Melano-macrophage centres and their role in fish pathology

Liver regeneration observed across the different classes of vertebrates from an evolutionary perspective

The liver is a key organ that performs diverse functions such as metabolic processing of nutrients or disposal of dangerous substances (xenobiotics). Accordingly, it seems to be protected by several mechanisms throughout the life of organisms, one of which is compensatory hyperplasia, also known as liver regeneration. This review is a recapitulation of the scientific reports describing the different ways in which the various classes of vertebrates deal with liver injuries, where since mammals have an improved molecular toolkit, exhibit optimized regeneration of the liver compared to lower vertebrates. The main molecules involved in the compensatory process, such as proinflammatory and inhibitory cytokines, are analyzed across vertebrates with an evolutionary perspective. In addition, the possible significance of this mechanism is discussed in the context of the long life span of vertebrates, especially in the case of mammals.

Dietary uptake and effects of copper in Sticklebacks at environmentally relevant exposures utilizing stable isotope-labeled 65CuCl2 and 65CuO NPs

Copper oxide nanoparticles (CuO NPs) accumulating in sediment can be taken up by invertebrates that serve as prey for fish. Thus, it is likely that the latter are exposed to CuO NPs via the gut. However, to this day it is unknown if CuO NPs can be taken up via the gastrointestinal tract and if and in which tissues/organs they accumulate. To address this knowledge gap, we synthesized CuO NPs enriched in the stable isotope ⁶⁵Cu and incorporated them at low concentration (5 μg ⁶⁵Cu g^-1 ww food) into a practical diet prepared from worm homogenate, which was then fed to Three-spined Stickleback (Gasterosteus aculeatus) for 16 days. For comparison, fish were exposed to a diet spiked with a ⁶⁵CuCl₂ solution. Background Cu and newly taken up ⁶⁵Cu in fish tissues/organs including gill, stomach, intestine, liver, spleen, gonad and carcass and feces were quantified by ICP-MS. In addition, expression levels of genes encoding for proteins related to Cu uptake, detoxification and toxicity (ctr-1, gcl, gr, gpx, sod-1, cat, mta and zo-1) were measured in selected tissues using RT-qPCR. The obtained results showed that feces of fish fed ⁶⁵CuO NP-spiked diet contained important amounts of ⁶⁵Cu. Furthermore, there was no significant accumulation of ⁶⁵Cu in any of the analyzed internal organs, though ⁶⁵Cu levels were slightly elevated in liver. No significant modulation in gene expression was measured in fish exposed to ⁶⁵CuO NP-spiked diet, except for metallothionein, which was significantly upregulated in intestinal tissue compared to control fish. Altogether, our results suggests that dietary absorption efficiency of CuO NPs, their uptake across the gastrointestinal barrier into the organism, and effects on Cu-related genes is limited at low, environmentally relevant exposure doses (0.2 μg ⁶⁵Cu ^-1 fish ww day^-1).

Development of Fish Parasite Vaccines in the OMICs Era: Progress and Opportunities

Globally, parasites are increasingly being recognized as catastrophic agents in both aquaculture sector and in the wild aquatic habitats leading to an estimated annual loss between 1.05 billion and 9.58 billion USD. The currently available therapeutic and control measures are accompanied by many limitations. Hence, vaccines are recommended as the "only green and effective solution" to address these concerns and protect fish from pathogens. However, vaccine development warrants a better understanding of host-parasite interaction and parasite biology. Currently, only one commercial parasite vaccine is available against the ectoparasite sea lice. Additionally, only a few trials have reported potential vaccine candidates against endoparasites. Transcriptome, genome, and proteomic data at present are available only for a limited number of aquatic parasites. Omics-based interventions can be significant in the identification of suitable vaccine candidates, finally leading to the development of multivalent vaccines for significant protection against parasitic infections in fish. The present review highlights the progress in the immunobiology of pathogenic parasites and the prospects of vaccine development. Finally, an approach for developing a multivalent vaccine for parasitic diseases is presented. Data sources to prepare this review included Pubmed, google scholar, official reports, and websites.

Biological and anthropogenic influences on macrophage aggregates in white perch Morone americana from Chesapeake Bay, USA

The response of macrophage aggregates in fish to a variety of environmental stressors has been useful as a biomarker of exposure to habitat degradation. Total volume of macrophage aggregates (MAV) was estimated in the liver and spleen of white perch Morone americana from Chesapeake Bay using stereological approaches. Hepatic and splenic MAV were compared between fish populations from the rural Choptank River (n = 122) and the highly urbanized Severn River (n = 131). Hepatic and splenic MAV increased with fish age, were greater in females from the Severn River only, and were significantly greater in fish from the more polluted Severn River (higher concentrations of polycyclic aromatic hydrocarbons, organochlorine pesticides, and brominated diphenyl ethers). Water temperature and dissolved oxygen had a significant effect on organ volumes, but not on MAV. Age and river were most influential on hepatic and splenic MAV, suggesting that increased MAV in Severn River fish resulted from chronic exposures to higher concentrations of environmental contaminants and other stressors. Hemosiderin was abundant in 97% of spleens and was inversely related to fish condition and positively related to fish age and trematode infections. Minor amounts of hemosiderin were detected in 30% of livers and positively related to concentrations of benzo[a]pyrene metabolite equivalents in the bile. This study demonstrated that hepatic and splenic MAV were useful indicators in fish from the 2 tributaries with different land use characteristics and concentrations of environmental contaminants. More data are needed from additional tributaries with a wider gradient of environmental impacts to validate our results in this species.

Structure of the gonoduct of the viviparous teleost Cnesterodon decemmaculatus (Jenyns, 1842) (Poeciliidae)

During embryogenesis, teleost females do not develop Müllerian ducts, which form the oviducts in all other vertebrates. Thus, when they reach sexual maturity they do not have oviducts. In viviparous teleosts, the lack of oviducts means that the development of the embryos occurs as an intraovarian gestation, unique among vertebrates. The ovary is an unpaired hollow organ whose cavity is continuous with the caudal portion, the gonoduct, characterized by the absence of germinal cells, which opens to the exterior at the gonopore. The gonoduct attains essential function as a barrier between the germinal region of the ovary and the exterior during all reproductive stages. This study describes the functional morphology of the gonoduct in the viviparous teleost Cnesterodon decemmaculatus during non-gestation (previtellogenesis and vitellogenesis) and gestation. The ovaries were processed using histological techniques and stained with hematoxylin-eosin, and periodic acid Schiff. The gonoduct has two regions: cephalic and caudal, and is formed by three histological layers, which are, from inside to the periphery: (a) tunica mucosa; (b) tunica muscularis; and (c) tunica serosa. In the cephalic region there are mucosal folds extending into the lumen and forming a structure similar to a cervix. The histology of the gonoduct indicates essential functions, that is, (a) the control of the luminal diameter in the limit to the germinal region of the ovary by the presence of a cervix; (b) during insemination the gonoduct receives the spermatozoa, may store and transport them to the germinal region; (c) the presence of melano-macrophage centers indicates support of immunological processes, especially during gestation when these centers increase in size; (d) production of exocrine secretions; and (e) it is the birth canal, internally lined by an ciliated epithelium and surrounded by smooth musclesboth tissues supposedly supporting the birth process.

Metabolic, immunologic, and histopathologic responses on premetamorphic American bullfrog (Lithobates catesbeianus) following exposure to lithium and selenium

The presence of chemicals and the destruction of freshwater habitats have been addressed as one of the reasons for the decline in the amphibians' populations worldwide. Considering the threat that these animals have been suffering in tropical regions, the present study tested if the Brazilian legislation, concerning the permissive levels of lithium and selenium in water bodies and effluents, warrants the protection of aquatic life. To do so, we assessed the metabolic, immunologic, and histopathologic alterations in liver samples of American bullfrog (Lithobates catesbeianus), at the premetamorphic stage, through biomarkers indicative of general energetic status, i.e., glucose, lipid, and protein metabolism using biochemical and histochemical approaches. The immunologic responses were assessed by the quantification of melanomacrophage centres (MMCs); the histopathologic evaluation of the liver sections was also performed. The assay was carried out over 21 days with two periods of sampling (after 7 and 21 days) to assess the effects of exposure over time. The animals were exposed to the considered safe levels of lithium (2.5 mg L^-1) and selenium (10 μg L^-1), both, isolated and mixed. The exposed animals showed alterations in glucose and lipid metabolism throughout the experiment. The intense presence of MMCs and histopathological responses are compatible with hepatotoxicity. The toxicity expressed by the employed animal model indicates that the Brazilian environmental legislation for the protection of aquatic life needs to be updated. With this study, we intend to provide data for better environmental policies and bring attention to sublethal effects triggered by the presence of contaminants in the aquatic environment.

