Liver melanomacrophage centres and CYP1A expression as response biomarkers to environmental pollution in European anchovy (Engraulis encrasicolus) from the western Mediterranean Sea

Understanding the host response of farmed fish to blood flukes (Trematoda: Aporocotylidae) for developing new treatment strategies

Aporocotylids (Trematoda: Digenea), also known as fish blood flukes infect the circulatory system of fish leading to serious health problems and mortality. Aporocotylids are a particular concern for farmed fish as infection intensity can increase within the farming environment and lead to mortalities. In the context of managing these infections, one of the most crucial aspects to consider is the host response of the infected fish against these blood flukes. Understanding the response is essential to improving current treatment strategies that are largely based on the use of anthelmintic praziquantel to manage infections in aquaculture. This review focuses on the current knowledge of farmed fish host responses against the different life stages of aporocotylids. New treatment strategies that are able to provide protection against reinfections should be a long-term goal and is not possible without understanding the fish response to infection and the interactions between host and parasite.

The influence of ecological factors in the modulation of pollution biomarkers of two small pelagic marine fish

Biomarkers are useful tools for the detection of marine pollution, which is poorly monitored in the pelagic environment. In this study, we investigated the role of key biological and environmental factors on three hepatic xenobiotic biomarkers: carboxylesterases (CEs), glutathione S-transferase (GST) and catalase (CAT). Additionally, ethoxyresorufin-O-deethylase (EROD) and benzyloxy-4-[trifluoromethyl]-coumarin-O-debenzyloxylase (BFCOD) activities were determined for comparative purposes. The pelagic species targeted were the European anchovy (Engraulis encrasicolus) and the European sardine (Sardina pilchardus). The results revealed sex-dependent CE activities in sardine. CEs and GST activities were significantly affected by reproduction and, in anchovy, CE activities were also influenced by temperature. In vitro incubations revealed that the pesticide dichlorvos caused up to 90 % inhibition of basal CEs activity. This work highlights that the reproductive status, temperature and sex, modulate biomarker responses, and that anchovy would be more suitable pelagic bioindicator due to its higher in vitro sensitivity to dichlorvos and sex-independent biomarker responses.

A Novel, Highly Potent NADPH-Dependent Cytochrome P450 Reductase from Waste Liza klunzingeri Liver

The use of marine enzymes as catalysts for biotechnological applications is a topical subject. Marine enzymes usually display better operational properties than their animal, plant or bacterial counterparts, enlarging the range of possible biotechnological applications. Due to the fact that cytochrome P450 enzymes can degrade many different toxic environmental compounds, these enzymes have emerged as valuable tools in bioremediation processes. The present work describes the isolation, purification and biochemical characterization of a liver NADPH-dependent cytochrome P450 reductase (CPR) from the marine fish Liza klunzingeri (LkCPR). Experimental results revealed that LkCPR is a monomer of approximately 75 kDa that is active in a wide range of pH values (6-9) and temperatures (40-60 °C), showing the highest catalytic activity at pH 8 and 50 °C. The activation energy of the enzyme reaction was 16.3 kcal mol^-1 K^-1. The K_M values for cytochrome C and NADPH were 8.83 μM and 7.26 μM, and the k_cat values were 206.79 s^-1 and 202.93 s^-1, respectively. LkCPR displayed a specific activity versus cytochrome C of 402.07 µmol min^-1 mg¹, the highest activity value described for a CPR up to date (3.2-4.7 times higher than the most active reported CPRs) and showed the highest thermostability described for a CPR. Taking into account all these remarkable catalytic features, LkCPR offers great potential to be used as a suitable biocatalyst.

A Window of Vulnerability: Chronic Environmental Stress Does Not Impair Reproduction in the Swordfish Xiphias gladius

Xiphias gladius is an important fishing resource. The Mediterranean stock is affected by overfishing and is declining. In this light, the aim of this study was to evaluate the cross-talk among metabolism, stress response, immune system and reproduction in immature and mature females, coupling histological and transcriptomic approaches. The transcriptome of livers from 3 immature and 3 mature females was analyzed using the Artificial Intelligence RNA-Seq. For the histological analysis, ovary and liver samples were collected from 50 specimens caught during the reproductive season in the Mediterranean Sea. A total of 750 genes were differentially expressed between the livers. The gene ontologtabey analysis showed 91 upregulated and 161 downregulated biological process GO terms. Instead, the KEGG enrichment analysis revealed 15 enriched pathways. Furthermore, the binding occurring between estrogen receptors and aryl hydrocarbon receptor nuclear translocator, upregulated in mature females, could be liable for the inhibition of detoxification pathway. Indeed, at the histological level, mature females showed a higher density and number of melanomacrophage centers, biomarkers of stress. The present findings reveal the cross-talk among response to environmental stressors, metabolism and reproduction, highlighting that mature females invest a lot of energy in reproduction instead of immune response and detoxification.

