Melano-macrophage centres and their role in fish pathology

Melanogenesis in visceral tissues ofSalmo salar. A link between immunity and pigment production?

Melanogenesis is mostly studied in melanocytes and melanoma cells, but much less is known about other pigment cell systems. Liver, spleen, kidney, and other organs of lower vertebrates harbour a visceral pigment cell system with an embryonic origin that differs from that of melanocytes. In teleosts, melanin-containing cells occur in the reticulo-endothelial system and are mainly in the kidney and spleen. The Atlantic salmon ( Salmo salar L.) is an ichthyic breeding species of considerable economic importance. The accumulation of pigments in salmon visceral organs and musculature adversely affects the quality of fish products and is a problem for the aquaculture industry. With the aim to reveal novel functions and behaviour of the salmonid extracutaneous pigment system, we investigated aspects of the melanogenic systems in the tissues of Atlantic salmon, as well as in SHK-1 cells, which is a long-term cell line derived from macrophages of the Atlantic salmon head-kidney. We demonstrate that a melanogenic system is present in SHK-1 cells, head-kidney, and spleen tissues. As teleosts lack lymph nodes and Peyer’s patches, the head-kidney and spleen are regarded as the most important secondary lymphoid organs. The detection of tyrosinase activity in lymphoid organs indicates that a link exists between the extracutaneous pigmentary system and the immune system in salmon.

CD40L--a costimulatory molecule involved in the maturation of antigen presenting cells in Atlantic salmon (Salmo salar)

The CD40L/CD40 signalling pathway is critically involved in the final stage of the maturation of DCs. This paper reports the identification and functional characterization of CD40L and CD40 from Atlantic salmon (Salmo salar). Salmon CD40L is a type II membrane-bound protein with a TNF homology domain in its extracellular C-terminal region, while CD40 is a type I membrane-bound receptor with a sequence pattern of four cysteine-rich domains in its extracellular N-terminal region. The salmon CD40L and CD40 were widely expressed, particularly in immune tissues, and while CD40L expression was induced by in vitro stimulation of HKLs with PHA and ConA, CpG increased CD40 expression. A CD40L construct was overexpressed in the CHSE-214 cell line and co-cultivation of the CD40L-CHSE transfectants with HKL induced a rapid and long-lasting upregulation of important costimulatory molecules like CD40, CD83, B7-H1 and the cytokines IL-12p40, IL-10, IL-1β and IFNs, which all are involved in T-helper cell responses. Furthermore, the CD40L transfected cells increased the percentage of HKLs expressing surface MHCIIβ but unlike other APC maturation stimuli, like CpG, they did not reduce the capacity to internalise antigen. Our results provide the first evidence for the existence of a functional CD40L mediated costimulatory pathway in Atlantic salmon.

PPARγ, an important gene related to lipid metabolism and immunity in Megalobrama amblycephala: cloning, characterization and transcription analysis by GeNorm

In order to be able to modulate and improve the function of PPARγ and decrease further some metabolic diseases of M. amblycephala, we have cloned and identified the full-length cDNA of PPARγ in M. amblycephala and examined its transcription patterns at different embryo developmental stages and in different tissues of adult and immature fish. We also accurately normalized seven reference genes by GeNorm and calculated their gene transcription normalization factors. The full-length of PPARγ was 1968 bp, consisting of 218 bp 5'-untranslated region, 1,533 bp open reading frame encoding 510 amino acids residues and 217 bp 3'-untranslated region. M. amblycephala PPARγ peptide was predicted to consist of 4 conserved domains, i.e. N-terminal domain, DNA-binding domain, ligand binding domain and flexible hinge region. PPARγ mRNAs were detected in all studied tissues of adult and immature fish including adipose tissue, gill, heart, liver, spleen, kidney, white muscle, intestine, brain and gonad. In adult fish, PPARγ transcription in liver was highest, followed by gills and it was lowest in female gonads. Moreover, the differences among liver, gill, intestine/brain, spleen/white muscle, kidney and female gonads were greatly significant (p<0.01). The transcription of PPARγ in male gonads was significantly higher than in female gonads (p<0.01). In immature fish, the transcription of PPARγ was highest in intestines followed by adipose tissue, and it was lowest in hearts and white muscles. A great difference was observed (p<0.01) in the transcription of PPARγ among adipose tissue, intestines, liver and heart/white muscles. At different embryo developmental stages, PPARγ transcription in unfertilized spermatozoa was greatly higher than in unfertilized ovum (p<0.01) and it was highest among different embryo developmental stages. The transcription of PPARγ increased gradually during 2 cells stage and 32 cells stage and then decreased until gastrula stage at which it was lowest. The transcription of PPARγ increased again on first day after hatching. There was a significant difference (p<0.01) in the transcription of PPARγ between 2 cells stage and 32 cells stage and it was same between 32 cells stage and gastrula stage. These results revealed that transcription of PPARγ showed a tissue-dependent regulation and a developmental-stage-dependent regulation that are valuable and helpful to improve the function of PPARγ and to decrease some metabolic diseases in the culture of M. amblycephala.