Changes in the Splenic Melanomacrophage Centre Surface Area in Southern Bluefin Tuna (Thunnus maccoyii) Are Associated with Blood Fluke Infections

Melanomacrophage centres (MMCs) are aggregates of macrophages accumulating various pigments. They have been proposed as an indicator of fish immune response. Blood flukes are common parasites in farmed fish. Two cohorts of wild Southern Bluefin Tuna (Thunnus maccoyi) were examined at transfer, before treatment against blood flukes (pre-treatment) and at harvest. MMCs were assessed in histological sections using image analysis, while Cardicola forsteri and Cardicola orientalis infection severity was determined using qPCR, count of adult flukes in heart flushes and count of eggs in gill filaments. Fish from both cohorts showed the same pattern in the changes in the surface area of MMCs. The surface area of splenic MMCs increased over the ranching duration and was positively correlated to the PCR determined copy numbers of Cardicola forsteri ITS2 rDNA in the gills of those fish. However, the infection with blood fluke was more variable, both between cohorts and individuals within the same cohort. Eggs of blood fluke were detected in renal MMCs using histology. Cardicola forsteri had a higher prevalence than Cardicola orientalis. This study contributes to our understanding of blood fluke infections in Southern Bluefin Tuna and their interactions with MMCs.

Anatomy of teleost fish immune structures and organs

The function of a tissue is determined by its construction and cellular composition. The action of different genes can thus only be understood properly when seen in the context of the environment in which they are expressed and function. We now experience a renaissance in morphological research in fish, not only because, surprisingly enough, large structures have remained un-described until recently, but also because improved methods for studying morphological characteristics in combination with expression analysis are at hand. In this review, we address anatomical features of teleost immune tissues. There are approximately 30,000 known teleost fish species and only a minor portion of them have been studied. We aim our review at the Atlantic salmon (Salmo salar) and other salmonids, but when applicable, we also present information from other species. Our focus is the anatomy of the kidney, thymus, spleen, the interbranchial lymphoid tissue (ILT), the newly discovered salmonid cloacal bursa and the naso-pharynx associated lymphoid tissue (NALT).

An overview of the structural and functional aspects of immune cells in teleosts

The immune system of fish consists of two main components, innate and adaptive immunities. Innate immunity is non-specific and acts as the primary line of protection against pathogen invasion, while adaptive immunity is more specific to a certain pathogen/following adaptation. The adaptive immune system consists of the humoral and cellular components. Cytotoxic T-lymphocyte cells are the major component of the cellular immunity that frequently kills viral-, bacterial- or parasitic-infected cells. According to the anatomical location, the mucosal-associated lymphoid tissue (MALT) in teleost fish subdivides into gut-associated lymphoid tissue (GALT), gill-associated lymphoid tissue (GIALT), and skin-associated lymphoid tissue (SALT). The MALTs contain various leukocytes; including, but not limited to, lymphocytes (T and B cells), plasma cells, macrophages, and granulocytes. Macrophages are multifunctional cells that are mainly involved in the immune response, including; phagocytosis and degradation of foreign antigens, tissue remodeling, and production of cytokines, chemokines and growth factors. An interesting feature of teleost macrophages is their ability to form melanomacrophage centers (MMC) in the hemopoietic tissues. Dendritic cells, rodlet cells, mast cells, eosinophilic granular cells (ECGs), telocytes, osteoclasts, club cells, as well as, barrier cells have been recorded in many fish species and have many immunological roles. This paper aims to summarize the current knowledge of the immune cells present in fish tissues serving as anatomical and physiological barriers against external hazards. Increased knowledge of fish immune systems will facilitate the development of novel vaccination strategies in fish.

Multi-biomarkers approach to access the impact of novel metal-insecticide based on flavonoid hesperidin on fish

Aquatic ecosystem health is the main concern to increasing pesticides application to control agricultural pests as it is the ultimate receptor of such materials. This study evaluated the impact of new metal-insecticide, the [Mg(hesp)₂(phen)], referred as MgHP, on fish using physiological, genetic, biochemical, and morphological biomarkers. The fish, Prochilodus lineatus, was exposed to 0 (control), 1, 10, 100, 1000 μg L^-1 MgHP, for 24 and 96 h. MgHP was not lethal but caused genotoxicity, altered hematological variables and, the activity of antioxidant and biotransformation enzymes and histology of liver, depending on concentration and time exposure. Hematocrit and erythrocyte number (RBC) increased without change hemoglobin content resulting in changes in hematimetric indexes after 24 h; after 96 h, only RBC was changed. Erythrocyte nuclear abnormalities and crenate cells increased after 24 h but, not after 96 h. Erythrocytes and hepatocytes indicated instability in DNA integrity however, the absence of micronuclei suggested DNA damage repairment. After 24 h, the antioxidant defense system and the phase II biotransformation enzyme was responsiveness and catalase activity decreased at high MgHP concentrations; the antioxidant response was triggered after 96 h. Hepatocyte hypertrophy, intracellular cytoplasmic substances, cytoplasm degeneration, melanomacrophage and hyperemia increased in fish exposed from 10 μg L^-1 to higher MgHP concentrations; the organ alteration index increased as MgHP concentration increased showing dose-dependence. Most of hematological and genotoxic effects occurred after 24 h exposure evidencing potential recover capability of organism by activation of the antioxidant defense system and DNA repairment mechanisms. Nevertheless, the histopathological changes in the liver was maintained over time at high MgHP concentrations, a concentration usually no environmental relevant. In conclusion, this data reinforced the importance of continuing research on MgHP effects in other organisms considering the promising use of such compound to control the leaf-cutter ants and other insects.

Hepatobiliary PAHs and prevalence of pathological changes in Red Snapper

Red Snapper (Lutjanus campechanus) were collected throughout the Gulf of Mexico (GoM) from 2011 to 2017 and analyzed for biliary (n = 496) fluorescent aromatic compounds (FACs), hepatic (n = 297) polycyclic aromatic hydrocarbons (PAHs) and microscopic hepatobiliary changes (MHC, n = 152). Gross and histological evaluations were conducted with liver tissues to identify and characterize pathological changes. This is the first report to interrelate hepatobiliary PAH concentrations and MHCs in Red Snapper. Hepatic PAHs measured in GoM Red Snapper ranged from 192 to 8530 ng g^-1 w.w. and biliary FACs ranged from 480 to 1,100,000 ng FAC g^-1 bile. Biliary FACs in Red Snapper collected along the west Florida Shelf and north central region declined after 2011 and were relatively stable until a sharp increase was noted in 2017. Increases in the PAH exposures are likely due to a number of sources including leaking infrastructure, annual spills, riverine input and the resuspension of contaminated sediments. In contrast, hepatic PAH concentrations were relatively stable indicating Red Snapper are able to maintain metabolic clearance however this energetic cost may be manifesting as microscopic hepatic changes (MHCs). Virtually all (99 %) of the evaluated Red Snapper had one to nine MHCs with an average of five coinciding changes in an individual fish. The observed changes were broadly classified as inflammatory responses, metabolic responses, degenerative lesions, nonneoplastic proliferation and neoplastic lesions. Biliary FACs were associated with parasitic infection and intracellular breakdown product accumulation such as intra-macrophage hemosiderin, lipofuscin and ceroid laden prevalence. Whereas, hepatic PAHs were associated with increased myxozoan plasmodia prevalence. This study evaluates relationships between hepatobiliary PAH concentrations and biometrics, somatic indices, condition factors and microscopic hepatic changes in Red Snapper located in the north central GoM. Together, these results may be signaling increased disease progression in Gulf of Mexico Red Snapper more than likely resulting from chronic environmental stressors including elevated PAH exposures and concentrations.

