Histopathological effects of chronic aqueous exposure to bis(tri-n-butyltin)oxide (TBTO) to environmentally relevant concentrations reveal thymus atrophy in European flounder (Platichthys flesus)

Exposure of Cyprinus carpio var. larvae to PVC microplastics reveals significant immunological alterations and irreversible histological organ damage

Microplastics have become pervasive in ambient aquatic ecosystems over the last decade and are currently a serious global scale concern. To evaluate the potential toxic effects of PVC (polyvinyl chloride) microplastics on the immune functions of freshwater fish, this study undertook a conducted chronic 60-day dietary exposure experiment with Cyprinus carpio var. larvae. We exposed the fish to four microplastic treatments of different concentrations (food rationed diets): no-plastic (control), 10%, 20% and 30%. At the end of the experimental period the impacts of microplastics on the histology, biochemistry, ROS (reactive oxygen species) levels and gene transcription of immune organs were investigated. The results revealed that PVC microplastics induced cytoplasmic vacuolation in the liver, damaged villi in the intestine, inflammatory cell infiltration, hemosiderosis and vacuolar degeneration in the spleen, glomeruli tuft shrinkage and aggregation of melanin macrophage cells in the kidney. Moreover, following PVC microplastics exposure, ROS levels in the liver and protein levels of pro-inflammatory cytokines including IL-6, IL-8, and TNFα in the liver and serum were increased. Furthermore, modifications in the activities of non-specific immunoenzyme ACP (Acid phosphatase), AKP (alkaline phosphatase), LZM (lysozyme), and expression levels of a range of immune-related genes were observed. Using various techniques at the histological, biochemical and molecular levels, our findings demonstrated the effects of PVC microplastics on changes and imbalances in the immune status of carp. The results of this study provide basic toxicological data toward elucidating and quantifying the impacts of microplastics immunotoxicity on aquatic organisms.

Triclosan induces immunosuppression and reduces survivability of striped catfish Pangasianodon hypophthalmus during the challenge to a fish pathogenic bacterium Edwardsiella tarda

Toxicological studies on the emergent pollutant, triclosan (TCS) have established the wide-ranging effects of the compound on fish and other aquatic organisms. Although the available literature describes the standalone effects of TCS on growth and metabolism of fish yet, reports about the combined effects of TCS with microbial pathogens are scarce. In a real environment, a combined exposure to TCS and pathogens is of common occurrence, therefore, such investigation facilitates in developing a better understanding about the gross effects of pollutants and microbial pathogens on aquatic organisms including fish. In this context, the experimental fish (striped catfish, Pangasianodon hypophthalmus) were exposed to three different concentrations of TCS viz. 10, 20 and 30% of 96 h LC₅₀ (1177 μg L^-1) for 45 days including two control group firstly solvent control (without TCS) group and another one (without solvent and TCS) group in triplicate. Sampling was performed fortnightly and blood, serum and tissues (liver, and gills) samples were collected for evaluating immunological and biochemical parameters. Following 45 days of the experiments, the experimental fish in each treatment group including controls were challenged with a fish pathogenic bacterium Edwardsiella tarda (LD₅₀ dose) and fish mortality was daily monitored for calculating cumulative mortality till 7 days and further, relative per cent survivable was estimated. A significant reduction in cellular immune responses i.e. respiratory burst activity (RBA), myeloperoxidase activity (MPO), phagocytic activity (PA) and humoral immune components viz. serum lysozyme activity, total immunoglobulin in serum, ceruloplasmin level, serum total protein, albumin and globulin level was evident in TCS exposed groups in comparison to control during the experimental periods. Further, oxidative stress parameters viz. superoxide dismutase (SOD), catalase (CAT), glutathione-s-transferase (GST) activity in liver and gill tissue exhibited a dose-dependent increase in activity with related to TCS concentration during the experimental periods. A significant reduction in relative percentage survival was observed with increasing TCS concentration. The present study reveals that TCS can inhibit the cellular and humoral components of the innate immune system of the fish and can elevate the mortality due to TCS mediated immunosuppression in fish during the bacterial infection.

Response of PXR signaling pathway to simvastatin exposure in mosquitofish (Gambusia affinis) and its histological changes

As a widely used lipid lowering agent, simvastatin recently has been frequently detected in aquatic environment and the potential adverse effects from simvastatin exposure to non-target organisms such as fish is worthy of more attention. The aim of this study was to reveal the responses of detoxification system in fish to simvastatin exposure. In this investigation a ubiquitous small freshwater fish, mosquito fish (Gambusia affinis), was employed as test organism, and the transcriptional expression of nucleus transcriptional factor pregnane X receptor (PXR) and its downstream genes, including P-glycoprotein (P-gp), cytochrome 3A (CYP3A), multidrug resistance protein 2 (MRP2), UDP-glucuronosyl transferase (UGT) in mosquito fish were investigated by qRT-PCR methods under the exposure of concentrations of simvastatin (0.5 μg L-1, 5 μg L-1, 50 μgL-1, 500 μg L-1) for 24 h, 72 h and 168 h. The related enzyme activity (Erythromycin-N-Demethylase, ERND), the protein expression of PXR and the histological changes of liver tissues in fish were also determined via west blotting and transmission electron microscope approaches in the same conditions. Results showed that the mRNA expression of PXR, CYP3A and P-gp showed significantly changes under simvastatin exposure, exhibiting an obvious time/dose-effect relationship with the prolong of exposure time. ERND activity also showed time-effect at 24 h, and western blotting showed PXR protein displaying a dose-effect relationship to some extent. Hepatocyte cellular of mosquito fish exposed to simvastatin (5 μg L-1, 168 h) exhibited obvious histological changes in form of swelling, incomplete fragmentary structure etc. Overall, simvastatin altered the expression of PXR signaling pathway and subsequently bring about changes in high-levels of mosquito fish.