Metals concentrations in Nile tilapia Oreochromis niloticus () from illegal fish farm in Al-Minufiya Province, Egypt, and their effects on some tissues structures

This study clarified the suitability of fishes caught from illegal fish farms to human consumption and their hazards to public health. For this purpose, the concentrations of some metals (Al, Cd, Pb, Hg and Ni) in water and Nile tilapia (Oreochromis niloticus) fish samples collected from an illegal fish farm, in addition to pathological conditions of the fish tissues, were examined. The illegal farm water was found to be heavily polluted with metals which far exceeded the permissible limits. It was found that metals accumulated in tissues of O. niloticus in concentrations higher than those of farm water. Kidney of O. niloticus contained the highest concentrations of the detected metals, while muscle and skin contained the lowest concentrations. The examination of fish tissues revealed various histopathological lesions which related directly to the pollution of the illegal farm water. Moreover, metals levels in O. niloticus muscle were higher than the maximum permissible levels for human consumption. Consequently, the flesh of fishes from the illegal farms could be considered hazardous to human health. Therefore, warning against eating fish caught from the illegal fish farms should be announced. Moreover, removal of such illegal fish farms is necessary for the public health protection.

Pigment-producing granulomatous myopathy in Atlantic salmon: a novel inflammatory response

Melanin comprises a complex group of pigmented polymers whose primary function is ascribed to dermal solar protection, but may also have an interesting role in innate immunity. In ectothermic vertebrates, melanogenesis is reported in leukocyte populations, but it is not known if this occurs in connection with inflammatory reactions. Melanin accumulations in ectopic locations, in particular muscle, represent a serious quality problem in salmon production. Here, we investigated such changes for the expression of dopachrome tautomerase and tyrosinase as well as some important immune genes and pathogens. Furthermore, the nature of the pathological changes was addressed by morphological methods. Gene transcripts encoding key enzymes in melanogenesis, suggesting a de novo melanin synthesis in pigmented muscle, were found. MHC class II transcripts were up-regulated and there was no indication of bacterial or viral infection. The histological examination revealed granulomatous inflammation with distribution of MHC class II positive cells and T cells, analogous to the pattern found in mammals. Importantly, in contrast to mammals pigmented cells were contributing in the inflammation. We demonstrate that melanin production occurs in granulomatous inflammation in salmon, revealing a close and hitherto unreported link between the pigmentary and immune systems.

Characterisation and expression analysis of the rainbow trout (Oncorhynchus mykiss) homologue of the human dendritic cell marker CD208/lysosomal associated membrane protein 3

LAMP3/CD208 is a member of the lysosomal-associated membrane protein family and is used as a putative marker for mature dendritic cells (DCs) in humans since it is upregulated upon DC activation and maturation. This paper reports the cloning and sequencing of LAMP3 in rainbow trout. The predicted trout LAMP3 shares the characteristic features of LAMP family members such as a C-terminal lysosomal sorting motif (G-Y-D-R-I) in the short C-terminal cytoplasmic tail, typical for lysosomal targeting, four potential N-linked glycosylation sites (NXS/T), four conserved cysteines in the membrane-proximal domain and the luminal domain divided by a serine/proline-rich region. Expression studies revealed that trout LAMP3, like chicken LAMP3, was constitutively expressed in a wide range of lymphoid tissues, at highest levels in the head kidney, liver and spleen, respectively. LAMP3 was also constitutively expressed in trout head kidney macrophages and RTS11 cells and the expression was shown to be induced in vivo after infection with viral and bacterial pathogens and in cultured macrophages after modulation with microbial mimics (LPS and PolyIC). Thus, it is clear that if LAMP3 is expressed by trout DCs it is not exclusively expressed by them. However, the marker is valuable to further study antigen presentation in fish and to complement already known DC markers.

First report of a toxic Nodularia spumigena (Nostocales/ Cyanobacteria) bloom in sub-tropical Australia. II. Bioaccumulation of nodularin in isolated populations of mullet (Mugilidae)

Fish collected after a mass mortality at an artificial lake in south-east Queensland, Australia, were examined for the presence of nodularin as the lake had earlier been affected by a Nodularia bloom. Methanol extracts of muscle, liver, peritoneal and stomach contents were analysed by HPLC and tandem mass spectrometry; histological examination was conducted on livers from captured mullet. Livers of sea mullet (Mugil cephalus) involved in the fish kill contained high concentrations of nodularin (median 43.6 mg/kg, range 40.8-47.8 mg/kg dry weight; n = 3) and the toxin was also present in muscle tissue (median 44.0 μg/kg, range 32.3-56.8 μg/kg dry weight). Livers of fish occupying higher trophic levels accumulated much lower concentrations. Mullet captured from the lake 10 months later were also found to have high hepatic nodularin levels. DNA sequencing of mullet specimens revealed two species inhabiting the study lake: M. cephalus and an unidentified mugilid. The two mullet species appear to differ in their exposure and/or uptake of nodularin, with M. cephalus demonstrating higher tissue concentrations. The feeding ecology of mullet would appear to explain the unusual capacity of these fish to concentrate nodularin in their livers; these findings may have public health implications for mullet fisheries and aquaculture production where toxic cyanobacteria blooms affect source waters. This report incorporates a systematic review of the literature on nodularin measured in edible fish, shellfish and crustaceans.