PRV-1 Infected Macrophages in Melanized Focal Changes in White Muscle of Atlantic Salmon (Salmo salar) Correlates With a Pro-Inflammatory Environment

Melanized focal changes in white skeletal muscle of farmed Atlantic salmon, "black spots", is a quality problem affecting on average 20% of slaughtered fish. The spots appear initially as "red spots" characterized by hemorrhages and acute inflammation and progress into black spots characterized by chronic inflammation and abundant pigmented cells. Piscine orthoreovirus 1 (PRV-1) was previously found to be associated with macrophages and melano-macrophages in red and black spots. Here we have addressed the inflammatory microenvironment of red and black spots by studying the polarization status of the macrophages and cell mediated immune responses in spots, in both PRV-1 infected and non-infected fish. Samples that had been collected at regular intervals through the seawater production phase in a commercial farm were analyzed by multiplex fluorescent in situ hybridization (FISH) and RT-qPCR methods. Detection of abundant inducible nitric oxide synthase (iNOS2) expressing M1-polarized macrophages in red spots demonstrated a pro-inflammatory microenvironment. There was an almost perfect co-localization with the iNOS2 expression and PRV-1 infection. Black spots, on the other side, had few iNOS2 expressing cells, but a relatively high number of arginase-2 expressing anti-inflammatory M2-polarized macrophages containing melanin. The numerous M2-polarized melano-macrophages in black spots indicate an ongoing healing phase. Co-localization of PRV-1 and cells expressing CD8⁺ and MHC-I suggests a targeted immune response taking place in the spots. Altogether, this study indicates that PRV-1 induces a pro-inflammatory environment that is important for the pathogenesis of the spots. We do not have indication that infection of PRV-1 is the initial causative agent of this condition.

Morphology, histology and histochemistry of the digestive tract of the Banded tilapia, Tilapia sparrmanii (Perciformes: Cichlidae)

This study described anatomical, histological and histochemical features of the mucosal layer of the digestive tract of Tilapia sparrmanii Smith, 1840, an omnivorous freshwater fish endemic to Southern Africa. This species exhibited a short thick oesophagus with long deep longitudinal folds (466.68 ± 16.91 µm), and a thick (173.50 ± 10.92 µm) muscular layer that allow the passage of large food items. The mucosa was lined with stratified secretory epithelium rich in goblet cells that secreted neutral and acid mucins. The stomach was a sac-like structure with simple tubular glands surrounded by connective tissue. The mucosa was lined with simple columnar epithelium and the lamina propria exhibited a well-developed layer of gastric glands that occupied the entire length of the cardio-fundic region. The stomach mucosa consisted of epithelial cells with intense neutral mucin secretion which protects against gastric juice. Neck cells of gastric glands synthesized neutral and acid mucins. The intestine was highly coiled and presented a complex pattern of transversal folds internally (villi). Villi length decreased progressively from the anterior to the posterior intestine (p < 0.0001). Tunica muscularis of the mid-intestine had the thinnest thickness among all parts of the intestine (p < 0.0001). Goblet cells whose numbers increased towards the rectum secreted both acid and neutral mucins. The results indicate structural similarities of T. sparrmaniiGIT with other tilapia species and will be useful for understanding the physiology of the digestive systems as well as functional components of the GIT.

Differential liver histopathological responses to amphibian chytrid infection

Amphibians have been facing a pandemic caused by the deadly fungus Batrachochytrium dendrobatidis (Bd). Although studies have elucidated cutaneous and homeostatic disturbances, it is still unknown if the hepatic function can be affected or if hepatic effects differ among host species. Thus, we evaluated the effects of an experimental Bd infection on the liver (histopathology and the hepatosomatic index) of 2 anuran species (Xenopus laevis and Physalaemus albonotatus) with different susceptibilities to Bd infection and compared them to uninfected controls. Bd infection increased the melanomacrophage cell area and induced leukocyte infiltration in both species. The effects were more pronounced in the sensitive species, P. albonotatus, which showed severe reduction in glycogen stores and liver atrophy, due to energetic imbalance. Hepatocytes of P. albonotatus also showed ballooning degeneration (vacuolization), which could lead to cell death and liver failure. Our results provide evidence that although the sensitive species showed more severe effects, the tolerant species also had hepatic responses to the infection. These findings indicate that hepatic function can play an important role in detoxification and in immune responses to chytridiomycosis, and that it may be used as a new biomarker of health status in chytrid infections.

Histological and Ultrastructural Studies of the Unique Hemopoietic-Endocrine Organ of the Grass Carp, Ctenopharyngodon idella (Valenciennes, 1844)

Specific features of the immunohistochemical and ultrastructural organization of the hemopoietic head-kidney (HK) in adult Ctenopharyngodon idella (Valenciennes, 1844) were investigated using light and transmission electron microscopy. The HK of grass carp possessed all developmental stages of leucocytes and erythrocytes, as well as dendritic cells and epithelial reticular cells. The rodlet cells were expressed α-smooth muscle actin (SMA). In addition, macrophages were the most numerous cells in the HK, which aggregated into structures called melanomacrophage centers (MMCs). On contrary, the chromaffin and interrenal cells (ICs) were mixed and organized into large anastomosing cords, which lined the posterior cardinal veins of the HK, and associated with many blood capillaries. The ICs displayed the characteristic features of steroid-producing cells. Three types of chromaffin cells: adrenaline, noradrenaline, and small granule-containing cells were observed in the HK. Glial fibrillary acidic protein (GFAP)-positive sustentacular cells were marked among the chromaffin cells. Hemopoietic cells, immune cells, MMCs, rodlet cells, in addition to three types of chromaffin cells and one type of interrenal cells in the HK were correlated with the functional significance of the fish concerned.

Histopathology changes in the rainbow trout (Onchorhyncus mykiss) consuming boric acid supplemented fish fodder

OBJECTIVE

Even though boron (B), as a trace micronutrient, occurs in natural waters and organisms, its high concentration could cause harmful and even toxic for organisms. The aim of present study was to investigate the effects of boric acid (BA) added to feed (0.01%, 0.05%, 0.10%, and 0.20% of B in feed) on Rainbow Trout (Oncorhynchus mykiss) by histopathological methods and compared to the control feed as without B.

METHODOLOGY

At the end of the feeding, after weighing the live weight of 9 rainbow trout from each group, tissue fragments were taken from the liver, gill, kidney, skeletal muscle, spleen and brains of fish, which systemic necropsies was done, and were fixed in 10 % buffered formalin solution.

RESULTS

Histopathological examinations revealed degenerative and necrotic changes in the liver, gill, kidney, skeletal muscle, spleen and brain. Hydropic and vacuolar degenerations in liver parenchyma, lamellar edema in the gills, hyaline accumulation in the kidneys, degenerations in the muscles, necrosis in the spleen and hyperemia in the brain were observed in all groups except control group. It was observed that the destruction of boric acid on fish increased depending on the amount of boron supplemented to the feed, and the most effect was in the group fed with 0.20 % boron supplemented feed.

CONCLUSIONS

The findings aside from causing pathological changes in all organs in terms of histopathological findings of Boric Acid (BA), the most severe lesions were observed in the liver.

Grass carps co-exposed to environmentally relevant concentrations of cypermethrin and sulfamethoxazole bear immunodeficiency and are vulnerable to subsequent Aeromonas hydrophila infection

The aquatic ecosystem is seriously damaged because of the heavy use of pesticides and antibiotics. Fish is the indispensable link between environmental pollution and human health. However, the toxic effects of environment-related concentrations of pesticides and antibiotics in fish have not been thoroughly studied. In this study, grass carps exposed to cypermethrin (CMN, 0.651 μg/L) or/and sulfamethoxazole (SMZ, 0.3 μg/L) for 42 days caused oxidative stress, apoptosis and immunodeficiency in the spleen of grass carps. CMN or/and SMZ exposure led to oxidative damage (consumption of antioxidant enzymes (superoxide dismutase and catalase)) and lipid peroxidation (accumulation of malondialdehyde), induced apoptosis (increases in TUNEL index, Bax/bcl-2, p53, puma and Caspase family expression). In addition, the levels of immunoglobulin M (IgM), complement 3 (C3) were significantly decreased in all treatment groups, which trend was also found in C-reactive protein in CMN and MIX group, and lysozyme in MIX group. Transcription of almost all genes involved in the Toll-like receptors (TLR) signaling pathway was up-regulated under CMN or/and SMZ exposure. However, when subsequently attacked by Aeromonas hydrophila for 2 days, the TLR pathway was inhibited in spleens of all treatment groups accompanied by higher mortality. Overall, the environmentally relevant concentration of CMN and SMZ damages the immune system, triggering oxidative stress and apoptosis in carps. And by affecting the conduction of TLR signaling pathway, CMN or/and SMZ exposure inhibits the innate immune response of fish and reducing their disease resistance. This study highlights the importance of rational and regulated use of these pesticides and antibiotics.

