Salmonids are affected by the economically significant whirling disease (WD) caused by the myxozoan parasite Myxobolus cerebralis. In the past, it was endemic to Eurasia, but it has now spread to different regions of North America, Europe, New Zealand, and South Africa. Among salmonids, rainbow trout is considered the most highly susceptible host. Upon entering to the host\'s body, the parasite invades the spine and cranium, resulting in whirling behaviour, a blackened tail, and destruction of cartilage. The disease is characterized by the infiltration of numerous inflammatory cells, primarily lymphocytes and macrophages, with the onset of fibrous tissue infiltration. Several efforts have been undertaken to investigate the role of various immune modulatory molecules and immune regulatory genes using advanced molecular methods including flow cytometry and transcriptional techniques. Investigation of the molecular and cellular responses, the role of STAT3 in Th17 cell differentiation, and the inhibitory actions of suppressors of cytokine signaling (SOCS) on interferons and interleukins, as well as the role of natural resistance-associated macrophage proteins (Nramp) in WD have significantly contributed to our understanding of the immune regulation mechanism in salmonids against M. cerebralis. This review thoroughly highlights previous research and discusses potential future directions for understanding the molecular immune response of salmonids and the possible development of prophylactic approaches against WD.

The increasing feasibility of assembling large genomic datasets for non-model species presents both opportunities and challenges for applied conservation and management. A popular theme in recent studies is the search for large-effect loci that explain substantial portions of phenotypic variance for a key trait(s). If such loci can be linked to adaptations, 2 important questions arise: 1) Should information from these loci be used to reconfigure conservation units (CUs), even if this conflicts with overall patterns of genetic differentiation? 2) How should this information be used in viability assessments of populations and larger CUs? In this review, we address these questions in the context of recent studies of Chinook salmon and steelhead (anadromous form of rainbow trout) that show strong associations between adult migration timing and specific alleles in one small genomic region. Based on the polygenic paradigm (most traits are controlled by many genes of small effect) and genetic data available at the time showing that early-migrating populations are most closely related to nearby late-migrating populations, adult migration differences in Pacific salmon and steelhead were considered to reflect diversity within CUs rather than separate CUs. Recent data, however, suggest that specific alleles are required for early migration, and that these alleles are lost in populations where conditions do not support early-migrating phenotypes. Contrasting determinations under the US Endangered Species Act and the State of California\'s equivalent legislation illustrate the complexities of incorporating genomics data into CU configuration decisions. Regardless how CUs are defined, viability assessments should consider that 1) early-migrating phenotypes experience disproportionate risks across large geographic areas, so it becomes important to identify early-migrating populations that can serve as reliable sources for these valuable genetic resources; and 2) genetic architecture, especially the existence of large-effect loci, can affect evolutionary potential and adaptability.

Evaluating studies over the past almost 40 years, this review outlines the current knowledge and research gaps in the use of isolated leucocytes in salmonid immunology understanding. This contribution focuses on the techniques used to isolate salmonid immune cells and popular immunological assays. The paper also analyses the use of leucocytes to demonstrate immunomodulation following dietary manipulation, exposure to physical and chemical stressors, effects of pathogens and parasites, vaccine design and application strategies assessment. We also present findings on development of fish immune cell lines and their potential uses in aquaculture immunology. The review recovered 114 studies, where discontinuous density gradient centrifugation (DDGC) with Percoll density gradient was the most popular leucocyte isolation method. Fish head kidney (HK) and peripheral blood (PB) were the main sources of leucocytes, from rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). Phagocytosis and respiratory burst were the most popular immunological assays. Studies used isolated leucocytes to demonstrate that dietary manipulations enhance fish immunity, while chemical and physical stressors suppress immunity. In addition, parasites, and microbial pathogens depress fish innate immunity and induce pro-inflammatory cytokine gene transcripts production, while vaccines enhance immunity. This review found 10 developed salmonid cell lines, mainly from S. salar and O. mykiss HK tissue, which require fish euthanisation to isolate. In the face of high costs involved with density gradient reagents, the application of hypotonic lysis in conjunction with mico-volume blood methods can potentially reduce research costs, time, and using nonlethal and ethically flexible approaches. Since the targeted literature review for this study retrieved no metabolomics study of leucocytes, indicates that this approach, together with traditional technics and novel flow cytometry could help open new opportunities for in vitro studies in aquaculture immunology and vaccinology.