Effects of herbicides and the chytrid fungus Batrachochytrium dendrobatidis on the health of post-metamorphic northern leopard frogs (Lithobates pipiens)

Effects of exposure to contaminants such as pesticides along with exposure to pathogens have been listed as two major contributors to the global crisis of declining amphibian populations. These two factors have also been linked in explanations of the causes of these population declines. We conducted a combined exposure experiment to test the hypothesis that exposure to two agricultural herbicides would increase the susceptibility of post-metamorphic northern leopard frogs (Lithobates pipiens) to the amphibian fungal pathogen Batrachochytrium dendrobatidis (Bd). We assessed the independent and interactive effects of these exposures on the health and survival of the frogs. Wild-caught frogs underwent a 21-day exposure to a nominal concentration of either 2.1 μg/L atrazine (Aatrex(®) Liquid 480) or 100 μg a.e./L glyphosate (Roundup(®) Original), followed by Bd, and then were observed until 94 days post-initial exposure to the herbicides. Actual levels of atrazine were between 4.28 ± 0.04 μg/L and 1.70 ± 0.26 μg/L while glyphosate degraded from 100 μg a.e./L to approximately 7 μg a.e./L within 6 days of initial exposure to the herbicides. Compared to controls, the glyphosate formulation reduced the snout-vent length of frogs during the pesticide exposure (at Day 21), and the atrazine formulation reduced gain in mass up to Day 94. No treatment affected survival, splenosomatic or hepatosomatic indices, the densities and sizes of hepatic and splenic melanomacrophage aggregates, the density and size of hepatic granulomas, proportions of circulating leucocytes, the ratio of neutrophils to lymphocytes, or the ratio of leucocytes to erythrocytes. Histological assessment of samples collected at Day 94 revealed no evidence of Bd infection in any Bd-exposed frogs, while real-time PCR detected only one case of light infection in a single atrazine- and Bd-exposed frog. Frogs exposed to Bd shed their skin significantly more frequently than Bd-unexposed frogs, which may have helped them resist or clear infection, and could explain why no interaction between the herbicides and Bd was detected. The results suggest that these frogs were resistant to Bd infection and that pre-exposure to the herbicides did not alter this resistance. The effects seen on the growth following herbicide exposure is a concern, as reduced growth can lower the reproductive success and survival of the amphibians.

Liver histopathology of the sharptooth catfish Clarias gariepinus as a biomarker of aquatic pollution

This paper reports on a comparative perspective of liver histopathological data of the sharptooth catfish Clarias gariepinus. The data was collected from a spectrum of relatively un-impacted and isolated, to polluted, eutrophic freshwater ecosystems. Results were compared between regional areas, by combining data from freshwater systems which has a similar pollution status and/or is located within the same geographical region. Measurements included necropsy observations, semi-quantitative liver histopathology (Liver Index), and selected biometrical indices. The aim was to establish whether the results of these measurements would differ between, and/or reflect the pollution status of, the different freshwater aquatic ecosystems. The histopathological analysis showed a higher prevalence of toxicopathic non-neoplastic, and pre-neoplastic alterations in C. gariepinus from the polluted sites. We also found a significant difference between the Liver Index, hepatosomatic index, and condition factor values of fish inhabiting impoundments known to be polluted, compared to the same species from the selected reference sites. Fish from polluted sites also had more macroscopic liver abnormalities. The results suggest that the liver histopathology of this bio-indicator fish species could be a useful biomarker of freshwater aquatic pollution.

The impact of an oil spill on organs of bream Abramis brama in the Po River

An oil spill into the River Lambro occurred on 23 February 2010 and reached the Po River the following day. Breams captured here on 1 March 2010, along with a sample from a control site, were examined by light and electron microscopy. The main affected organs were skin and gill with slight or no damage to liver, kidney, and intestine. The gills exhibited lamellar aneurisms, fusion of secondary lamellae, edema with epithelial lifting, mucous cell hypertrophy, and mucus hypersecretion. Significantly higher mucous cell density was observed in the skin of exposed fish. Histochemical staining revealed that acid glycoconjugates were prevalent in epidermal mucous cells in the exposed Abramis brama, whereas neutral and mixed glycoconjugates were dominant in the control fish. Rodlet cells were significantly more abundant in the kidney of exposed fish and showed ultrastructural differences compared to controls. These histopathologic effects were indicators of chemical stress due to exposure to oil. The present study is one of the first which explores the acute effects of this incident and makes part of a few reports focused on freshwater oil spill.

Adrenergic regulation of the innate immune response in common carp (Cyprinus carpio L.)

Catecholamines exert their physiological actions through α and β adrenergic receptors (ARs). As ARs are not exclusively expressed on neuroendocrine cells, but also on leukocytes, they may facilitate neuroendocrine modulation of immune responses. We sequenced the β(2a)-AR in common carp, and studied its expression profile and involvement in the regulation of teleost innate immune responses. β(2a)-AR messenger RNA was found to be constitutively expressed in brain areas, especially in the preoptic nucleus (NPO, homologous to the mammalian hypothalamus), and in immune organs. During the active phase of an in vivo inflammatory response, induced by i.p. zymosan treatment, β(2a)-AR gene expression was up-regulated in the peritoneal leukocytes. Additionally, adrenaline in vitro reduced the synthesis of oxygen radical species and nitric oxide, while it enhanced arginase activity in fish phagocytes. Furthermore, in vitro adrenaline administration inhibited expression of pro-inflammatory cytokines, chemokines and their receptors. It is therefore hypothesized that adrenaline will down-regulate phagocyte skewing toward classical/innate polarization.

Histologic, immunologic and endocrine biomarkers indicate contaminant effects in fishes of the Ashtabula River

The use of fish as sentinels of aquatic ecosystem health is a biologically relevant approach to environmental monitoring and assessment. We examined the health of the Ashtabula River using histologic, immunologic, and endocrine biomarkers in brown bullhead (BB; Ameiurus nebulosus) and largemouth bass (Micropterus salmoides) and compared fish collected from a reference site (Conneaut Creek). Seasonal analysis was necessary to distinguish differences in fish between the two rivers. Overall BB from the Ashtabula River had a lower condition factor and significantly more macrophage aggregates than those from the reference site. Reduced bactericidal and cytotoxic-cell activity was observed in anterior kidney leukocytes from both BB and largemouth bass from the Ashtabula River. Lower plasma thyroxine and triiodo-L-thyronine in both species in the Ashtabula River indicated disruption of the thyroid axis. Differences in physiological biomarker responses were supported by body burden chemical concentrations when data were analyzed on a seasonal basis. The use of two fish species added a level of rigor that demonstrated biological effects were not exclusive to a single species. The results provide strong evidence that contaminants have affected fish in the Ashtabula River, a Great Lakes Area of Concern, and provide a baseline by which to evaluate remediation activities.