Relationship between Southern Bluefin Tuna, Thunnus maccoyii, melanomacrophage centres and Cardicola spp. (Trematoda: Aporocotylidae) infection

Southern Bluefin Tuna (SBT), Thunnus maccoyii, is ranched off Port Lincoln, South Australia and is Australia's second largest economic finfish aquaculture industry. The biggest threats to SBT health identified by the industry are the blood flukes Cardicola forsteri and C. orientalis (Trematoda: Aporocotylidae). Melanomacrophage centres (MMCs) are aggregations of pigmented macrophage like cells present in spleen, kidney and liver of teleost fish. The aim of this study was to quantify MMCs in SBT anterior kidney, liver and spleen to investigate changes in relation to Cardicola spp. Infection. Samples were collected at the end of ranching from pontoons where SBT were treated with PZQ and pontoons with untreated SBT. SBT MMC percentage of surface area cover was highest in SBT spleen and lowest in the liver. Significant positive correlations were identified between SBT MMC area and SBT size in all three organs (p < 0.05). MMC area and parasite infection showed significant positive correlations in the kidney and spleen for Cardicola spp. gill egg counts, and in the kidney for C. forsteri DNA from SBT hearts and gills (p < 0.05). MMCs area increased with increased intensity of Cardicola spp. Infection and MMCs have the potential to be used as an indicator to assess health effects that Cardicola spp. have on SBT.

Accumulation and depuration of dissolved hexavalent chromium and effects on the antioxidant response in bighead carp (Aristichthys nobilis)

The present study investigated the accumulation and depuration effects of hexavalent chromium (Cr⁶⁺) in ten tissues (gills, intestines, liver, kidney, blood, heart, bladder, spleen, skin and muscle) of the bighead carp (Aristichthys nobilis). Fish were exposed to graded levels of waterborne Cr⁶⁺ (0.01, 0.1, 1 and 5 mg/L) for 4, 7 and 14 days, and subsequently transferred to Cr⁶⁺-free water for 14 days. After 14-day exposure, a dose-dependent increase of Cr⁶⁺ has been observed in most tissues. While after 14-day depuration, Cr⁶⁺ contents were significantly decreased in various tissues except in kidney and spleen where Cr⁶⁺ contents significantly increased at the group of 5 mg/L. Considering that Cr⁶⁺ highly accumulated in gills, intestines, liver and kidney, the oxidative damage of Cr⁶⁺ on the four tissues were further investigated and found that the antioxidant response to Cr⁶⁺ were organ-specific. The results in this study indicated that a 14-day period is effective for accumulation and depuration of Cr⁶⁺ in bighead carp and there was no health risk of fish muscle consumption. Additionally, the delayed efflux of Cr⁶⁺ in the fish kidney and spleen indicates that high importance should be attached to them when evaluating the toxic effects and risk assessments of Cr⁶⁺.

Morphological and histological abnormalities of the neotropical toad, Rhinella arenarum (Anura: Bufonidae) larvae exposed to dexamethasone

Dexamethasone (DEX) is a glucocorticoid highly effective as an anti-inflammatory, immunosuppressant and decongestant drug. In the present study, a preliminary acute toxicity test was assayed in order to determinate DEX median-lethal, lowest-observed-effect and the no-observed-effect concentrations (LC₅₀, LOEC and NOEC, respectively) on the common toad embryos (Rhinella arenarum). Also, morphological and histological abnormalities from five body larval regions, liver melanomacrophages (MM) and glutathione S-transferase (GST) activity were evaluated in the toad larvae to characterize the chronic sublethal effects of DEX (1-1,000 µg L^-L). Results of the acute test showed that the LC₅₀ of DEX at 96 h of exposure for the toad embryos (GS 18-20) was 10.720 mg L^-g, and the LOEC was 1 µg L^-g. In the chronic assay, the larval development and body length were significantly affected. DEX exposition also induced teratogenic effects. Most frequent external abnormalities observed in DEX-treated larvae included abdominal edema and swollen body, abnormal gut coiling and visceral congestion. Intestinal dysplasia was recurrent in cross-section of all DEX-treated larvae. Neural, conjunctive and renal epithelial cells were also affected. Significant increase in liver MM number and size, and GST activity levels were also registered in DEX treatments with respect to controls. The evaluation of a variety of biomarkers provided clear evidence of toad larvae sensitivity to DEX, and the ecotoxicological risk of these pharmaceuticals, commonly found in different water bodies worldwide on aquatic animals.

A histological evaluation of pansteatitis-affected Mozambique tilapia, Oreochromis mossambicus (Peters 1852), from different geographical locations in South Africa

Pansteatitis is the leading cause for the decline in Nile crocodile populations and the sporadic mortality of fish in the Olifants River System, South Africa. To determine the prevalence of this disease in lentic systems, Mozambique tilapia, Oreochromis mossambicus, were collected from Lake Loskop, Lake Flag Boshielo, Phalaborwa Barrage and Lake Luphephe-Nwanedi. The former three impoundments are located within the main stem of the Olifants River, while the latter, which is geographically isolated and situated in the Limpopo River System, served as a reference site. Mesenteric adipose, liver, serosa of the swim bladder, gill and the skeletal muscle of fish sampled were examined for gross and microscopic evidence of pansteatitis. Microscopically observed changes were used to statistically compare pansteatitis prevalence between samples and sites. Based on histopathological evaluation, the adipose tissue in the liver, swim bladder serosa and coelom from severely debilitated individuals showed the most significant pathological changes. Lesions indicative of steatitis were observed in fish collected from Lake Loskop (75%), Lake Flag Boshielo (22%) and Lake Luphephe-Nwanedi (15%). Further investigation is warranted to understand the pervasiveness and mechanisms driving pathological changes of pansteatitis at Lake Flag Boshielo, Phalaborwa Barrage and Lake Luphephe-Nwanedi.

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

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

Necroulcerative dermatitis associated with Myxobolus dermatoulcerans n. sp. (Cnidaria: Myxobolidae) in red-bellied piranha, Pygocentrus nattereri Kner (Characiformes: Serrasalmidae), from Peru

A group of red-bellied piranha, Pygocentrus nattereri Kner, recently imported from Peru exhibited multifocal, cutaneous ulcerations with exposure of the underlying musculature. Skin scrapes yielded moderate numbers of myxospores morphologically consistent with Myxobolus Bütschli, 1882. Myxospores from these fish were morphologically and molecularly distinct from other myxobolids infecting piranha. Myxospores are pyriform to capsular with a rounded posterior and slightly rounded to tapering anterior aspect in valvular view. Myxospore bodies are 14.3-17.8 (mean 16.1) µm long and 7.6-10.3 (mean 8.9) µm wide. Polar capsules are symmetrical, slender, elongate, and measure 7.4-10.2 (mean 9.2) µm long and 2.1-3.7 (mean 3.0) µm wide. Sequence generated for the 18S rRNA gene had no direct matches to any sequence available on GenBank but demonstrated less than 89% nucleotide similarity to various published and unpublished Myxobolus spp. from Piaractus brachypomus (Cuvier) and Colossoma macropomum (Cuvier). This paper provides the morphological and molecular characterisation of Myxobolus dermatoulcerans n. sp. from red-bellied piranha and describes associated pathological lesions.

Multiorgan histopathological changes in the juvenile seabream Sparus aurata as a biomarker for zinc oxide particles toxicity

Zinc oxide nanoparticles are widely used in some domains (cosmetics, pharmaceuticals optical devices, and agricultural field) due to their physical, optical, and antimicrobial properties. However, the release of ZnO-NPs into the environment may affect organisms like fish with potential consequences for human health. Histological approaches of the acute effects of these materials on fish are scarce; thus, the present study aimed to investigate the potential toxic effects of acute exposure to ZnO particles in marine environments, by assessing histological changes in the gills, liver, spleen, and muscle of gilthead seabream (Sparus aurata) juveniles. Thus, fish were exposed for 96 h, via water, to 1 mg L-1 of ionic zinc and zinc oxide particles (1.1, 1.2, and 1.4 μm of size). Histological examination revealed gills as the most affected organ, followed by liver, muscle, and spleen. In the gills, histopathological changes included hyperplasia of epithelial cells, fusion of the secondary lamellae, and lifting of the lamellar epithelium with edema. In the liver, lipid vacuolation of several degrees, necrosis of hepatic and pancreatic tissues, blood congestion in sinusoids and hepatoportal vessels, presence of cellular infiltrate, and melano-macrophages diffusion was found. Muscle showed degeneration, atrophy, thickening and necrosis of muscle fibers with edema between them, and presence of melano-macrophages in the muscle layer. Spleen was the less damaged organ, displaying congested blood, white pulp increase/rupture, and bigger and darker melano-macrophage aggregates in the splenic stroma. These results underline that the size of particles plays a determinant role in their potential pernicious effects. A short-term exposure caused major histopathological changes in relevant organs of S. aurata juveniles, possibly affecting their function.

