently, AGD has emerged as a major issue in other growing regions. Freshwater bathing remains the most effective treatment, although progress with selective breeding has shown that there are genetic mechanisms for resistance to be exploited. In this study, we compared the AGD resistance of Atlantic salmon, brown trout ( Salmo trutta ), and their interspecies hybrid. Using 22 Atlantic salmon and 20 brown trout broodstock in a factorial mating design, populations of Atlantic salmon, brown trout, and each reciprocal hybrid were produced. All populations were transferred to sea cages at 15 months of age and subjected to natural, chronic AGD challenge under semi-commercial conditions for six months. Disease severity was monitored over four infection cycles and AGD resistance calculated using gill scoring, a previously reported, industry-standard measure of gross AGD pathology. While the Atlantic salmon population became infected and required freshwater bathing four times during the trial, both hybrids and brown trout became infected and required bathing only once. Heterosis for AGD resistance was significant, with hybrids displaying up to a 69% improvement over the mid-parent average and a 48% improvement over the best parent. The brown trout ♀ × Atlantic salmon ♂ (TS) population exhibited the highest levels of AGD resistance throughout the study, which covered the rearing of animals up until 21 months of age. Over this period the TS hybrid performed comparably to Atlantic salmon for growth rate and survival. The Atlantic salmon × brown trout hybrid represents a model for further exploitation to advance the understanding of AGD resistance in salmonids, and may provide options for commercial growers. Statement of relevance We present a hybrid salmonid model to advance AGD management. [ABSTRACT FROM AUTHOR]

Amoebic gill disease (AGD) and sea lice are two of the most significant disease issues that the Norwegian Atlantic salmon aquaculture industry is facing. Although both diseases respond to various extents, to freshwater treatment, the chemistry, interactions, and efficacy of treatment can be variable. These variations can have significant impacts upon the success and failure of treatment and costs to the production cycle. Although it is known that soft freshwater is most effective in bathing of Atlantic salmon with AGD and that most of the freshwaters in Norway fall into the soft category, the low alkalinity and buffering capacity of such waters may impact on the pH and metal toxicity of the water source in use. Similarly dissolved organic carbon can be beneficial in treatment, although sequestration of metal ions can be reversed as the water pH drops due to high densities of fish and accumulations of carbon dioxide. Alternative treatments such as the use of oxidative disinfectants such as hydrogen peroxide used for AGD and sea lice control may have potential although the interactions in seawater with organic loads and dissolved organic carbon are unclear. Similarly the use of oxidative disinfectants in freshwater will depend upon the water chemistry and interactions with treatment chemicals, fish, and water organic content. The logistics of treating large biomasses of Atlantic salmon on marine farms are challenging. The use of well boats offers potential although maintaining water quality during treatments is essential for both AGD and sea lice treatments to optimize fish welfare and treatment efficacy. [ABSTRACT FROM AUTHOR]

A previously undescribed species of Entobdella is reported from the skin of the Greenland halibut, Reinhardtius hippoglossoides (Pleuronectiformes, Pleuronectidae). Entobdella whittingtoni sp. nov. differs from other species of Entobdella, including skin parasites of the related pleuronectids Hippoglossus hippoglossus (Atlantic halibut) and H. stenolepis (Pacific halibut), in lacking papillae on the ventral surface of the haptor. Other characteristics of E. whittingtoni are as follows: the absence of vitelline follicles lateral to the pharynx thereby exposing gut caeca in this region of whole mounts; the presence of a circular feature of unknown function, resembling a rosette in sections, attached to the wall of the internal male accessory reservoir; the lack of eyes. Papillae are also absent from the ventral surface of the haptor of the gill-parasitic entobdelline Branchobdella pugetensis, a gill parasite of the pleuronectid Atheresthes stomias. This raises the question as to whether this gill parasite has evolved from a skin-parasitic ancestor similar to E. whittingtoni. An answer to this question requires a more detailed study of the male reproductive apparatus of B. pugetensis and the use of molecular techniques to explore the relationship between B. pugetensis and E. whittingtoni [ABSTRACT FROM AUTHOR]

The article focuses on the effect of bacterial gill disease in cultured fish like the rainbow trout Oncorhynchus mykiss in six replicated water recirculation aquaculture systems. Based on results, it states that bacterial contamination had occurred during sample processing, resulting in contamination with DNA from various lactic acid bacteria including Weisella, Lactobacillus, and Leuconostoc. A graph depicting the mean standard error abundance counts for bacteria is presented.

The interbranchial lymphoid tissue (ILT) was recently described in the gills of salmonids. This study examined changes in the ILT during a parasitic infection in marine environment, using amoebic gill disease (AGD) as a model. Atlantic salmon (S almo salar ) experimentally infected with Neoparamoeba perurans were sampled at 0, 3, 7, 14 and 28 days post challenge. Transversal sections of three areas of the gills (dorsal, medial and ventral) were histologically assessed for morphological and cellular changes. AGD induced morphological changes and a cellular response in the ILT of affected fish. These changes included a significant increase in the ILT surface area in fish 28 days after AGD challenge, compared to control fish at the same time point. The length of the ILT increased significantly 28 days post exposure in the dorsal area of the gill arch in the fish affected by AGD. The lymphocyte density of the ILT increased after AGD challenge, peaking at 7 days post exposure; however, by 28 days post exposure, a reduction of lymphocyte density to values close to pre-infection levels was observed. PCNA immunostaining revealed that epithelial hyperplasia was the most likely factor contributing to the ILT enlargement in the affected fish. [ABSTRACT FROM AUTHOR]