Defining terminally differentiating B cell populations in rainbow trout immune tissues using the transcription factor XbpI

The nature of antibody-secreting cells in the rainbow trout is poorly defined. Here we describe a flow cytometric approach to help differentiate between four major trout B cell subsets present during terminal B cell differentiation: resting B cells, activated B cells, plasmablasts, and plasma cells. To aid in the identification of B cell subsets, the LPS-inducible transcription factor XbpI-S was used as a marker. An antibody specific to the stable form of inducible transcription factor X-box protein I (XbpI) was generated, which detects XbpI-S protein expression for species within the Oncorhyncus genus, including rainbow trout. Combinatorial expression patterns, or B cell signatures, were established using antibodies to XbpI-S, Pax5, and IgM in combination with a proliferation marker. We show that XbpI-S induction in trout splenic B cells increases throughout a 10-day in vitro LPS-induction period and that increased XbpI-S expression correlates with increased HCmu expression in the cell. PBLs displayed a lower level of XbpI-S induction during this incubation period, compared to spleen. We conclude that trout B cells follow a highly conserved B cell activation pathway, albeit slower than what has been observed in mammalian species. The use of XbpI-S as an activation marker for trout humoral immune activation promises to be useful for future in vivo studies, and can be applied to a broad range of teleost species.

Laser ablation ICP-MS Co-localization of mercury and immune response in fish

Mercury (Hg) contamination is a global issue with implications for both ecosystem and human health. In this study, we use a new approach to link Hg exposure to health effects in spotted gar (Lepisosteus oculatus) from Caddo Lake (TX/LA). Previous field studies have reported elevated incidences of macrophage centers in liver, kidney, and spleen of fish with high concentrations of Hg. Macrophage centers are aggregates of specialized white blood cells that form as an immune response to tissue damage, and are considered a general biomarker of contaminant toxicity. We found elevated incidences of macrophage centers in liver of spotted gar and used a new technology for ecotoxicology studies, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), to colocalize aggregates and Hg deposits within the tissue architecture. We conclude that Hg compromises the health of spotted gar in our study and, perhaps, other fish exposed to elevated concentrations of Hg.

Activation-induced cytidine deaminase structure and functions: a species comparative view

In the ten years since the discovery of activation-induced cytidine deaminase (AID) there has been considerable effort to understand the mechanisms behind this enzyme's ability to target and modify immunoglobulin genes leading to somatic hypermutation and class switch recombination. While the majority of research has focused on mouse and human models of AID function, work on other species, from lamprey to rabbit and sheep, has taught us much about the scope of functions of the AID mutator. This review takes a species-comparative approach to what has been learned about the AID mutator enzyme and its role in humoral immunity.

Assessment of the acute toxicity of the organochlorine pesticide endosulfan in Cichlasoma dimerus (Teleostei, Perciformes)

The organochlorine insecticide endosulfan (ES) is widely used despite its high toxicity to fish (96-h LC(50) median value of 2.6 μg L(-1)). This study aimed to assess the acute toxicity, histological and physiological parameters after exposure to 0; 0.25; 1; 2; 3; 4 and 16 μg L(-1) ES for 96 h under semi-static conditions in a freshwater perciform fish, Cichlasoma dimerus. Prior to death, fish exhibited behavior indicative of neurotoxicity. No difference was found in brain AChE activity. A decrease in erythrocyte mean corpuscular volume, mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration in exposed fish suggests a state of anemia. Histological alterations observed in exposed fish included hyperplasia of the interlamellar epithelium, blood congestion in secondary lamellae, and mucous cells hyperplasia and hypertrophy in gills; pycnotic nuclei and hydropic degeneration in liver; testicular damage. These moderate pathological responses in major organs could become crucial during reproduction and under prolonged exposure periods.

The effect of artificial feed on blood biochemistry profile and liver histology of wild saddled bream, Oblada melanura (Sparidae)

Floating fish farms attract a great number of wild fish species, changing their behaviour and physiology. The saddled bream, Oblada melanura, sampled from populations aggregated around the Adriatic fish farm and from natural/control populations, were analysed for differences in eleven blood biochemistry parameters and liver histomorphology. The levels of lactate dehydrogenase (LDH), alkaline phosphatase (ALKP) and urea (URE) in cage-associated saddled bream (428.00±SD 321.56 U/L, 86.13±SD 39.87 U/L and 0.05±SD 0.16 mmol/L, respectively) were significantly lower than those observed in the control specimens (1047.06±SD 505.56 U/L, 125.75±SD 34.70 U/L and 1.99±SD 0.73 mmol/L, respectively). In contrast to that, concentrations of aspartate aminotransferase (AST) in cage-associated fish (87.63±SD 132.34 U/L) were higher than values noted for the control population (6.55±SD 5.90 U/L). URE and AST presented the main variables contributing to the discrimination between two analysed populations. One-way ANOSIM based on the blood parameters showed significant difference between saddled bream that fed around cages and those from the remote waters (R=0.697; P < 0.01). Hepatocytes of cage-associated fish contained large cytoplasmatic clear spaces indicating excessive accumulation of fat in the hepatocyte cytoplasm. All observed differences can be attributed to contrasting feeding behaviour of sampled populations but basic nutritional differences between them should be quantified in the future. Moreover, further research is necessary to detect their impact on the health status of the fish.