20 Years of fish immunotoxicology - what we know and where we are

Despite frequent field observations of impaired immune response and increased disease incidence in contaminant-exposed wildlife populations, immunotoxic effects are rarely considered in ecotoxicological risk assessment. The aim of this study was to review the literature on immunotoxic effects of chemicals in fish to quantitatively evaluate (i) which experimental approaches were used to assess immunotoxic effects, (ii) whether immune markers exist to screen for potential immunotoxic activities of chemicals, and (iii) how predictive those parameters are for adverse alterations of fish immunocompetence and disease resistance. A total of 241 publications on fish immunotoxicity were quantitatively analyzed. The main conclusions included: (i) To date, fish immunotoxicology focused mainly on innate immune responses and immunosuppressive effects. (ii) In numerous studies, the experimental conditions are poorly documented, as for instance age or sex of the fish or the rationale for the selected exposure conditions is often missing. (iii) Although a broad variety of parameters were used to assess immunotoxicity, the rationale for the choice of measured parameters was often not given, remaining unclear how they link to the suspected immunotoxic mode of action of the chemicals. (iv) At the current state of knowledge, it is impossible to identify a set of immune parameters that could reliably screen for immunotoxic potentials of chemicals. (v) Similarly, in fish immunotoxicology there is insufficient understanding of how and when chemical-induced modulations of molecular/cellular immune changes relate to adverse alterations of fish immunocompetence, although this would be crucial to include immunotoxicity in ecotoxicological risk assessment.

Exogenous 17β-oestradiol (E2) modifies thymus growth and regionalization in European sea bass Dicentrarchus labrax

The effect of 17β-oestradiol (E2) on the growth of the thymus and its regionalization into cortex and medulla was investigated in juvenile European sea bass Dicentrarchus labrax as they find themselves close to sources of oestrogenic pollution whilst residing in their estuarine nursery areas. While the exposure to 2, 20 and 200 ng l(-1) in 60 days post-hatch (dph) fish tended to cause a non-monotonous dose-response curve with a significant difference of the cortex size between lowest and highest exposures, the exposure to 20 ng l(-1) E2 from 90 dph onwards resulted in a distinct enlargement of the cortex. It is probable that the alteration of the cortex size also affects the T-cell differentiation and proliferation.

Effects of cumulative stress on fish health near freshwater outlet sluices into the sea: a case study (1988-2005) with evidence for a contributing role of chemical contaminants

Epizootic skin diseases in euryhaline flounder (Platichthys flesus) in the Dutch Wadden Sea were first reported in 1988. Particularly high prevalences of skin ulcers (up to one-third of individual fish being affected) were encountered in the vicinity of sluices draining freshwater from IJsselmeer Lake, in contrast with much lower levels in the freshwater bodies behind the sluices and open sea areas (<2%). It was proposed that salinity stress, high bacterial loads, nutritional deficiencies, and obstruction to fish migration by the sluices could all be involved in disease causation. Results of follow-up surveys at these outlet sluices from 1994 to 2005 further substantiate our preliminary findings. The follow-up data also show a general reduction in disease and improved condition factor during this period, which can be explained by improved habitat conditions for the flounder, partly due to effective sluice gate management. Furthermore, statistical correlations (p<0.05) were demonstrated between flounder ulcer occurrence and chemical contaminant concentrations in liver (Hg, Cd, Cu, Zn) and bile (the metabolite 1-OH pyrene as an indicator of chronic polycyclic aromatic hydrocarbon exposure), and histological liver lesions generally indicative of contaminant exposure (hydropic vacuolization of biliary duct epithelial cells). The findings suggest that a combination of osmotic and contaminant-induced stress also contributed to the observed disease patterns.

The effects of estrogenic and androgenic endocrine disruptors on the immune system of fish: a review

During the last decade, a number of studies have shown that, in addition to their classically described reproductive function, estrogens and androgens also regulate the immune system in teleosts. Today, several molecules are known to interfere with the sex-steroid signaling. These chemicals are often referred to as endocrine disrupting contaminants (EDCs). We review the growing evidence that these compounds interfere with the fish immune system. These studies encompass a broad range of approaches from field studies to those at the molecular level. This integrative overview improves our understanding of the various endocrine-disrupting processes triggered by these chemicals. Furthermore, the research also explains why fish that have been exposed to EDCs are more sensitive to pathogens during gametogenesis. In this review, we first discuss the primary actions of sex-steroid-like endocrine disruptors in fish and the specificity of the fish immune system in comparison to mammals. Then, we review the known interactions between the immune system and EDCs and interpret the primary effects of sex steroids (estrogens and androgens) and their related endocrine disruptors on immune modulation. The recent literature suggests that immune parameters may be used as biomarkers of contamination by EDCs. However, caution should be used in the assessment of such immunotoxicity. In particular, more attention should be paid to the specificity of these biomarkers, the external/internal factors influencing the response, and the transduction pathways induced by these molecules in fish. The use of the well-known mammalian models provides a useful guide for future research in fish.