Infectious hematopoietic necrosis virus (IHNV, Rhabdoviridae), is the causative agent of infectious hematopoietic necrosis (IHN), a disease notifiable to the World Organisation for Animal Health, and various countries and trading areas (including the European Union). IHNV is an economically important pathogen causing clinical disease and mortalities in a wide variety of salmonid species, including the main salmonid species produced in aquaculture, Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss). We reviewed the scientific literature on IHNV on a range of topics, including geographic distribution; host range; conditions required for infection and clinical disease; minimum infectious dose; subclinical infection; shedding of virus by infected fish; transmission via eggs; diagnostic tests; pathogen load and survival of IHNV in host tissues. This information is required for a range of purposes including import risk assessments; parameterisation of disease models; for surveillance planning; and evaluation of the chances of eradication of the pathogen to name just a few. The review focuses on issues that are of relevance for the European context, but many of the data summarised have relevance to IHN globally. Examples for application of the information is presented and data gaps highlighted.

While the pathology peer review/pathology working group (PWG) model has long been used in mammalian toxicologic pathology to ensure the accuracy, consistency, and objectivity of histopathology data, application of this paradigm to ecotoxicological studies has thus far been limited. In the current project, the PWG approach was used to evaluate histopathologic sections of gills, liver, kidney, and/or intestines from three previously published studies of diclofenac in trout, among which there was substantial variation in the reported histopathologic findings. The main objectives of this review process were to investigate and potentially reconcile these interstudy differences, and based on the results, to establish an appropriate no observed effect concentration (NOEC). Following a complete examination of all histologic sections and original diagnoses by a single experienced fish pathologist (pathology peer review), a two-day PWG session was conducted to allow members of a four-person expert panel to determine the extent of treatment-related findings in each of the three trout studies. The PWG was performed according to the United States Environmental Protection Agency (US EPA) Pesticide Regulation (PR) 94-5 (EPA Pesticide Regulation, 1994). In accordance with standard procedures, the PWG review was conducted by the non-voting chairperson in a manner intended to minimize bias, and thus during the evaluation, the four voting panelists were unaware of the treatment group status of individual fish and the original diagnoses associated with the histologic sections. Based on the results of this review, findings related to diclofenac exposure included minimal to slightly increased thickening of the gill filament tips in fish exposed to the highest concentration tested (1,000 μg/L), plus a previously undiagnosed finding, decreased hepatic glycogen, which also occurred at the 1,000 μg/L dose level. The panel found little evidence to support other reported effects of diclofenac in trout, and thus the overall NOEC was determined to be >320 μg/L. By consensus, the PWG panel was able to identify diagnostic inconsistencies among and within the three prior studies; therefore this exercise demonstrated the value of the pathology peer review/PWG approach for assessing the reliability of histopathology results that may be used by regulatory agencies for risk assessment.

The use of nanoparticles--particles with size approximately 1-100 nm is increasing worldwide. This is particularly the case for applications of titanium dioxide nanoparticles (nano-TiO(2)) in consumer products, which have expanded at a fast rate in the last decade. The properties of nano-TiO(2) differ significantly from bulk-TiO(2) of the same composition because of an increase in surface area. A release of nano-TiO(2) from application sources to the aquatic environment may pose possible risks due to their bioavailability and toxicity. The aggregation of nano-TiO(2) plays an important role in the environmental effects of nanoparticles because the size and shape of nanoparticles will determine the magnitude of any potentially toxic effect. Aggregation is affected by pH, ionic strength, and ionic identity (inorganic and organic) of aqueous suspensions and is reviewed in this paper. The current information on the evaluation of ecotoxicological hazards of nano-TiO(2) to bacteria, algae, invertebrates, nematodes, and rainbow trout is also given.