Abstract: Chlamydial infections of fish are emerging as an important cause of disease in new and established aquaculture industries. To date, epitheliocystis, a skin and gill disease associated with infection by these obligate intracellular pathogens, has been described in over 90 fish species, including hosts from marine and fresh water environments. Aided by advances in molecular detection and typing, recent years have seen an explosion in the description of these epitheliocystis-related chlamydial pathogens of fish, significantly broadening our knowledge of the genetic diversity of the order Chlamydiales. Remarkably, in most cases, it seems that each new piscine host studied has revealed the presence of a phylogenetically unique and novel chlamydial pathogen, providing researchers with a fascinating opportunity to understand the origin, evolution and adaptation of their traditional terrestrial chlamydial relatives. Despite the advances in this area, much still needs to be learnt about the epidemiology of chlamydial infections in fish if these pathogens are to be controlled in farmed environments. The lack of in vitro methods for culturing of chlamydial pathogens of fish is a major hindrance to this field. This review provides an update on our current knowledge of the taxonomy and diversity of chlamydial pathogens of fish, discusses the impact of these infections on the health, and highlights further areas of research required to understand the biology and epidemiology of this important emerging group of fish pathogens of aquaculture species. [Copyright &y& Elsevier]

Abstract: Genetic selection is being developed as a management tool for the control of amoebic gill disease (AGD) in Atlantic salmon. AGD is caused by an external gill parasite and is an animal health issue that results in significant economic loss to the Tasmanian salmon industry. This paper presents genetic parameters for AGD resistance, describes patterns of genetic variation over multiple infection cycles, and discusses the development of a selective breeding program to exploit this variation. Measurements of visible gill signs were made on over 12,000 individuals representing 326 sires and 297 dams from four genetically linked year classes. Between three and six sequential infections were measured on each year class. All measures of gill signs in all year classes had significant genetic variation with heritabilities ranging from 0.09±0.03 to 0.56±0.07. Genetic correlations between infections indicate two distinct traits which are only weakly correlated (average rg =0.24). One is measured at first infection on naïve fish and the other can be measured at all subsequent infections. This pattern is suggestive of an adaptive immune response for reinfections, and conforms with patterns seen for resistance to other parasitic diseases in terrestrial livestock. In an analysis combining all year classes, the heritability for first infection was 0.14±0.02 and heritabilities for reinfections ranged from 0.23±0.08 to 0.40±0.03. Reinfections appeared to be mostly under common genetic control, although there appear to be additional genetic traits that cause lower correlations for a small proportion (about 10%) of the population. Consistent and stable patterns of inheritance are indicated by the medium to high genetic correlations between year classes and by the high genetic correlations between infection cycles with a seasonal shift. Estimation of genetic correlations between AGD resistance and growth rate are problematic due to confounding effects but it is likely that this correlation is near zero. Selection for AGD resistance can assist with disease management and is part of the breeding objective of the Tasmanian salmon breeding program. Adaptive AGD resistance is one of the primary selection traits and a field challenge based on assessment of gill signs is an effective way of selecting for resistance. The current selective breeding strategy is predicted to increase the interval between treatments by 3% per year. [Copyright &y& Elsevier]

Gill disease in salmonids is characterized by a multifactorial aetiology. Epitheliocystis of the gill lamellae caused by obligate intracellular bacteria of the order Chlamydiales is one known factor; however, their diversity has greatly complicated analyses to establish a causal relationship. In addition, tracing infections to a potential environmental source is currently impossible. In this study, we address these questions by investigating a wild brown trout ( Salmo trutta) population from seven different sites within a Swiss river system. One age class of fish was followed over 18 months. Epitheliocystis occurred in a site-specific pattern, associated with peak water temperatures during summer months. No evidence of a persistent infection was found within the brown trout population, implying an as yet unknown environmental source. For the first time, we detected ' Candidatus Piscichlamydia salmonis' and ' Candidatus Clavochlamydia salmonicola' infections in the same salmonid population, including dual infections within the same fish. These organisms are strongly implicated in gill disease of caged Atlantic salmon in Norway and Ireland. The absence of aquaculture production within this river system and the distance from the sea, suggests a freshwater origin for both these bacteria and offers new possibilities to explore their ecology free from aquaculture influences. [ABSTRACT FROM AUTHOR]

Chloramine-T (CLT) is a candidate for approval for use in U.S. aquaculture to control mortality in freshwater-reared salmonids caused by bacterial gill disease (causative agent, Flavobacterium branchiophilum). The proposed treatment regimen is to administer CLT at 12-20 mg/L in a static or flow-through bath for 60 min/d on three alternate or consecutive days. To estimate a CLT margin of safety, defined as the highest dosing regimen above the proposed maximum therapeutic regimen at which no adverse effects are observed, we conducted seven experiments with fry, fingerling, and juvenile rainbow trout Oncorhynchus mykiss that examined mortality and an eighth experiment that examined mortality, gross pathology, and histopathology after CLT exposure. In each experiment, triplicate groups of fish were exposed to a range of CLT concentrations representing 0, 1, 1.5, 2, 2.5, 3, 3.5, 4, or 5× the highest proposed dose (20 mg/L) for 3× the proposed treatment duration (60 min) on three alternate or consecutive days at 8°C or 14°C. The survival of fry and fingerlings was unaffected by exposure to CLT concentrations as high as 100 and 60 mg/L, respectively (survival = 97.3-100%). Although the survival of juvenile fish was unaffected by exposure to 20 mg/L, exposure to higher CLT concentrations significantly reduced survival (≤10.0% at 100 mg/L). Across experiments, 92% of all mortalities occurred within 20 h of the first exposure to CLT. The histopathological changes of most concern were associated with gill tissues, but these were evident only in moribund fish exposed to doses of 60 mg/L or higher. Based on analysis of the survival data, the margin-of-safety estimates were approximately 100 mg/L for rainbow trout fry, at least 60 mg/L for fingerlings, and 50-60 mg/L for juveniles. Tissue responses to CLT at these concentrations were minor and did not warrant decreasing these estimates. [ABSTRACT FROM AUTHOR]