Comparison of the pathogenicity of Francisella orientalis in Nile tilapia (Oreochromis niloticus), Asian seabass (Lates calcarifer) and largemouth bass (Micropterus salmoides) through experimental intraperitoneal infection

Francisella orientalis is a highly virulent, emerging bacterium that causes mass mortalities in tilapia. This pathogen also affects numerous other warm-water fish species, including three-line grunt, hybrid striped bass and various ornamental fish. This study sheds light on two new species of fish that are susceptible to F. orientalis. Asian seabass and largemouth bass showed variable levels of susceptibility in a bacterial challenge experiment. After intraperitoneally injected with a dose of 10⁶  CFU/fish, a total of 64.28% and 21.42% mortalities were obtained in Asian seabass and largemouth bass, respectively. Meanwhile, Nile tilapia showed acute mortality of 100%. All fish showed typical lesions of francisellosis, including multifocal granulomas in the spleen and head kidney. Immunohistochemical analysis revealed strong positive signals inside the granulomas of all fish. The bacterial recovery in solid media from infected fish was highest in Nile tilapia (85.71%), followed by Asian seabass (35.71%) and largemouth bass (21.42%). PCR results tested 100% positive for Nile tilapia, and 78.57% and 21.42% for Asian seabass and largemouth bass, respectively. In conclusion, Asian seabass and largemouth bass are susceptible to this pathogen, which warrants new management strategies when employing predation polyculture systems of these species with tilapia.

Are anthropogenic fibres a real problem for red mullets (Mullus barbatus) from the NW Mediterranean?

Microfibres are among the most prevalent type of microplastics in marine environments. Man-made fibres derived from cellulose are distributed worldwide, but are often confused with synthetic plastic fibres and consequently neglected. All these fibres may adversely affect aquatic organisms, but their levels and potential effects in wild fish remain unknown. We analysed anthropogenic fibre (AF) ingestion in the red mullet (Mullus barbatus), at both temporal and geographical scales, to assess potential effects of these fibres on fish health condition. AFs were present in 50% of fish digestive tracts, with a mean of 1.48 AFs per individual (SD = 1.98). In Barcelona, an increase of 46% in AF ingestion was observed in 2018 compared to 2007. AF ingestion also increases by 20% when Barcelona is compared to a less urban area (the town of Blanes). Visual characterization of fibres by typologies-corroborated by Raman spectroscopy-allowed classification and identification of 88% of AFs as cellulosic (57%), and synthetic polymers (PET) (31%). In all sampling stations, the only histopathological alterations were cysts of unknown etiology, and the most abundant parasites were nematodes. None of these alterations, parasite load, or other fish health indicators (condition indices) indicate an effect of AF ingestion.

Oxidative stress, biotransformation enzymes and histopathological alterations in Nile tilapia (Oreochromis niloticus) exposed to new and used automotive lubricant oil

Lubricant oils are among oil-based products that are not fully consumed during its use, thereby producing non-biodegradable residues which can cause contamination of natural systems. This study evaluated the toxicity of new and used lubricating oil (0.01 and 0.1 mL L^-1) in adult Nile tilapia (Oreochromis niloticus), by assessing the effects on oxidative stress, biotransformation enzymes (liver and gills), and histopathological alterations on hepatic and pancreatic tissues after 3 and 7 days of exposure. Results showed that 3-days exposure to 0.1 mL L^-1 of used and new lubricating oil increased the activity of superoxide dismutase (SOD) and malondialdehyde (MDA) levels in liver of O. niloticus, respectively. In gills, catalase (CAT) was decreased in fish exposed to 0.1 mL L^-1 of non-used oil after 3 days, but pronounced increases in CAT was detected after 7 days-exposure to both new and used oil. Shorter exposure to both concentrations of new and used oil also raised glutathione-S-transferase activity (GST) in gills. Ethoxyresorufin-O-deethylase (EROD) was induced in liver of fish exposed to 0.1 mL L^-1of used oil after 3 and 7 days, however a reduced response of this enzyme was detected in gills of animals from both oil treatments. In vitro analysis showed that hepatic EROD was inhibited by lubricating oil exposures, with more pronounced responses in treatments containing used oil. Hepatic lesions, such as cytoplasmic vacuolization, nuclei abnormally, changes in hepatocytes shape, steatosis, cholestasis, eosinophilic inclusions and necrosis were mainly increased by 7 days exposure to used lubricating oil at higher concentration.

Physiological activity of Aloe vera in pacu (Piaractus mesopotamicus) inoculated with Aeromonas hydrophila

Aloe vera is a traditional medicinal plant; however, its use in fish is fairly recent. We evaluated the effects of dietary A. vera on stress, innate immunity, and energy metabolism in pacu inoculated with Aeromonas hydrophila. For 7 days, 192 fish were fed with diets supplemented with 0% (control), 0.5%, 1.0%, and 2.0% of the plant extract and then inoculated with bacteria and sampled 3, 6, and 24 h later. All concentrations of A. vera reduced basal levels of cortisol, and 1.0% reduced cortisol levels more intensely 3 h after inoculation. A. vera increased the basal respiratory activity of leukocytes/RAL (0.5 and 1.0%), increased the serum levels of lysozyme (1.0 and 2.0%) 6 h after inoculation, and increased the activity of the complement system after 3 h. Spleen somatic index/SSI increased with 1.0 and 2.0% A. vera. A. vera also promoted metabolic effects. It increased basal levels of lipids in the liver and muscle, as well as hepatosomatic index (1.0%) and, 3 h after inoculation, prevented the reduction of serum triglyceride (1.0%) and reduced the mesenteric fat (1.0%). Bacterial inoculation increased RAL from 3 to 24 h and lysozyme levels at 24 h, increased serum cholesterol at 24 h, and decreased serum triglyceride from 3 to 24 h, regardless of A. vera. We concluded that A. vera offered for only 7 days had stress-reducing effects, stimulated innate immunity, protected triglyceride levels in blood, lipid depots in the liver and muscle, and directed the energy mobilization to visceral depots.

Low oxygen: A (tough) way of life for Okavango fishes

Botswana's Okavango Delta is a World Heritage Site and biodiverse wilderness. In 2016-2018, following arrival of the annual flood of rainwater from Angola's highlands, and using continuous oxygen logging, we documented profound aquatic hypoxia that persisted for 3.5 to 5 months in the river channel. Within these periods, dissolved oxygen rarely exceeded 3 mg/L and dropped below 0.5 mg/L for up to two weeks at a time. Although these dissolved oxygen levels are low enough to qualify parts of the Delta as a dead zone, the region is a biodiversity hotspot, raising the question of how fish survive. In association with the hypoxia, histological samples, collected from native Oreochromis andersonii (threespot tilapia), Coptodon rendalli (redbreast tilapia), and Oreochromis macrochir (greenhead tilapia), exhibited widespread hepatic and splenic inflammation with marked granulocyte infiltration, melanomacrophage aggregates, and ceroid and hemosiderin accumulations. It is likely that direct tissue hypoxia and polycythemia-related iron deposition caused this pathology. We propose that Okavango cichlids respond to extended natural hypoxia by increasing erythrocyte production, but with significant health costs. Our findings highlight seasonal hypoxia as an important recurring stressor, which may limit fishery resilience in the Okavango as concurrent human impacts rise. Moreover, they illustrate how fish might respond to hypoxia elsewhere in the world, where dead zones are becoming more common.