Evaluation of oxidative stress biomarkers in Zosterisessor ophiocephalus from the Venice Lagoon, Italy

Several studies carried out in the last years have demonstrated the presence of a wide range of contaminants in some areas of the Venice Lagoon. Many of these contaminants are able to drive free radical reactions, which lead to oxidative stress and can potentially affect fish health. In the present study, oxidative stress biomarkers were examined in three different sites (Porto Marghera, Val di Brenta and Caroman) of the Venice Lagoon and their levels monitored in Zosterisessor ophiocephalus, one of the most common fish species present in the lagoon. Schmorl's staining revealed the presence of melanomacrophage centres in spleen and head kidney, and the highest number of melanomacrophage centres was observed in the animals sampled at the Porto Marghera (Porto Marghera vs Val di brenta and Caroman: p<0.01). The cellular localization of HNE and NT, investigated through an immunohistochemical approach, showed that immunopositivity was mainly localized in melanomacrophage centres of spleen and kidney. It is relevant that the animals of the detoxified control group did not exhibit any immunoreactivity. By Western blot, the antibodies against HNE and NT recognized in the liver polypeptides damaged by oxidative stress with molecular weights under 66kDa. Comparing the relative densities, animals from the Val di Brenta site exhibited the lowest levels of HNE adducts (p<0.05), whereas animals from the Porto Marghera site exhibited the highest levels of NT adducts (p<0.05). MDA levels, measured spectrophotometrically by TBARS assay did not exhibit any statistical difference among sites.

Endocrine modulation, inhibition of ovarian development and hepatic alterations in rainbow trout exposed to polluted river water

Under laboratory conditions, female rainbow trout were exposed to graded concentrations of water from the River Lambro, a polluted tributary of the River Po, and to the effluent of a large wastewater treatment plant which flows into the River Lambro. In field exposures, trout were held in cages in the River Po upstream and downstream from the confluence of the River Lambro. After 10-day (laboratory) and 30-day (laboratory and field) exposures, trout were examined for several chemical, biochemical and histological endpoints. The results indicated that exposure to complex mixtures of chemicals, including estrogen receptor agonists, aryl-hydrocarbon receptor agonists, and probably antiandrogens, had occurred. Exposure altered the plasma levels of 17β-estradiol and testosterone, and some treatments also enhanced the activity of hepatic ethoxyresorufin O-deethylase. Gonadal histology showed varying levels of degenerative processes characterised by oocyte atresia, haemorrhages, melano-macrophage centres (MMCs), and oogonia proliferation. Liver histology showed less severe effects.

Mortality of centrarchid fishes in the Potomac drainage: survey results and overview of potential contributing factors

Skin lesions and spring mortality events of smallmouth bass Micropterus dolomieu and selected other species were first noted in the South Branch of the Potomac River in 2002. Since that year morbidity and mortality have also been observed in the Shenandoah and Monocacy rivers. Despite much research, no single pathogen, parasite, or chemical cause for the lesions and mortality has been identified. Numerous parasites, most commonly trematode metacercariae and myxozoans; the bacterial pathogens Aeromonas hydrophila, Aeromonas salmonicida, and Flavobacterium columnare; and largemouth bass virus have all been observed. None have been consistently isolated or observed at all sites, however, nor has any consistent microscopic pathology of the lesions been observed. A variety of histological changes associated with exposure to environmental contaminants or stressors, including intersex (testicular oocytes), high numbers of macrophage aggregates, oxidative damage, gill lesions, and epidermal papillomas, were observed. The findings indicate that selected sensitive species may be stressed by multiple factors and constantly close to the threshold between a sustainable (healthy) and nonsustainable (unhealthy) condition. Fish health is often used as an indicator of aquatic ecosystem health, and these findings raise concerns about environmental degradation within the Potomac River drainage. Unfortunately, while much information has been gained from the studies conducted to date, due to the multiple state jurisdictions involved, competing interests, and other issues, there has been no coordinated approach to identifying and mitigating the stressors. This synthesis emphasizes the need for multiyear, interdisciplinary, integrative research to identify the underlying stressors and possible management actions to enhance ecosystem health.

The cellular context of AID expressing cells in fish lymphoid tissues

It has long been held that the cold-blooded vertebrates lack mammalian-like germinal centers, though they do have affinity maturation and the immunoglobulin mutator activation-induced cytidine deaminase or AID. Using AID as a marker of sites of somatic hypermutation, we have identified discrete cell clusters of up to several thousand cells, in the spleen and kidney of channel catfish (Ictalurus punctatus), which may be primordial germinal centers. In situ hybridization revealed that AID expressing cells are interspersed or surrounded by a population of pigmented CSF1-R expressing cells called melano-macrophages. Significantly, melano-macrophages or associated reticular cells have been previously noted for their ability to retain soluble antigen on or near their surface for several weeks following vaccination. Laser capture microdissection and RT-PCR were used to establish that these cell clusters also contained cells expressing Ig heavy chain transcripts as well as transcripts of TcRbeta and the putative CD4 homologue of fish. These observations, coupled with past work showing that mutations develop in B-cell lineages in fishes, allow us to develop a model for how affinity maturation may have evolved in early gnathostome vertebrates.