Infectious gill diseases of marine salmonid fish present a significant challenge in salmon-farming regions. Infectious syndromes or disease conditions affecting marine-farmed salmonids include amoebic gill disease (AGD), proliferative gill inflammation (PGI) and tenacibaculosis. Pathogens involved include parasites, such as Neoparamoeba perurans, bacteria, such as Piscichlamydia salmonis and Tenacibaculum maritimum, and viruses, such as the Atlantic salmon paramyxovirus (ASPV). The present level of understanding of these is reviewed with regard to risk factors, potential impacting factors, methods of best practice to mitigate infectious gill disease, as well as knowledge gaps and avenues for future research. [ABSTRACT FROM AUTHOR]

Proliferative gill disease (PGD) in channel catfish Ictalurus punctatus is caused by the myxozoan parasite Henneguya ictaluri, which uses the freshwater oligochaete Dero digitata as an alternate host. Controlled studies on the transmission of PGD require sustainable D. digitata mass cultures. We developed methods to grow and sustain large D. digitata populations and compared population growth in aerated versus nonaerated containers. White paper towels (2-3-cm squares) were placed into six 10.7-L dish pans into which 4 L of autoclaved pond water from commercial channel catfish ponds were then added along with 0.1 g of fish food. Each of the six dish pans was initially stocked with 100 D. digitata and maintained at 22-25°C; three pans received aeration, and three did not. All worms were counted and returned to their respective pans once each week for 5 weeks. To compensate for evaporative loss, autoclaved pond water was added to the pans weekly, and pond water and paper towels were completely changed after 4 weeks. Over 5 weeks, the mean number of worms per pan increased significantly more in the nonaerated pans than in the aerated pans. We have maintained D. digitata mass cultures in our laboratory for over a year, starting with two pans containing 100 worms each. Through routine exchanges of pond water and paper towel squares, these populations have expanded to 16 pans, each supporting 3,000-6,000 worms. We have also removed thousands of worms periodically to give to other researchers or for research in our laboratory. Using methods described here, researchers can maintain D. digitata mass cultures and predict population numbers that will be available at given times for studies on myxozoan life cycles and oligochaete control. [ABSTRACT FROM AUTHOR]

Abstract: Early-rearing salmonids in Ontario, Canada government fish hatcheries have been persistently affected by bacterial gill disease (BGD), and outbreaks at these locations have often been associated with high morbidity and mortality. The causative agent of BGD, Flavobacterium branchiophilum, is ubiquitous in fresh water, and outbreaks of BGD are considered to be associated with deleterious environmental conditions. This paper summarizes a 14-month rearing unit-level prospective nested matched case–control investigation at six Ontario government hatcheries (raising a total of six different salmonid species) to identify, and quantify the effects of, important predictors of BGD outbreaks. Ongoing husbandry data were collected on all early-rearing (<9 months of age) fish tank-lots (“tank-lot”=a group of fish from a specific lot existing in a single hatchery tank for a given period during the study time frame) at participating hatcheries, and all outbreaks of BGD were confirmed by light microscopy during the study period. Control tank-lots were selected at the end of the study and matched to individual cases based on time, hatchery, and species. Data were analyzed using logistic regression modeling, controlling for fish age. The final multivariable model indicated that affected tank-lots were significantly more likely to have had lower fish numbers, lower individual fish weights, higher mortality levels and higher feeding rates during the week preceding observed BGD outbreaks than were asymptomatic control tank-lots. Refinements in the observation and manipulation of these factors could therefore aid in the prevention of fish losses associated with observable BGD outbreaks. The predictive (as opposed to causal) nature of the identified factors needs to be considered, and further research is required to understand the relationships between these factors and BGD. [Copyright &y& Elsevier]

The article reports on the investigation related to the amoebic gill disease that affected the hatchery-reared ayu fish, in Japan. As reported the mortality which was first noticed in early April 2008 had increased by April 20, 2008. During the investigation the gills were dissected from one of the dead fish and then a single gill was processed for routine histology. The results showed that gill pathology in the ayu was caused by N. perurans Oligonucleotide primers.