Productive Results, Oxidative Stress and Contaminant Markers in European Sea Bass: Conventional vs. Organic Feeding

In the present study European sea bass (Dicentrarchus labrax) subjected to two different diets (organic vs. conventional) were evaluated in terms of growing performances, oxidative stress, and contaminant markers. Growing performances were evaluated using biometric measures and condition factor (K), whereas insulin-like growth factor (IGF-I and IGF-II) levels were assessed trough Real-Time PCR analysis. For oxidative stress, immunohistochemical staining for 8-hydroxy-2'-deoxyguanosine (8-OHdG) and 4-hydroxy-2-nonenal (HNE) was performed, whereas total glutathione (GSH) in blood serum was determined by an enzymatic method adapted. Cytochrome P4501A (CYP1A) and melanomacrophage centers (MMCs) were evaluated as contaminant markers trough immunohistochemical and histochemical approaches, respectively. The growing performances showed a positive trend in both groups but a greater productivity in conventional fed fish compared to the organic ones. A significant higher expression of MMCs was observed in organic vs. conventional diet fed fish. Fillet analysis showed a higher MUFA content and a lower PUFAs n-6 content in organically fed sea bass indicating that diets with a content in fatty acids closer to that of wild fish will definitely affect the fatty acid profile of the fish flesh. On the other hand, the diet composition did not seem to affect neither the oxidative stress parameters (GSH, 8-OHdG, HNE) nor the CYP1A expression.

WITHDRAWN: Structural, ultrastructural, and immunohistochemical characteristics of the cell composition of the head kidney of grass carp (Ctenopharyngodon idella)

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Exploitation of Agro-Industrial Waste as Potential Source of Bioactive Compounds for Aquaculture

The agroindustry generates a large amount of waste. In postharvest, food losses can reach up to 50%. This waste represents a source of contamination of soil, air, and bodies of water. This represents a problem for the environment as well as for public health. However, this waste is an important source of bioactive compounds, such as phenolic compounds, terpenes, and β-glucans, among others. Several biological activities have been attributed to these compounds; for example, antioxidant, antimicrobial, gut microbiota, and immune system modulators. These properties have been associated with improvements in health. Recently, the approach of using these bioactive compounds as food additives for aquaculture have been addressed, where it is sought that organisms, in addition to growing, preserve their health and become disease resistant. The exploitation of agro-industrial waste as a source of bioactive compounds for aquaculture has a triple objective-to provide added value to production chains, reduce pollution, and improve the well-being of organisms through nutrition. However, to make use of the waste, it is necessary to revalue them, mainly by determining their biological effects in aquaculture organisms. The composition of bioactive compounds of agro-industrial wastes, their biological properties, and their application in aquaculture will be addressed here.

Changes in the immune function of rainbow trout (Oncorhynchus mykiss) provide insights into strategies against BDE-47 stress

Polybrominated diphenyl ethers (PBDEs) are ubiquitous in marine ecosystems and have been suggested to bioaccumulate in aquatic food webs, with potentially negative impacts on marine organism. In this study, a 21-day experiment was performed under controlled laboratory conditions, in which 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), the most biotoxic PBDE in the marine environment, was fed to rainbow trout (Oncorhynchus mykiss) at concentrations of 50 and 500 ng g^-1 in the diet. BDE-47 significantly decreased the specific growth rate of O. mykiss and was highly concentrated in the liver and head kidney, as evidenced by increased bioaccumulation factor (BAF) values. Tissue observation revealed impairment of the microstructure of the head kidney. Important immune factors in the skin, blood and head kidney were significantly inhibited by BDE-47 treatment (p < 0.05), whereas the respiratory burst activity of macrophages was enhanced. Additionally, immune-related genes were strongly downregulated following BDE-47 exposure (p < 0.05). In a bacterial challenge, the treatment groups had much higher mortality than did the control group (p < 0.05). BDE-47 accumulated and impaired immune organs, and the hierarchy of immune responses was impaired, consequently reducing O. mykiss resistance to pathogen invasion.

Modulatory role of dietary Thymus vulgaris essential oil and Bacillus subtilis against thiamethoxam-induced hepatorenal damage, oxidative stress, and immunotoxicity in African catfish (Clarias garipenus)

Thiamethoxam (TMX) is a widely used neonicotinoid insecticide for its effective potential for controlling insects from the agricultural field, which might induce toxicity to the aquatic biota. In this study, the role of the probiotic Bacillus subtilis (BS) and a phytogenic oil extract of Thymus vulgaris essential oil (TVEO) in the modulation of thiamethoxam (TMX)-induced hepatorenal damage, oxidative stress, and immunotoxicity in African catfish (Clarias garipenus) has been evaluated. Fish were subjected to TMX (5 mg L^-1) and fed with a diet either supplemented with BS (1000 ppm) or TVEO (500 ppm). The experiment lasted for 1 month. By the end of the experiment, blood was sampled for biochemical analysis and fish organs and tissues were collected for histopathological and immunohistochemical examinations. Results showed a substantial increase of serum markers of hepatorenal damage such as the activities of aspartate transaminase (AST), alanine transaminase (ALT), and alkaline phosphatase (ALP) and levels of blood urea nitrogen (BUN) and creatinine with an obvious decrease of serum protein levels in the TMX-intoxicated group. Also, there was a considerable increase in malondialdehyde (MDA) levels and glutathione-S-transferase (GST) activity. TMX remarkably suppressed serum lysozyme activity, respiratory burst activity, and phagocytosis with a conspicuous elevation of the levels of interleukins (interleukin-1 beta (IL-1β) and interleukin-6 IL-6). The histopathological findings showed that TMX induced degenerative changes and necrosis in the gills, liver, head kidneys, and spleen of the intoxicated fish. Significant alterations of frequency, size, and area percentage of melanomacrophage centers (MMCs), decreased splenocyte proliferation, and increased number of caspase-3 immunopositive cells were also observed. Contrariwise, the concurrent supplementation of either BS or TVEO in the diets of catfish partially mitigated both the histopathological and histomorphometric lesions of the examined tissues. Correspondingly, they improved the counts of proliferating cell nuclear antigen (PCNA) and caspase-3 immunopositive splenocytes. In conclusion, the co-administration of either BS or TVEO in catfish diets partially diminished the toxic impacts of TMX. Nonetheless, the inclusion of TVEO in the diets of catfish elicited better protection than BS against TMX-induced toxicity in response to its potential anti-inflammatory, antioxidant, anti-apoptotic, and immune-stimulant effects.

The effect of different pollutants exposure on the pigment content of pigmented macrophage aggregates in the spleen of Vardar chub (Squalius vardarensis Karaman, 1928)

Pigmented macrophage aggregates (MAs) are known to change under influence of various factors, such as aging, season, starvation, and/or pollution. In this study, changes in the pigment content of the MAs in the spleen of Vardar chub (Squalius vardarensis, Karaman) (n = 129) collected in spring and autumn, from three rivers with different pollution impact was examined: Zletovska River (metals), Kriva River (metals and municipal wastewater), and Bregalnica River (municipal wastewater). Collected data revealed increased relative volume and number of MAs containing hemosiderin under the influence of metals, significant in autumn (p < .05). In chub exposed to metals combined with municipal wastewater, significant increase of lipochrome accumulation in MAs in autumn, melanin in MAs in fish captured in the spring season, and number of splenic MAs containing combination of melanin and lipochrome was noted. Volumes and number of MAs containing combination of hemosiderin and lipochrome increased in spleen of fish captured in autumn from both Zletovska River and Kriva River, most likely due to the contribution of hemosiderin and lipochrome, respectively. Values measured for the various pigments in splenic MAs in fish captured from Bregalnica River, were overall closer to the values measured for fish captured from Kriva River. Notably, melanin and lipochrome are more likely to be found in fish from waters influenced by municipal wastewater (organic pollution) and hemosiderin in fish spleen from water influenced by mining activity (heavy metals pollution).