DNA damage, severe organ lesions and high muscle levels of As and Hg in two benthic fish species from a chemical warfare agent dumping site in the Mediterranean Sea

The aim of the present study was to evaluate the environmental threat to benthic species from chemical weapons dumped in the southern Adriatic Sea. An ecotoxicological approach using chemical analysis and biological responses was applied, in two sentinel species: the Blackbelly rosefish Helicolenus dactylopterus and European conger Conger conger. Specimen were collected in a stretch of sea, where had been dumped war materials and from a reference site free of ordnance. Residues of yperite, Hg and As were measured in fish fillets. Skin, liver, kidney and spleen were examined for histopathological and macroscopical lesions. Liver detoxifying capacities (EROD and UDPGT) and genotoxicity (comet assay) were also investigated. As and Hg levels were three-four times higher than those from the reference site in both species (p<0.001). Both species captured in dumping site showed clear signs of chronic illness according to the health assessment index (HAI). Deep ulcers and nodules were observed on skin and external organs. Histological lesions such as periportal and bile duct fibrosis, pericholangitis, steatosis, granuloma and elevated splenic MMCs were detected in liver and spleen. Significantly higher EROD activities were also found in both species from dumping site (p<0.01). Comet assay revealed genotoxicty in gills of C. conger from dumping site, indicating uptake of chemical warfare agents through fish gills. European conger was found to be a more sensitive bioindicator of this type of contamination than the Blackbelly rosefish.

CpG-induced secretion of MHCIIbeta and exosomes from salmon (Salmo salar) APCs

Major histocompatibility complex class II (MHCII) is encoded by polymorphic genes present in vertebrates and expressed predominately in leukocytes. Upon leukocyte differentiation, intracellular MHCII is dynamically redistributed within the cells and it is expressed at maximal levels on mature antigen presenting cells (APCs). In addition, APCs secrete MHCII within endosome-derived vesicles known as exosomes which possess diverse immunomodulatory properties. Genetic and biochemical data have confirmed that piscine leukocytes express the MHCII components as well as costimulatory molecules that are necessary for the function of APCs. However data concerning the biosynthesis and the distribution of the MHCII complex within leukocytes of lower vertebrates is scarce. The presented data demonstrates for the first time that salmon leukocytes secrete vesicles that contain exosomal markers and the abundance of MHCII indicates that these exosomes are released by APCs. The secretion was specifically induced by CpG stimulation in vitro and it was observed only in head kidney leukocytes but not in splenocyte cultures. Flow cytometry revealed that, unlike splenocytes, the majority of the MHCII-positive head kidney leukocytes were Ig-negative and a population of cells expressing high levels of surface MHCII underwent degranulation upon CpG stimulation suggesting that the MHCII-containing exosomes were derived from maturing salmon APCs. Gene expression analyses have further demonstrated that CpG-B, despite its relatively weak proinflammatory activity compared to LPS, induced expression of a larger group of genes involved in regulation of the adaptive immune response.

Distinct organ-specific up- and down-regulation of IGF-I and IGF-II mRNA in various organs of a GH-overexpressing transgenic Nile tilapia

Several lines of GH-overexpressing fish have been produced and characterized concerning organ integrity, growth, fertility and health but few and contradictory data are available on IGF-I that mediates most effects of GH. Furthermore, nothing is known on IGF-II. Thus, the expression of both IGFs in liver and various extrahepatic sites of adult transgenic (GH-overexpressing) tilapia and age-matched wild-type fish was determined by real-time PCR. Both IGF-I and IGF-II mRNA were found in all organs investigated and were increased in gills, kidney, intestine, heart, testes, skeletal muscle and brain of the transgenics (IGF-I: 1.4-4-fold; IGF-II: 1.7-4.2-fold). Except for liver, brain and testis the increase in IGF-I mRNA was higher than that in IGF-II mRNA. In pituitary, no significant change in IGF-I or IGF-II mRNA was detected. In spleen, however, IGF-I and IGF-II mRNA were both decreased in the transgenics, IGF-I mRNA even by the 19-fold. In agreement, in situ hybridisation revealed a largely reduced number of IGF-I mRNA-containing leukocytes and macrophages when compared to wild-type. These observations may contribute to better understanding the reported impaired health of GH-transgenic fish. Growth enhancement of the transgenics may be due to the increased expression of both IGF-I and IGF-II in extrahepatic sites. It is also reasonable that the markedly enhanced expression of liver IGF-II mRNA that may mimick an early developmental stage is a further reason for increased growth.

Lateral line depigmentation (LLD) in channel catfish, Ictalurus punctatus (Rafinesque)

Head and lateral line erosion (HLLE) is a chronic dermatopathy affecting a number of fish that presents as depigmented skin along the lateral line system of the trunk and head. We present microbiological, immunological and histopathological features of this lesion in channel catfish, Ictalurus punctatus (Rafinesque), that developed after exposure to a chronic nutritional stress. Depigmention was limited to skin that was adjacent to the lateral line. The epidermis of affected fish was thin and reduced to a one-cell-thick layer over the lateral line. Melanocytes were depleted at the dermo-epidermal junction and formed aggregates in the epidermis. Innate immunity was weaker in affected fish than that previously measured in well-fed channel catfish. Because the pathology and apparent aetiology of HLLE described in various fish species are highly variable, HLLE appears to be a clinical sign, rather than a disease or syndrome. Thus, we propose that this clinical sign be referred to as lateral line depigmentation (LLD), because this description more accurately encompasses all cases of this presentation reported in fish. As nutritional requirements of channel catfish and lateral line neuroanatomy are well-known, the ability to reproducibly induce LLD in this species could provide a useful model for understanding its pathogenesis.