In recent years, large losses of migrating adult sockeye salmon (Oncorhynchus nerka) from the Fraser River, British Columbia, Canada, have resulted in reductions in catches and productivity. We investigated patterns of mortality and the occurrence of the myxosporean parasite Parvicapsula minibicornis in adult sockeye salmon from Cultus Lake, tributary to the Fraser River. Using data from a captive broodstock program, we found that early migrants to Cultus Lake had less severe P. minibicornis infections and were more likely to survive to maturity than those fish that arrived later after they had presumably held in the warmer Fraser River. We found P. minibicornis in kidneys and gills of spawners. In some fish, significant histopathology in the gills that included severe inflammation and hyperplasia of the gill lamellae was observed; the severity of the disease was correlated with the severity of P. minibicornis infections. Kidney and gill pathologies were more prevalent and more severe in fish that died before spawning compared with those that matured successfully. Gill disease associated with P. minibicornis infections had not been previously identified in Fraser River sockeye salmon, and its role in the loss of spawners needs further investigation. Ces dernières années, de lourdes pertes de saumons rouges (Oncorhynchus nerka) adultes migrateurs dans le fleuve Fraser, Colombie-Britannique, Canada, ont causé des réductions des prises et de la productivité. Nous examinons les patrons de mortalité et l’occurrence de la myxosporidie parasite Parvicapsula minibicornis chez les saumons rouges adultes du lac Cultus qui se déverse dans le fleuve Fraser. À l’aide de données provenant d’un programme impliquant un stock reproducteur captif, nous observons que les migrateurs précoces dans le lac Cultus ont des infections à P. minibicornis moins sévères et qu’ils sont plus susceptibles de survivre jusqu’à la maturité que les poissons qui arrivent plus tard après avoir vraisemblablement été retenus dans les eaux plus chaudes du fleuve Fraser. Nous avons trouvé P. minibicornis dans les reins et les branchies des reproducteurs. Nous avons observé chez certains poissons une importante histopathologie des branchies et, en particulier, une inflammation sévère et une hyperplasie des lamelles branchiales; la gravité de la maladie est en corrélation avec la sévérité des infections de P. minibicornis. Les pathologies des reins et des branchies sont plus fréquentes et plus graves chez les poissons qui sont morts avant la fraie, par comparaison à ceux qui ont frayé avec succès. On n’avait pas signalé auparavant la maladie des branchies associée à P. minibicornis chez les saumons rouges du fleuve Fraser et il faudra étudier plus au fond son rôle dans la perte des reproducteurs. [ABSTRACT FROM AUTHOR]

Amoebic gill disease (AGD) is a proliferative gill tissue response caused by Neoparamoeba perurans and is the main disease affecting Australian marine farmed Atlantic salmon. We have previously proposed that macroscopic gill health (‘gill score’) trajectories and challenge survival provide evidence of a change in the nature of resistance to AGD. In order to examine whether the apparent development of resistance was because of an adaptive response, serum was sequentially sampled from the same individuals over the first three rounds of natural AGD infection and from survivors of a subsequent non-intervention AGD survival challenge. The systemic immune reaction to ‘wildtype’ Neoparamoeba sp. was characterized by Western blot analysis and differentiated to putative carbohydrate or peptide epitopes by periodate oxidation reactions. The proportion of seropositive fish increased from 46% to 77% with each AGD round. Antibody response to carbohydrate epitope(s) was immunodominant, occurring in 43–64% of samples. Antibodies that bound peptide epitope were identified in 16% of the challenge survivors. A 1:50 (single-dilution) enzyme-linked immunosorbent assay confirmed a measurable immune titre in 13% of the survivors. There was no evidence that antibodies recognizing wildtype Neoparamoeba provided significant protection against AGD. [ABSTRACT FROM AUTHOR]

The article presents a research on the myxozoan parasite Henneguya ictaluri that caused the proliferative gill disease (PGD) in channel catfish Ictalarus punctatus. It notes that the extensive gill damage was caused by prolonged exposure of channel catfish to the actinospore stage of the parasite, resulting to reduced production and significant mortality in commercial operations. Findings showed that increases in parasite load correlated with percent mortality in sentinel fish, as did increases in mean actinospore concentrations. It is believed that both applications are more rapid than current protocols for assessing the PGD status of a catfish pond and identified actinospore levels that correlate to both high and low risk of fish loss.

Abstract: Early-rearing salmonids in Ontario Ministry of Natural Resources (OMNR) fish hatcheries have been consistently affected by bacterial gill disease (BGD) (causative agent: Flavobacterium branchiophilum) for many years. Separate retrospective epidemiological investigations of BGD treatments at two OMNR fish hatcheries (Hatcheries A and B) for the 1999 production year were conducted using on-site hatchery records. Both investigations were carried out at the rearing unit-level, with early-rearing (<9 months of age) “tank-lot” as the unit of analysis to identify unique fish populations over time. Multivariable repeated measures logistic regression models were created for both hatchery datasets, controlling for lot-level and species effects. For Hatchery A, the species brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) were significantly associated with BGD treatment, as well as lower water exchange rate, and higher feeding and mortality percentages during the 2 weeks previous to BGD treatment. At Hatchery B, the species brook trout (S. fontinalis) and splake (Salvelinus namaycush × S. fontinalis) were significantly associated with BGD treatment, as well as lower individual fish weights and treatment for BGD during the previous week. These results emphasize the importance of water quality, feeding rate, fish size and prior mortality on the development of BGD. Significant hatchery and species effects were evident, and future observational research on BGD must account for these factors in their design and analysis. [Copyright &y& Elsevier]