Differences in Gene Expression Profiles of Seven Target Proteins in Third-Stage Larvae of Anisakis simplex (Sensu Stricto) by Sites of Infection in Blue Whiting (Micromesistius poutassou)

The third-stage larvae of the parasitic nematode genus Anisakis tend to encapsulate in different tissues including the musculature of fish. Host tissue penetration and degradation involve both mechanic processes and the production of proteins encoded by an array of genes. Investigating larval gene profiles during the fish infection has relevance in understanding biological traits in the parasite’s adaptive ability to cope with the fish hosts’ defense responses. The present study aimed to investigate the gene expression levels of some proteins in L3 of A. simplex (s.s.) infecting different tissues of blue whiting Micromesistius poutassou, a common fish host of the parasite in the NE Atlantic. The following genes encoding for Anisakis spp. proteins were studied: Kunitz-type trypsin inhibitor (TI), hemoglobin (hb), glycoprotein (GP), trehalase (treh), zinc metallopeptidase 13 (nas 13), ubiquitin-protein ligase (hyd) and sideroflexin 2 (sfxn 2). Significant differences in gene transcripts (by quantitative real-time PCR, qPCR) were observed in larvae located in various tissues of the fish host, with respect to the control. ANOVA analysis showed that relative gene expression levels of the seven target genes in the larvae are linked to the infection site in the fish host. Genes encoding some of the target proteins seem to be involved in the host tissue migration and survival of the parasite in the hostile target tissues of the fish host.

Immune defense parameters of wild fish as sensitive biomarkers for ecological risk assessment in shallow sea ecosystems: A case study with wild mullet (Liza haematocheila) in Liaodong Bay

Environmental monitoring is important to the health management of an ecosystem. Biomarkers are particularly relevant because they are direct indicators of any toxic effects on organisms and are cheaper to use compared with chemical indicators, especially for extremely low-level organic contaminants. Fish can be significantly affected by pollutants, given their high trophic levels in aquatic food chains. Their immune function is closely related to their survival. The present study compared immune function-related parameters of wild mullet (Liza haematocheila) samples from low (Jinzhou) and high (Yingkou) polluted sites during the pre-winter (PW) and pre-breeding (PB) periods in Liaodong Bay, to evaluate the effect of water pollution on fish health and to explore potential biomarkers of coast water pollution. Compared with Jinzhou mullet, there was a significantly higher level of hematocrit in Yingkou mullet, but a significantly lower serum lysozyme level (P < 0.001), indicating that these fish were immunosuppressed. Significant differences occurred in the spleen between the two site populations. The abnormal: normal fish ratio in Yingkou L. haematochila was significantly higher than that of Jinzhou L. haematochila (2.5 times of that of Jinzhou during PB and nine times during PW). The splenic index of male Yingkou L. haematochila was 47.2% higher than that of Jinzhou L. haematochila in PW (P = 0.001). Moreover, histological observations showed that the spleen of the former was more congestive, with increased numbers (39.6% more) of melanomacrophage centers (MMCs) and changes in pigments (hemosiderin 8.3% higher and melanin 29.4% higher), compared with the latter. The splenic MMC area of Yingkou L. haematochila was significantly smaller than that of Jinzhou L. haematochila (P < 0.05) in PB, but showed no clear difference in PW (P > 0.05). Splenic MMC number was significantly higher in individual Yingkou L. haematochila with abnormal livers compared with normal Yingkou L. haematochila during both sampling periods. The splenic MMC area in abnormal livers was approximately four times those of normal individuals during PB in Yingkou L. haematochila. The number of splenic melanomacrophages (MM) in abnormal livers was approximately nine times those of the normal livers during PW. There were also differences in pigments in normal Yingkou individuals compared with normal Jinzhou samples during PW (melanin 29.4% higher and hemosiderin 8.3% higher). Based on these results, we suggest that serum lysozyme activity, splenic MM number and MMC (both number and area), and melanin of local fish have potential as sensitive biomarkers for the assessment of coastal water pollution.

Toxicity evaluation and microbiota response of the lined sole Achirus lineatus (Chordata: Achiridae) exposed to the light petroleum water-accommodated fraction (WAF)

Exposure to contaminants might directly affect organisms and alter their associated microbiota. The objective of the present study was to determine the impact of the petroleum-water-accommodated fraction (WAF) from a light crude oil (API gravity 35) on a benthic fish species native from the Gulf of Mexico (GoM). Ten adults of Achirus lineatus (Linnaeus, 1758) were exposed to a sublethal WAF/water solution of 50% v/v for 48 hr. Multiple endpoints were measured including tissue damage, presence of polycyclic aromatic hydrocarbons (PAHs) metabolites in bile and gut microbiota analyses. Atrophy and fatty degeneration were observed in livers. Nodules and inflammation were detected in spleen, and structural disintegration and atrophy in the kidney. In gills hyperplasia, aneurysm, and gills lamellar fusion were observed. PAHs metabolites concentrations in bile were significantly higher in exposed organisms. Gut microbiome taxonomic analysis showed significant shifts in bacterial structure and composition following WAF exposure. Data indicate that exposure to WAF produced toxic effects in adults of A. lineatus, as evidenced by histological alterations and dysbiosis, which might represent an impairment to long-term subsistence of exposed aquatic organisms.

Increased melanomacrophage centres in the liver of reproductively dysfunctional female greater amberjack Seriola dumerili (Risso, 1810)

The greater amberjack Seriola dumerili is a new aquaculture fish that may display reproductive dysfunctions. During extensive follicular atresia, which is a common reproductive dysfunction in females during vitellogenesis, part of the reabsorbed yolk returns to the liver to be metabolized and recycled. Melanomacrophage centres (MMCs) are aggregates of macrophage-like cells that play a role in the destruction, detoxification and recycling of endogenous and exogenous materials, and have been associated with systemic stress. Wild and captive-reared greater amberjack were sampled in the Mediterranean Sea during two different phases of the reproductive cycle. The liver of reproductively dysfunctional captive-reared females sampled during the spawning season showed a high density of both MMCs and apoptotic cells. A weak liver anti-cytochrome P450 monooxygenase 1A immunoreactivity was observed, suggesting that the examined fish were not exposed to environmental pollutants. We propose that the observed increase in MMCs and apoptosis in captive-reared fish was related to the hepatic overload associated to the metabolism of yolk proteins reabsorbed during extensive follicular atresia. Since follicular atresia is a frequent physiological and pathological event in teleosts, we suggest that the reproductive state should be always assessed when MMCs are used as markers of exposure to stress or pollutants.

Gonad development and reproductive hormones of invasive silver carp (Hypophthalmichthys molitrix) in the Illinois River

Reproduction is a major component of an animal's life history strategy. Species with plasticity in their reproductive biology are likely to be successful as an invasive species, as they can adapt their reproductive effort during various phases of a biological invasion. Silver carp (Hypophthalmicthys molitrix), an invasive cyprinid in North America, display wide variation in reproductive strategies across both their native and introduced ranges, though the specifics of silver carp reproduction in the Illinois River have not been established. We assessed reproductive status using histological and endocrinological methods in silver carp between April and October 2018, with additional histological data from August to October 2017. Here, we show that female silver carp are batch spawners with asynchronous, indeterminate oocyte recruitment, while male silver carp utilize a determinate pattern of spermatogenesis which ceases in the early summer. High plasma testosterone levels in females could be responsible for regulating oocyte development. Our results suggest that silver carp have high spawning activity in the early summer (May-June), but outside of the peak spawning period, female silver carp can maintain spawning-capable status by adjusting rates of gametogenesis and atresia in response to environmental conditions, while males regress their gonads as early as July. The results of this study are compared to reports of silver carp reproduction in other North American rivers as well as in Asia.

Ultrastructural Evidence of Melanomacrophagic Centers and Lipofuscin in the Liver of Zebrafish (Denio rerio)

Melanomacrophagic centers (MMCs) were studied in the liver of zebrafish using transmission electron microscope (TEM). The MMCs were located in the space of Disse (SD), and their pseudopodia protruded into the lumen of sinusoids. The degree of extension of body structure of MMCs in the SD was determined by the size of the phagocytosed content. An irregular or amoeboid nucleus was present. Vacuoles were occasionally present, both, in endothelium and MMCs. The cytoplasm of MMCs showed several engulfed structures. The most common structure was the presence of mitochondria of small to giant size and distorted shape with inconspicuous cristae. The product of mitochondrial degeneration accompanied by lysosomes contributed to the formation of lipofuscins. Besides, changes were also observed in rough endoplasmic reticulum (rER), the Golgi complex, and lysosomes. Occasionally, small to large fragments of the erythrocytes were found in the cytoplasm of MMCs. The rER encompassed the mitochondria and lipid droplets forming a membrane-like structure. Golgi complex were dilated. Lysosomes fused with such membrane-bound structures contributed to the formation of the lipofuscin. The results provide evidence of the role of liver-resident MMCs of zebrafish in phagocytosis of damaged organelles, clearance of the worn-out erythrocytes, and lipofuscin formation.