Assessment of the health status of the European anchovy (Engraulis encrasicolus) in the NW Mediterranean Sea from an interdisciplinary approach and implications for food safety

The European anchovy (Engraulis encrasicolus) is a small pelagic fish with an outstanding commercial value supporting important fisheries and is a key component of pelagic ecosystems in the Mediterranean Sea. Progressive reductions in the population size of this species has been observed in the Mediterranean Sea during recent decades, accompanied by a decline in the body condition, as well as the size/age of maturation. Nonetheless, the health status has not been yet assessed using a holistic approach. Herein, we analyse the health status of the European anchovy, integrating distinct indicators from fish condition, enzymatic biomarkers, presence of tissue alterations, and parasite descriptors. In addition, we analyse the presence of anthropogenic items (AIs) in the digestive tract of fish and their potential impact on health status. Additionally, we assess the differences between current AIs values and those recorded over 12 years ago. None of the health indicators studied provided evidence of relevant pathologic conditions affecting this fish species in the studied area. However, changes in the pattern of liver parenchyma were found. Compared with anchovy populations from other distribution areas, no zoonotic parasites were recorded in this study, demonstrating a reduced risks associated with foodborne transmission to humans. AIs, such as fibres and plastic particles, were found in the digestive tract of half of the fish analysed. A significant increase was detected in AIs prevalence between 2007 (40 %) and 2019 (70 %), alongside differences in the abundance and typology of the AIs, though this does not seem to have impacted fish health yet. Therefore, our work underscores the importance of implementing a regular program to monitor the health status of this key species to better understand population dynamics and their drivers.

Aggregation of hepatic melanomacrophage centers in S. herzbergii (Pisces, Ariidae) as indicators of environmental change and well-being

ABSTRACT The melanomacrophage centers (MMCs) in the liver of fish are indicators of environmental conditions, as they are involved in xenobiotic biotransformation. The objective of this study was to evaluate the number of MMC in the liver of juveniles and adults of Sciades herzbergii from areas with different levels of contamination. The fish were caught at three points (reference - A1, potentially impacted - A2 and contaminated - A3), in São José bay (Maranhão, Brazil), in four samples. The livers were subjected to the standard histological procedure and 5μm sections were stained with hematoxylin-eosin. In livers of A2 adult individuals (260.50±161.50 MMCs / mm²) they presented a greater number of MMCs when compared to A3 adults (60.00 ± 30.10 MMCs / mm²). Juveniles showed considerable values in A1 (100.00 ± 0.00 MMCs/mm²) and A2 (95.33 ± 33.00 MMCs / mm²) compared to juveniles in A3 (49.00±0.00 MMCs/mm²). These high values are unexpected for young people. The average number of MMC correlated with the rainy season in the region. The use of hepatic MMCs as a biomarker of exposure to pollutants, in particular substances from fisheries systems, such as ammonia and nitrite, proved to be adequate to differentiate areas with different levels of impacts.

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.

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.

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.

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.

Evidences of possible influences of methylmercury concentrations on condition factor and maturation of Lophius vomerinus (Cape monkfish)

Muscle and liver tissues of Lophius vomerinus off the coast of Namibia were analysed to investigated the influence of MeHg on the biological parameters of L.vomerinus by (i) determining if the variability in total MeHg concentrations is influenced by length, maturity status and sex, and (ii) assessing if there is a relationship between biological indices (Condition factor (K), Gonadosomatic Index (GSI) Hepatosomatic Index (HSI)) and MeHg concentrations. Correlations between total MeHg concentrations and fish length, K and HSI were observed. A weak positive correlation was observed between total MeHg and GSI for combined sex. Total MeHg concentration in tissues of L. vomerinus is significantly dependent on the maturity stages (p < 0.05). K was significantly inversely correlated with total MeHg in tissues of L. vomerinus. The evidence presented in this study suggests that MeHg in L. vomerinus tissues could be detrimental to both its physiology and population dynamics.

Uncommon hepatic macrophagic foamy-cell nodules in Iberian barbel (Luciobarbus bocagei Steindachner, 1864) from the Vizela River (Portugal)

The main intent of this work (after the by chance finding, in archived histological slides) is to characterize one previously non-described liver lesion of the Iberian barbel from the Vizela River (Portugal). This ran through a textile and dyeing industrial region. The lesion type was made of groups of foamy cells (presumptive macrophages), which appear either as a "smaller non-nodular form," without a connective tissue capsule and displaying an irregular profile, or as a "bigger nodular form," presenting a thin capsule and a circular profile. The nodular forms could appear multi-layered, resembling "cross-sectioned onions". The lesions number, dimension, and structural complexity were greater in bigger fish, appearing only after a history of poor water quality. In extreme cases, the lesions slightly protruded the liver surface. Special histological staining proved the connective tissue nature of the capsule (and its eventual septa), the presence of proteins, glycoproteins, lipofuscin, melanin, iron (putative hemosiderin), and copper, in a variable number of foamy cells within the lesions. At times, degenerating hepatocytes appeared at the border of the lesions. It is proposed that this lesion type incorporates both macrophages and degenerating hepatocytes, looking as one (unpublished) form of a macrophage aggregate. The term "foamy-cell nodules" was advanced for this abnormality. The lesion could have been induced by pollution, because: no parasites were ever associated with the lesion; there was co-existence of the lesion with a water quality status scored as "bad"; such lesion neither existed in fish sampled after mitigation and remediation measures nor in reference fish.