Abstract: Survival in an experimental disease challenge test or to natural disease challenge is utilised by aquaculture breeding programs as the selection trait for disease resistance. However, these trials are expensive and do not offer the ability to retest animals. The aim of this study was therefore to estimate genetic parameters for resistance to amoebic gill disease (AGD) measured by a categorical scale of gross gill signs (“gill score”) and survival in a field challenge in order to establish whether gill score provides adequate measurement of genetic variation for AGD resistance compared to an AGD challenge survival. A total of 1504 Atlantic salmon smolt, representing 140 full-sib families, was transferred to a marine site in SE Tasmania. The gills were assessed by gill score prior to freshwater bathing on the first two rounds of infection, and then the disease was allowed to develop until mortalities began. Gill score was reassessed after 50days and mortality was allowed to continue until it had reached a plateau at 100days. The overall survival rate was 32.3% but varied from 0% to 69% between families. Estimated narrow sense heritability for AGD resistance assessed by gill score varied between 0.23 and 0.48 over the three rounds of infection. Heritability of AGD survival challenge was 0.40 to 0.49 on the observed scale using binary and longitudinal measures. Gill score and survival showed a weak (−0.19) to strong (−0.96) negative genetic correlation which improved when assessed closer to the survival challenge. Estimated genetic gains by selection of the top one hundred estimated breeding values for gill score indicated that up to 82% of the expected gain in survival can be achieved when compared to estimated gain by selection upon survival (days to death), thus minimising selection costs and improving fish welfare whilst allowing repeat measures to be made. The results show that genetic variation of gill score at the early onset of losses closely compares with survival results if the disease is allowed to progress without subsequent freshwater bathing. Gill score may therefore be utilised as a nondestructive and repeatable selection trait for breeding Atlantic salmon with greater resistance to AGD. [Copyright &y& Elsevier]

Abstract: Proliferative gill inflammation, a respiratory disease of apparently multifactorial aetiology, affects seawater-farmed Atlantic salmon in Norway and may be associated with significant losses. In the present study, the gill-associated bacterial community in fish suffering PGI as diagnosed by histology was compared with that of clinically healthy fish by Reverse Transcriptase Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis. ‘Candidatus Piscichlamydia salmonis’, which forms histologically detectable intracellular inclusions commonly called epitheliocysts, was identified in 16 of 21 fish displaying PGI, normally as the dominant phylotype. Although identified by RT-DGGE in many clinically healthy fish from PGI affected farms, this bacterium was only detected in 7 of 48 fish from PGI-free farms, of which all positives interestingly originated from a single farm. Taken together, these results reveal a positive association between ‘Candidatus Piscichlamydia salmonis’ and PGI in the investigated material from 10 geographically distinct farms. Furthermore, a wide distribution of γ-proteobacteria was detected, but the bacterial communities of individual fish gills were generally quite simple and often dominated by one or two phylotypes, most commonly Burkholderia-like bacteria (previously Pseudomonads) and Psychrobacter spp. Representatives of spoilage or fish pathogenic genera e.g. Photobacterium, Flavobacterium, Aliivibrio, Shewanella and Tenacibaculum, were less frequently identified and apparently in low numbers. Sequences representing at least one undescribed species closely related to fish pathogenic Francisella spp. were also identified. [Copyright &y& Elsevier]

This study examined the efficacy of bithionol as a prophylactic or therapeutic oral treatment for Atlantic salmon (AS), Salmo salar, affected by amoebic gill disease (AGD). Furthermore, it explored the interaction of bithionol oral therapy with the current standard treatment (a freshwater bath for at least 3 h). The efficacy of three medicated feeds was determined in the trial by feeding AGD-affected AS at 1% body weight (BW) day−1 either oil coated commercial feed (control) or prophylactic and therapeutic bithionol at 25 mg kg−1 feed. Feeding commenced 2 weeks prior to exposure to Neoparamoeba spp. at 300 cells L−1 and continued for 49 days post-exposure (PE). Bithionol when fed as a 2-week prophylactic or therapeutic treatment at 25 mg kg−1 feed delayed the onset of AGD pathology and reduced the percentage of gill filaments with lesions. Administration of a 3-h freshwater bath at 28 days PE significantly reduced amoeba numbers to a similar level across all treatments; in contrast, gross gill score and percent lesioned filaments were reduced to different extents, the control having a significantly higher score than both bithionol treatments. Following the freshwater bath, clinical signs of AGD increased at a similar level across all treatments, albeit controls were significantly higher than the bithionol treatments immediately following freshwater treatment. This study demonstrated that bithionol at 25 mg kg−1 feed, when fed as a 2-week prophylactic or a therapeutic treatment, delayed and reduced the intensity of AGD pathology and warrants further investigation as a treatment for AGD-affected AS. [ABSTRACT FROM AUTHOR]

The article provides information about the presence of the three new monogenean species from Mormyrus rume in Ivory Coast. The presence of these monogenean species of the genus Bouixella Euzet & Dossou revealed through the gill parasited study conducted from the elephant fish found at the Ayamé manmade lake. These species are mainly differentiated from all other species of the genus based on the morphology and size of the sclerotised parts of haptor. Additional description about Bouixella (B.) gorei, B. yaoi and B. koutouani are also presented.