Chronic exposure to low concentration of arsenic is immunotoxic to fish: role of head kidney macrophages as biomarkers of arsenic toxicity to Clarias batrachus

The present study was aimed at elucidating the effect of chronic low-level arsenic exposure on the head kidney (HK) of Clarias batrachus and at determining the changes in head kidney macrophage (HKM) activity in response to arsenic exposure. Chronic exposure (30 days) to arsenic (As(2)O(3), 0.50 microM) led to significant increase in arsenic content in the HK accompanied by reduction in both HKM number and head kidney somatic index (HKSI). Arsenic induced HK hypertrophy, reduction in melano-macrophage population and increased hemosiderin accumulation. Transmission electron microscopy of 30 days exposed HKM revealed prominent endoplasmic reticulum, chromatin condensation and loss in structural integrity of nuclear membrane. Head kidney macrophages from exposed fish demonstrated significant levels of superoxide anions but on infection with Aeromonas hydrophila were unable to clear the intracellular bacteria and died. Exposure-challenge experiments with A. hydrophila revealed that chronic exposure to micromolar concentration of arsenic interfered with the phagocytic potential of HKM, helped in intracellular survival of the ingested bacteria inside the HKM inducing significant HKM cytotoxicity. The immunosuppressive effect of arsenic was further evident from the ability of A. hydrophila to colonize and disseminate efficiently in exposed fish. Enzyme linked immunosorbent assay indicated that chronic exposure to arsenic suppressed the production of pro-inflammatory 'IL-1beta like' factors from HKM. It is concluded that arsenic even at very low concentration is immunotoxic to fish and the changes observed in HKM may provide a useful early biomarker of low-level xenobiotic exposure.

Retention of the cyanobacterial neurotoxin beta-N-methylamino-l-alanine in melanin and neuromelanin-containing cells--a possible link between Parkinson-dementia complex and pigmentary retinopathy

beta-N-methylamino-l-alanine (BMAA), a neurotoxic amino acid produced by cyanobacteria, has been suggested to be involved in the etiology of a neurodegenerative disease complex which includes Parkinson-dementia complex (PDC). In PDC, neuromelanin-containing neurons in substantia nigra are degenerated. Many PDC patients also have an uncommon pigmentary retinopathy. The aim of this study was to investigate the distribution of (3)H-BMAA in mice and frogs, with emphasis on pigment-containing tissues. Using autoradiography, a distinct retention of (3)H-BMAA was observed in melanin-containing tissues such as the eye and neuromelanin-containing neurons in frog brain. Analysis of the binding of (3)H-BMAA to Sepia melanin in vitro demonstrated two apparent binding sites. In vitro-studies with synthetic melanin revealed a stronger interaction of (3)H-BMAA with melanin during synthesis than the binding to preformed melanin. Long-term exposure to BMAA may lead to bioaccumulation in melanin- and neuromelanin-containing cells causing high intracellular levels, and potentially changed melanin characteristics via incorporation of BMAA into the melanin polymer. Interaction of BMAA with melanin may be a possible link between PDC and pigmentary retinopathy.

Application of in situ detection techniques to determine the systemic condition of lymphocystis disease virus infection in cultured gilt-head seabream, Sparus aurata L

Immunohistochemistry (IHC) and in situ hybridization (ISH) techniques have been used for the detection of lymphocystis disease virus (LCDV) in formalin-fixed, paraffin-embedded tissues from gilt-head seabream, Sparus aurata L. Diseased and recovered fish from the same population were analysed. IHC was performed with a polyclonal antibody against a 60-kDa viral protein. A specific digoxigenin-labelled probe, obtained by PCR amplification of a 270-bp fragment of the gene coding the LCDV major capsid protein, was used for ISH. LCDV was detected in skin dermis and gill lamellae, as well as in several internal organs such as the intestine, liver, spleen and kidney using both techniques. Fibroblasts, hepatocytes and macrophages seem to be target cells for virus replication. The presence of lymphocystis cells in the dermis of the skin and caudal fin, and necrotic changes in the epithelium of proximal renal tubules were the only histological alterations observed in fish showing signs of the disease.

Histopatologia de fígado, rim e baço de piaractus mesopotamicus, prochilodus lineatus e pseudoplatystoma fasciatum parasitados por myxosporídios, capturados no Rio Aquidauana, Mato Grosso do Sul, Brasil

Este estudo descreveu a histopatologia de rim, baço e fígado de Piaractus mesopotamicus, Prochilodus lineatus e Pseudoplatystoma fasciatum, parasitados por mixosporídios, capturados no Rio Aquidauana, MS. Após necropsia, amostras do fígado, rim cefálico e baço foram colhidas, fixadas em formalina a 10 % tamponada e processadas de acordo com a rotina histológica. Os cortes foram feitos à espessura de 5 μm e corados com hematoxilina-eosina. Foram encontrados Myxobolus porofilus em P. lineatus, M. colossomatis em P. mesopotamicus e Myxobolus spp. nas três espécies de hospedeiros. Cistos de mixosporídios no exame histopatológico foram vistos no fígado e baço de P. mesopotamicus. Mais de 50% das amostras de fígado de P mesopotamicus e P lineatus apresentou hepatodistrofia difusa. Mais de 80 % das amostras de fígado de P. fasciatum apresentou formações hialinas concêntricas e esteatose em 50% das amostras. Em 95,23 % das amostras de rins de P. mesopotamicus, foram observadas alterações teciduais, e em mais de 60 % dos casos nefrodistrofia difusa moderada e congestão de sinusóides glomerulares. Alterações teciduais nas amostras de rins de P. lineatus foram observadas em menos de 20 % da amostra. No baço dos peixes ora examinados não foram encontradas lesões dignas de relato.