Loma salmonae is a common gill parasite of salmonids, and essentially all species in the genus Oncorhynchus are susceptible. Infections occur in both fresh and salt water. Loma salmonae is directly transmissible by ingestion of spores or infected tissue. The parasite infects the wall of blood vessels of various organs, but the gill is the primary site of infection. Initial infection occurs in the intestine, and xenomas are easily detected in the gills by standard histology at 4-6 wk post-exposure. A few presporogonic stages of the parasite are found in the heart endothelium prior to xenoma formation in the gills. Ultrastructure studies of early infections demonstrated that wandering blood cells transport the meronts to the gills, and that merogony occurs in pillar cells and other cells underlying the gill endothelium. Xenomas develop in these cells, resulting in hypertrophied host cells filled with spores. Xenomas ultimately rupture, and are associated with severe inflammation in which free spores are found in macrophages. The parasites are most pathogenic during this phase of the infection, resulting in severe vasculitis and clinical disease. Both rainbow trout (Oncorhynchus mykiss) and Chinook salmon (Oncorhynchus ishawytscha) recover from infections, but free spores persist in kidney and spleen phagocytes for many months after xenomas are absent in Chinook salmon. Fish that have recovered from the infection show strong immunity against the parasite, lasting up to 1 year. Fish are susceptible to infection by other routes of exposure by spores; co-habitation, anal gavage, and intramuscular, intraperitoneal and intravascular injection. Autoinfection probably occurs following release of spores in blood vessels after xenomas rupture. The optimal temperature for L. salmonae infections is 15-17 degrees C, with a permissive range of 11-20 degrees C.

The paper reviews the evidence for apparent sodium-dependent copper (Cu) uptake across epithelia such as frog skin, fish gills and vertebrate intestine. Potential interactions between Na(+) and Cu during transfer through epithelial cells is rationalized into the major steps of solute transfer: (i) adsorption on to the apical/mucosal membrane, (ii) import in to the cell (iii) intracellular trafficking, and (iv) export from the cell to the blood. Interactions between Na(+) and Cu transport are most likely during steps (i) and (ii). These ions have similar mobilities (lambda) in solution (lambda, Na(+), 50.1; Cu(2+), 53.6 cm(2) Int. ohms(-1) equiv(-1)); consequently, Cu(2+) may compete equally with Na(+) for diffusion to membrane surfaces. We present new data on the Na(+) binding characteristics of the gill surface (gill microenvironment) of rainbow trout. The binding characteristics of Na(+) and Cu(2+) to the external surface of trout gills are similar with saturation of ligands at nanomolar concentrations of solutes. At the mucosal/apical membrane of several epithelia (fish gills, frog skin, vertebrate intestine), there is evidence for both a Cu-specific channel (CTR1 homologues) and Cu leak through epithelial Na(+) channels (ENaC). Cu(2+) slows the amiloride-sensitive short circuit current (I(sc)) in frog skin, suggesting Cu(2+) binding to the amiloride-binding site of ENaC. We present examples of data from the isolated perfused catfish intestine showing that Cu uptake across the whole intestine was reduced by 50% in the presence of 2 mM luminal amiloride, with 75% of the overall inhibition attributed to an amiloride-sensitive region in the middle intestine. Removal of luminal Na(+) produced more variable results, but also reduced Cu uptake in catfish intestine. These data together support Cu(2+) modulation of ENaC, but not competitive entry of Cu(2+) through ENaC. However, in situations where external Na(+) is only a few millimoles (fish gills, frogs in freshwater), Cu(2+) leak through ENaC is possible. CTR1 is a likely route of Cu(2+) entry when external Na(+) is higher (e.g. intestinal epithelia). Interactions between Na(+) and Cu ions during intracellular trafficking or export from the cell are unlikely. However, effects of intracellular chloride on the Cu-ATPase or ENaC indicate that Na(+) might indirectly alter Cu flux. Conversely, Cu ions inhibit basolateral Na(+)K(+)-ATPase and may increase [Na(+)](i).

The anticarcinogenic activity of chlorophyllin (CHL), a water-soluble derivative of chlorophyll, was first reported in rainbow trout. This review describes certain experiments which set the stage for long-term tumor bioassays, in trout and other species, using CHL and various food-borne carcinogens. Initial work with trout and rat liver enzymes in the Salmonella assay showed that CHL was a potent antimutagen towards heterocyclic amines, polycyclic aromatic hydrocarbons, aflatoxins and other classes of mutagen. Antimutagenic activity was further demonstrated using the corresponding direct-acting mutagens in the absence of an exogenous metabolizing system. Mutagen-inhibitor interaction (molecular complex formation) was identified in spectrophotometry studies, suggesting that CHL acts as an \'interceptor molecule\'. In vivo, CHL reduced hepatic AFB1-DNA adducts and hepatocarcinogenesis when the inhibitor and carcinogen were co-administered in the diet. Finally, co-injection of inhibitor and AFB1 into trout embryos established that CHL was more effective than chlorophyll a in reducing AFB1-DNA adducts 2 weeks after injection, and liver tumors after 1 year.