Parasitological and histopathological diagnosis of a non-native fish (Oreochromis sp.) with a noticeable presence in a natural Brazilian river environment

Nile tilapia is an exotic species produced in Brazilian aquaculture. The aim of this study was to constitute a pathological diagnosis in Oreochromis sp. with a noticeable presence in a river in southern Brazil, and to verify the origin of these fish in this natural habitat, an environment with high sanitary precariousness due to discharges of industrial effluents. A total of 30 fish were collected during three sampling events and their health status was assessed by parasitological fauna survey, parasitological indices and histopathological examination of the gills, liver, spleen and kidney. Five species of monogenea were identified infesting gills and stomach: Cichlidogyrus sclerosus, C. halli, C. thurstonae, Scutogyrus longicornis and Enterogyrus cichlidarum; and 4 species of trichodinidae infesting the body surface and gills: Trichodina magna, T. compacta, T. centrostrigeata and Paratrichodina africana. The results showed differences according to the seasonality of the collection, with higher parasite count and larger tissue alterations in summer. Histopathological analysis fluctuated from moderate to severe, but necrosis prevailed in all organs and in all fish, indicating that these fish did not enjoy full health.

Comparative histology of wild-type and p53-deficient medaka (Oryzias latipes): nephrotoxic effect of ultraviolet A radiation

Ultraviolet radiation is an ecological factor that directly affects terrestrial organisms through suppression of immunity or damage to internal organs. The present study assessed the effects of ultraviolet A (UVA) radiation on the kidneys of both wild-type (WT) and p53-deficient medaka (Oryzias latipes) and evaluated which strain was more resistant to the effects of UVA. Fish were divided into four groups: control group 1 (Cwt and Cp53), kept for 3 days without UVA exposure; group 2 (1wt and 1p53), fish exposed daily to UVA for 1 h day-1 for 3 days; group 3 (2wt and 2p53), fish exposed daily to UVA for 2 h day-1 for 3 days; and group 4 (3wt and 3p53), fish exposed daily to UVA for 3 h day-1 for 3 days. Samples of tissues were obtained 24 h after UVA exposure. The most obvious histopathological changes induced by UVA radiation in kidney tissues of both strains of medaka (WT and p53-deficient) were high levels of vacuolation of tubular cells followed by necrosis. The tubular segments lost their normal shape which appeared like a network structure and their cells with clear cytoplasm. Necrosis of lymphoid tissues and spots of brown pigmentation (possibly melanomacrophages) were sporadically seen in interstitial lymphoid tissues, while shrinkage of glomeruli, diminution of periodic acid-Schiff staining, and increased amount of collagenous fibers were observed. Our results confirmed the harmful effects of UVA radiation on kidney tissues of both WT and p53-deficient medaka. However, WT medaka was affected more than p53-deficient medaka.

Polycyclic aromatic hydrocarbons in bays of the Rio de Janeiro state coast, SE - Brazil: Effects on catfishes

The Brazilian coast of the Rio de Janeiro State has bays of great economic, ecological and social importance. However, these ecosystems have been suffering intense anthropogenic influence, mainly due to the contamination by polycyclic aromatic hydrocarbons (PAHs) from urban-industrial activities. Moreover, PAHs are organic pollutants of high toxicity and carcinogenicity causing global concern to human and environmental health. This study evaluated on catfish (Genidens genidens) a set of key parameters (sex, morphometric traits, condition factor (K), PAH metabolites in gallbladder, frequency of micronucleus (MN) and erythrocytic nuclear abnormalities (ENA) in blood. In addition we also evaluated histopathological hepatic effects, Ethoxyresorufin-O-deethylase (EROD) activity and Benzo(a)pyrene diol epoxide (BPDE)-DNA adducts) in liver samples, in order to indicate the fish health status and environmental pollution levels of three main Bays (Guanabara, Sepetiba and Ilha Grande) of the Rio de Janeiro State, in the Southeast of Brazil. In general, the worst physical and metabolic conditions in catfishes were evidenced in Guanabara Bay, possibly indicating the highest level of contamination by PAHs. Contrary evidence was observed in Ilha Grande Bay, showing lower biological changes in G. genidens. However in Sepetiba Bay, the influence of PAHs contamination showed the highest hepatic lesions in catfishes, prevailing foci of cellular alterations, megalocytic hepatosis and hydropic vacuolations. The employability of a set of biomarkers on catfish was efficient for screening pollution for PAHs in tropical environments. This reinforces the need for effective actions of monitoring and conservation strategies of bays of the Rio de Janeiro State (Brazil), in order to ensure quality and health to both human and environment.

Waterborne microcystin-LR exposure induced chronic inflammatory response via MyD88-dependent toll-like receptor signaling pathway in male zebrafish

Waterborne microcystin-LR (MC-LR) released by cyanobacterial blooms in eutrophic water bodies have caused serious risk to aquatic animal and human health. In the present study, we for the first time conducted a comprehensive in vivo investigation on chronic inflammatory responses and its molecular pathways of different environmental relevant levels of MC-LR (0, 0.4, 2 and 10 μg/L) in male zebrafish (Danio rerio). The results showed that chronic MC-LR exposure caused splenic inflammatory changes including the formation of melano-macrophage centers, remarkable elevation of serum tumor necrosis factor alpha (TNFα) and interleukin 1 beta (IL1β) levels as well as significant upregulated expression of MyD88-dependent toll-like receptor (TLR/MyD88) signaling pathway genes (tlr4a, myd88, erk2, p38a, il1β and tnfα). The immunohistochemical and western blot results further validated that higher MC-LR concentrations tended to enhance the MyD88 signal. Moreover, significant decreases of serum C3 levels along with splenic c3b expression in the 10 μg/L exposure group proved that chronic MC-LR exposure could ultimately decrease the innate immunity of fish. Our findings revealed that chronic exposure of MC-LR could cause chronic inflammation through TLR/MyD88 signaling pathway and subsequently induce immune disorders in male zebrafish, which also urge us to pay more attention on the potential immunotoxicity of long-term exposure to low concentration of MC-LR.

Immunohistological Biomarkers of Toxicity by a Pharmaceutical Antidepressant in the Freshwater Cichlid Fish Cichlasoma dimerus (Teleostei, Cichliformes)

Melano-macrophage centers (MMCs) are nodular clusters of pigmented macrophages, implicated in homeostasis and destruction and recycling of endogenous and exogenous material. They can increase in size and/or frequency under environmental stress resulting in immunohistological biomarkers of water quality. Fluoxetine (FLX), a commonly prescribed antidepressant, can cause neuroendocrine, behavioral and reproductive alterations in teleost fish. In the present study, we analyzed the effects of a 2-week 50 µg/L FLX exposure on MMCs in histological sections of spleen and head-kidney (HK) of the cichlid fish Cichlasoma dimerus. In the spleen, FLX caused an increase in the area and a decrease in the number of MMCs. An increase in the proportion of the HK occupied by MMCs was observed in FLX-exposed fish, due to an increase in their number but not their area. The deposition rate of MMCs varies according to the hemolymphopoietic organ and would be the result of a differential response to FLX on homeostatic functions (elimination of cellular debris, iron processing and immune response).

Larva of greater wax moth Galleria mellonella is a suitable alternative host for the fish pathogen Francisella noatunensis subsp. orientalis

Background

Francisella noatunensis subsp. orientalis (Fno) is the etiological agent of francisellosis in cultured warm water fish, such as tilapia. Antibiotics are administered to treat the disease but a better understanding of Fno infection biology will inform improved treatment and prevention measures. However, studies with native hosts are costly and considerable benefits would derive from access to a practical alternative host. Here, larvae of Galleria mellonella were assessed for suitability to study Fno virulence.

Results

Larvae were killed by Fno in a dose-dependent manner but the insects could be rescued from lethal doses of bacteria by antibiotic therapy. Infection progression was assessed by histopathology (haematoxylin and eosin staining, Gram Twort and immunohistochemistry) and enumeration of bacteria recovered from the larval haemolymph on selective agar. Fno was phagocytosed and could survive intracellularly, which is consistent with observations in fish. Virulence of five Fno isolates showed strong agreement between G. mellonella and red Nile tilapia hosts.

Conclusions

This study shows that an alternative host, G. mellonella, can be applied to understand Fno infections, which will assist efforts to identify solutions to piscine francisellosis thus securing the livelihoods of tilapia farmers worldwide and ensuring the production of this important food source.