Abstract: Chloramine-T (Cl-T) has been used safely and effectively to control bacterial gill disease in salmonids at a maximum exposure regimen of up to four consecutive, once-daily exposures administered for 60 min at 20 mg/L. However, data to document safe treatment concentrations of Cl-T are lacking for freshwater-reared fish other than salmonids. We report the histopathology resultant from the administration of 12 consecutive, once-daily, 180-min static immersion baths of 0, 20, 50, or 80 mg Cl-T/L to walleye (20 °C) and channel catfish (27 °C). Twelve fish of each species were euthanized immediately before the first exposure (initial controls) and then after the twelfth exposure and 7 and 14 days after the twelfth exposure. Only initial controls and fish euthanized immediately after the twelfth exposure were processed for histological review because of the general lack of exposure-related lesions in exposed fish. The only exposure-related histological changes were in the spleen where significantly greater erythrocyte swelling and necrosis was observed in channel catfish exposed at 80 mg/L relative to exposure at 0 mg/L; similar histological changes were insignificant for walleye, though there appeared to be a shift in the general category of histological change with degenerative changes (necrosis, etc.) observed following exposure at 50 or 80 mg/L compared to the inflammatory and hemodynamic changes (congestion, leukocyte infiltrate, etc.) observed in walleye exposed at 0 or 20 mg/L. The only significant change in peripheral blood cytology was that walleye fingerlings exposed at 80 mg/L had significantly fewer mature red blood cells and significantly more immature red blood cells per oil-immersion field than controls. The histopathological changes observed following exposure to Cl-T under an exaggerated exposure regimen suggest that walleye or channel catfish therapeutically exposed to Cl-T will not have treatment-related histological changes. [Copyright &y& Elsevier]

Amoebic gill disease (AGD)-affected Atlantic salmon Salmo salar sometimes developed a serum-antibody response to wild-type Neoparamoeba spp. Five of 103 AGD-affected S. salar sampled possessed detectable antibodies that bound wild-type Neoparamoeba spp. western blotting revealed two distinctly different binding profiles. [ABSTRACT FROM AUTHOR]

Proliferative gill disease (PGD) is an emerging problem in Norwegian culture of Atlantic salmon ( Salmo salar). Parasites ( Ichthyobodo spp.) and bacteria ( Flexibacter/Flavobacterium) may cause PGD, but for most cases of PGD in farmed salmon in Norway, no specific pathogen has been identified as the causative agent. However, Neoparamoeba sp. and several bacteria and viruses have been associated with this disease. In the spring of 2006, a new poxvirus, salmon gill poxvirus (SGPV), was discovered on the gills of salmon suffering from PGD in fresh water in northern Norway. Later the same year, this virus was also found on gills of salmon at two marine sites in western Norway. All farms suffered high losses associated with the presence of this virus. In this study, we describe the entry and morphogenesis of the SGP virus in epithelial gill cells from Atlantic salmon. Intracellular mature virions (IMVs) are the only infective particles that seem to be produced. These are spread by cell lysis and by “budding” of virus packages, containing more that 100 IMVs, from the apical surface of infected cells. Entry of the IMVs appears to occur by attachment to microridges on the cell surface and fusion of the viral and cell membranes, delivering the cores into the cytoplasm. The morphogenesis starts with the emergence of crescents in viroplasm foci in perinuclear areas of infected cells. These crescents consist of two tightly apposed unit membranes (each 5 nm thick) that seem to be derived from membranes of the endoplasmic reticulum. The crescents develop into spheres, immature virions (IVs), that are 350 nm in diameter and surrounded by two unit membranes. The maturation of the IVs occurs by condensation of the core material and a change from spherical to boat-shaped particles, intracellular mature virions (IMVs), that are about 300 nm long. Hence, the IMVs from the SGP virus have a different morphology compared to other vertebrate poxviruses that are members of the subfamily Chordopoxvirinae, and they are more similar to members of subfamily Entomopoxvirinae, genus Alphaentomopoxvirus. However, it is premature to make a taxonomic assignment until the genome of the SGP virus has been sequenced, but morphogenesis clearly shows that this virus is a member of family Poxviridae. [ABSTRACT FROM AUTHOR]

Abstract: Several important cultured marine fish are highly susceptible to an ectoparasitic condition known as amoebic gill disease (AGD). In AGD-affected fish, modulation of IL-1β, p53 and p53-regulated transcripts is restricted to the (multi)focal AGD-associated gill lesions. To determine whether this lesion-restricted modulation of transcripts occurs on a transcriptome-wide scale and to identify mechanisms that underpin the susceptibility of fish to AGD, we compared the transcriptome of AGD lesions with “normal” tissue from AGD-affected and healthy individuals. Global gene expression profiling using a 16K salmonid microarray, revealed a total of 176 significantly regulated annotated features and of those, the modulation of 99 (56%) was lesion-restricted. Annotated transcripts were classified according to functional gene ontology. Within the immune response category, transcripts were almost universally down-regulated. In AGD-affected tissue, significant, coordinated down-regulation of the major histocompatibility complex class I (MHC I) pathway-related genes occurred during the later stages of infection and appeared to be mediated by down-regulation of interferon-regulatory factor (IRF)-1, independent of interferon-α, interferon-γ and IRF-2 expression. Within this micro-environment, suppression of the MHC I and possibly the MHC II pathways may inhibit the development of acquired immunity and could explain the unusually high susceptibility of Atlantic salmon to AGD. [Copyright &y& Elsevier]