Relations between and among contaminant concentrations and biomarkers in black bass (Micropterus spp.) and common carp (Cyprinus carpio) from large U.S. rivers, 1995-2004

Environmental contaminant and biomarker monitoring data from major U.S. river basins were summarized for black bass (Micropterus spp.) and common carp (Cyprinus carpio) sampled over a nine year period. Cumulative frequency distributions revealed taxon differences for many organochlorine residue concentrations, elemental contaminant concentrations, and biomarkers, but few gender differences were evident for chemical concentrations. Concentrations of dacthal, pentachloroanisole, p,p'-DDE, endosulfan sulfate, barium, cadmium, copper, manganese, lead, selenium, vanadium, and zinc were greater in carp than bass, but concentrations of mercury and magnesium were greater in bass. Gender differences were evident in bass for mercury and in carp for zinc, but the differences were small compared to taxon differences. Greater vitellogenin concentrations, 17beta-estradiol concentrations, 17beta-estradiol/11-ketotestosterone ratios, and percent oocyte atresia in female carp compared to female bass may be related to the sequential spawning of carp. Regression analyses indicated that as much as 78% of biomarker variation was explained by chemical contaminant concentrations. Sites grouped consistently by river basin in the chemical contaminant principal components analysis (PCA) models and were driven by mercury, magnesium, barium, mirex, and oxychlordane. PCA models for the biomarkers did not group the sites by basin for either bass or carp. Statistical analyses and data interpretation were limited by the study design. The implications of these limitations are discussed. Recommendations to be considered during the planning of future monitoring studies include the exclusion of gender- and species-specific sampling for certain chemical contaminants considering analytical methods with appropriate sensitivities; and allowing for the addition of new chemical and biological variables as methods and information needs evolve.

First evidence of polybrominated diphenyl ether (flame retardants) effects in feral barbel from the Ebro River basin (NE, Spain)

Polybrominated diphenyl ethers (PBDEs) are chemicals of environmental concern due to their lipophilic, persistent and bioaccumulable characteristics as well as for their potential endocrine disrupting role. Former studies carried out in a tributary of the Cinca river (Ebro basin, NE Spain) revealed high levels of PBDEs in fish due to the discharges of effluents rich in PBDEs coming from a nearby industrial park in Barbastro. In this study, several biomarkers of pollutants exposure were measured in barbel, Barbus graellsii, before (upstream) and after (downstream) the main industrial site (Barbastro) in the Vero river. The results evidenced an enhanced hepatic phase I and II metabolism (measured as reductases, glutathione S transferase and uridinediphospho-glucuronosyltransferase), and of the antioxidant enzyme glutathione peroxidase. Conversely, fishes collected from downstream reaches had their phase I CYP1A dependent ethoxyresorufin O-deethylase, antioxidant diaphorase and brain cholinesterase activities depleted. In addition, the histological study of the liver and kidney of these fish evidenced an increase of the number and size of macrophage aggregates in most individuals collected downstream. Bivariate correlated analyses showed that the above mentioned biomarkers were correlated to measured PBDE congeners, thus indicating that the observed biological effects were unlikely to be related to other environmental factors than PBDEs. Overall, the measured biochemical and histological markers provide new evidence that in field exposed fish, PBDEs levels were associated with high activities of phase I and II metabolic enzymes, oxidative stress in liver, neurotoxicity in brain and histopathological effects in both liver and kidney.

Histo-cytological responses of Dicentrarchus labrax (L.) following mercury exposure

This work deals with the damaging effects of mercury (Hg concentrations 251, 355, 501 microgl(-1)) on the structure and ultrastructure of gills, liver, intestine and kidney of farmed European sea bass (Dicentrarchus labrax L., 1758) acutely treated for 24 and 48 h. The histoarchitecture of the gills of exposed fish was highly modified due to severe oedema, telangiectasia and secondary lamellar fusion. In hepatocytes and enterocytes hydropic cell swelling, alterations to the endoplasmic reticulum and mitochondria were noted, in addition to an abundance of myelinoid bodies which were frequently encountered following treatment. In the intestine and renal tubules of exposed European sea bass, rodlet cells (RCs) displayed ultrastructural modifications. Statistical analyses were conducted on the number and the size of selected cell types and structures. Following exposure to mercury for 24 and 48 h, the number of chloride cells, RCs and macrophage aggregates were found to have increased significantly in the gills, the intestine and the head kidney.

Comparative cellular morphology suggesting the existence of resident dendritic cells within immune organs of salmonids

This report is the first morphological description of cells that resemble dendritic cells, which appear to form resident populations within the spleen and anterior kidney of fish. Based on examination of three salmonid species, including, rainbow trout, brook trout, and Atlantic salmon, the cells were most abundant in the spleen, although they were always present in the anterior kidney. The cells appeared diffusely distributed, often near blood vessels of the spleen and kidney of healthy fish and within the epithelium, connective tissue, and blood vessels of rainbow trout gills with experimentally induced microsoporidial gill disease. The dendritic-like cells in this study contained granules that resemble Birbeck granules, which are considered to be morphological markers of Langerhans cells in mammals. The cells were approximately 6 mum in diameter and contained Birbeck-like (BL) granules localized near centrioles. Although the dendritic-like cells in the three salmonid species shared many similarities, morphological differences were found in the fine structure of the rod portion of the BL granules. Rainbow trout BL granules contained amorphous material, while the other salmonid species contained particulate material arranged in a square-lattice arrangement. The BL granules in the cells of Atlantic salmon had a narrow diameter and contained four layers of particulate material when sectioned longitudinally; two layers enveloped by the granule membrane and two central layers making up a central lamella, which is common in mammalian Birbeck granules.