Abstract: Chloramine-T is presently available in the USA to control mortalities associated with bacterial gill disease or external columnaris only through an Investigational New Animal Drug Permit authorized by the US Food and Drug Administration (FDA). Its US approval hinges on FDA''s acceptance of several key data, including those describing animal safety. Chloramine-T is presently applied in US aquaculture, by permit only, once daily on consecutive or alternate days for 1 h at 10 to 20 mg/L to control mortalities associated with bacterial gill disease or external columnaris. Our objective was to determine the safety of chloramine-T bath exposures at multiples of the proposed maximum treatment concentration (i.e., 0, 20, 60, 100, and 200 mg/L) administered on four consecutive days at 20 °C to lake sturgeon Acipenser fulvescens, northern pike Esox lucius, and walleye Sander vitreum, or at 27 °C to channel catfish Ictalurus punctatus, and largemouth bass Micropterus salmoides. All fish were tested as five to eight week old fry except for walleye and channel catfish which were tested as both fry and fingerling (fingerlings were at least four weeks older than the fry tested). Walleye and channel catfish were selected to evaluate the effects of life stage (fry vs. fingerling), temperature (walleye — 15, 20, or 25 °C; channel catfish — 22, 27, or 32 °C), exposure duration (60 vs. 180 min), and water chemistry (walleye only — reconstituted soft water vs. well water). Except for channel catfish fry, survival was significantly reduced only when fish were treated at 100 or 200 mg/L. Channel catfish fry survival was significantly reduced when exposed at 60 mg/L for 180 min at 27 °C. Based on our mortality data, chloramine-T administered once daily for 60 min on four consecutive days at concentrations of up to 20 mg/L is not likely to adversely affect survival of cool or warmwater fish cultured in freshwater. [Copyright &y& Elsevier]

Abstract: Bacterial gill disease (BGD) (causative agent: Flavobacterium branchiophilum) has been a persistent problem in early-rearing salmonids in the Ontario Ministry of Natural Resources (OMNR) fish hatchery system. Retrospective epidemiological investigations of BGD diagnoses and treatments in OMNR fish hatcheries during the period 1991–2001 were conducted using University of Guelph Fish Health Laboratory and OMNR central office data. All investigations were conducted at the lot-level, which is the major within-hatchery-level of population aggregation. Survivorship of BGD diagnosis in early-rearing lots within seven individual hatcheries ranged from 84.2 to 100%; within individual species groups, survivorship was lowest (84.6%) in brook trout (Salvelinus fontinalis) lots. Annual risk percentages (cumulative incidence) for BGD diagnosis within hatchery and species groups varied considerably among years. Multivariable proportional hazards survival analysis indicated that the species brook trout, and the Spring (March–May) season, were significantly associated with treatment for BGD. Combined, these results emphasize the importance of hatchery, species, and time on the development of BGD. Future observational research on this disease must consider these factors in their design and analysis. [Copyright &y& Elsevier]

Flavobacterium columnare is the causative agent of columnaris disease. The presence of lesions on the gills, skin and fins of diseased fish suggests that F. columnare is able to utilize fish skin mucus as a substrate for growth and that exposure to this material would alter the expression of genes involved in the colonization of the outer surfaces of the fish. Growth, biofilm formation, extracellular protease production and changes in protein expression of F. columnare strain C#2 cultured in media supplemented with juvenile Atlantic salmon skin mucus were compared with the same media without mucus. C#2 was able to grow by using mucus as the sole nutrient source. Growth in mucus-containing media induced cells to grow as a biofilm and extracellular protease activity increased in mucus-containing cultures. SDS-PAGE protein profiles showed that expression of six extracellular proteins increased in mucus-containing media. These results demonstrate that salmon surface mucus promotes the growth of F. columnare and that exposure to mucus alters the growth characteristics of this bacterium with regard to protease production and biofilm formation. Further characterization of mucus-induced physiological changes will increase our understanding of the basis of virulence of this economically important fish pathogen. [ABSTRACT FROM AUTHOR]

Bacterial gill disease (BGD), caused by Flavo-bacterium branchiophilum and other species of yellow-pigmented, filamentous bacteria, is a common and potentially catastrophic disease of hatchery (freshwater)-reared fish. Chloramine-T (Chl-T) is a biocide proven effective for controlling mortality in freshwater-reared fish diagnosed with BGD. However, Chl-T is not approved by the U.S. Food and Drug Administration for such use. To generate data in support of a U.S. approval, we evaluated the effectiveness of Chl-T (administered at 12 mg/L of static bath water for 60 min/d on three alternate days) to control mortality caused by BGD in freshwater-reared chum salmon Oncorhynchus keta, Apache trout O. gilae apache, and rainbow trout O. mykiss. For each species, the mean percent total mortality in Chl-T-treated tanks (N = 3) was significantly less than that in control tanks (N = 3): chum salmon = 8.9% versus 99.7%, Apache trout = 39.2% versus 97.9%, and rainbow trout = 5.7% versus 25.8%. Because the Chl-T treatment regimen was efficacious for each species, we conclude that our findings support the approval of Chl-T for use in the USA to control mortality in freshwater-reared salmon ids diagnosed with BGD. [ABSTRACT FROM AUTHOR]

Previous investigations into the pathophysiology of amoebic gill disease (AGD) have suggested that there are probable cardiovascular effects associated with this disease. In the present study Atlantic salmon, Salmo salar L., were experimentally infected by cohabitation with diseased individuals. Two commonly used vasodilators, sodium nitroprusside (SNP) and captopril, the angiotensin-converting enzyme (ACE) inhibitor, were used as tools to investigate possible vasoconstriction and/or renin–angiotensin system (RAS) dysfunction in AGD-affected animals. Within the SNP trial, results showed that AGD-affected fish exhibited lowered cardiac output ( Q), lowered cardiac stroke volume ( VS) and a significantly elevated systemic vascular resistance ( RS) compared with non-affected naïve counterparts. These effects were totally abolished following SNP administration (40 μg kg−1), however significant cardiovascular effects associated with SNP were not observed. Within the captopril trial, where AGD-affected fish were more diseased compared with the SNP trial, a significant hypertension was observed in AGD-affected fish. Captopril administration (10−4 mol L−1 at 1 mL kg−1) resulted in a significant drop in dorsal aortic pressure ( PDA) for both AGD-affected and naïve control fish. In terms of peak individual responses, captopril administration effectively lowered PDA in both AGD-affected and naïve control groups equally. The drop in PDA following SNP administration however was significantly greater in AGD-affected fish potentially suggesting disease-related vasoconstriction. The lack of significant cardiovascular effects directly associated with both SNP and captopril administrations possibly relate to the 6 h recovery period following surgical procedures. However, while variable, these results do suggest that there are significant cardiovascular effects including vasoconstriction and hypertension associated with AGD. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the present study was to examine the respiratory effects of chloramine-T, a proposed novel chemotherapeutic treatment for seawater-acclimated Atlantic salmon Salmo salar (L.) affected by amoebic gill disease (AGD). Following a surgical recovery period of 20–24 h, fish, both healthy (N =21) and AGD-affected (N =13) were exposed to either a 1-hour pulse of seawater containing chloramine-T at a therapeutic concentration of 10 mg L−1 (experimental), or 100 ml of sterile seawater (sham-treated controls). Arterial blood samples were repeatedly taken from a dorsal aortic catheter prior to exposure (0 h), immediately following exposure (1 h) and then at 3, 6, 12 and 24 h and various respiratory parameters measured. Results showed that there were no significant effects relating to chloramine-T exposure regardless of disease status. Additional examination of the pH-bicarbonate diagrams confirmed that there was minimal acid–base disturbance in fish exposed to chloramine-T regardless of disease status. Significant changes seen within the examined haematological parameters of both healthy and AGD-affected fish appeared to be related to the repeated withdrawal of blood for analysis of respiratory parameters. Overall these results suggest that the use of chloramine-T in full-strength seawater at the therapeutic concentration of 10 mg L−1 for 1 h had no significant respiratory effect in healthy or AGD-affected Atlantic salmon. Additionally, these results help to highlight the potential beneficial use of chloramine-T as a commercial treatment for gill diseased in marine Atlantic salmon. [Copyright &y& Elsevier]

Amoebic gill disease, the main disease of concern to the salmon industry in Tasmania, is caused by the amoeba, Neoparamoeba spp. Experimental infection can only be induced by exposure to wild-type (WT) parasites isolated from the gills of infected fish, as cultured amoebae are non-infective. To characterize the surface antigens of WT parasites, we produced monoclonal antibodies (mAbs) using subtractive immunization. Mice inoculated with non-infective parasites were treated with cyclophosphamide, to deplete reactive lymphocytes, and then immunized with different antigen preparations from infective parasites. When whole parasites were used for boosting, the percentage of WT unique mAbs was very high (86%) as was the percentage of mAbs specific for carbohydrate epitopes (89%). When deglycosylated membranes were used, the numbers of mAbs specific for non-carbohydrate epitopes did not increase, but the total number of WT unique mAbs was reduced (86–40%). Using an untreated membrane preparation, the total number of mAbs to surface molecules was very high, but all recognized carbohydrate epitopes. The total number of mAbs recognizing carbohydrate epitopes on the surface of the WT parasites was 97%, suggesting that the dominant epitopes on the surface molecules unique to WT parasites are carbohydrate in nature. [ABSTRACT FROM AUTHOR]

Abstract: This study examined the toxicity of bithionol to Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss in fresh- and seawater and the efficacy of bithionol as a 1h seawater bath treatment for amoebic gill disease (AGD). To examine toxicity, fish were bathed for 1, 3 and 6h in bithionol, an anti-protozoal at 0, 1, 5, 10, 25 and 35mgL−1 with toxicity determined by time to morbidity. Efficacy was examined by bathing AGD-affected Atlantic salmon and rainbow trout for 1h at bithionol concentrations of 1–25mgL−1. Efficacy was determined by examining gill amoeba counts and identifying percent lesioned gill filaments at 1 and 24h after bath exposure to bithionol. For both species, bithionol was determined to be toxic at 25 and 35mgL−1 exhibiting median lethal times (LT50s) ranging from 21 to 84min. Morbidity occurred in the 5 and 10mgL−1 treatments, however, due to sampling regime there were not enough fish available to calculate LT50s. Only bithionol at 1mgL−1 was considered non-toxic with no signs of morbidity. Bithionol was more toxic in seawater than freshwater and had no acute effects on gill Na+/K+ ATPase and succinic dehydrogenase, or plasma osmolality and chloride concentration. Bithionol at 1mgL−1 reduced percent lesioned gill filaments in Atlantic salmon and rainbow trout by 33 and 27%, respectively, compared to the seawater control. Similarly, numbers of amoeba were reduced by 33 and 43% for Atlantic salmon and rainbow trout, respectively, when compared to the seawater control. Furthermore, bithionol reduced percent lesioned gill filaments as much as did the current industry standard of freshwater. This study demonstrated that a 1h seawater bath containing 1mgL−1 bithionol could be an improvement to the current method of treatment for AGD-affected Atlantic salmon and rainbow trout. [Copyright &y& Elsevier]

The article discusses the histological investigations, viral ultrastructure and some genomic features of the freshwater Chinese mitten crab, Eriocheir sinensis Milne Edwards. Several reports of crab viral diseases during the 1970s and early 1980s are cited. The black gill syndrome (BGS) is cited as among the various diseases that appeared and severely affected crab production. Diseased Eriocheir sinensis exhibiting typical BGS collected from a farm in Hubei Province, China is examined.