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Parabens are preservatives widely used in personal care products, pharmaceuticals, and foodstuffs. However, they are still unregulated chemical compounds. Given their extensive use and presence in different environmental compartments, parabens can adversely affect animal health. Thus, the current study aimed to summarize and critically analyze the bioaccumulation and ecotoxicity of parabens in aquatic species. Studies have been mostly conducted in laboratory conditions (75%), using mainly fish and crustaceans. Field studies were carried out across 128 sampling sites in six countries. Paraben bioaccumulation was predominantly detected in fish muscle, liver, brain, gills, ovary, and testes. Among the parent parabens, methylparaben (MeP), ethylparaben (EtP), and propylparaben (PrP) have been detected frequently and more abundantly in tissues of marine and freshwater specimens, as well as the metabolite 4-hydroxybenzoic acid (4-HB). Parabens can induce lethal and sublethal effects on aquatic organisms, such as oxidative stress, endocrine disruption, neurotoxicity, behavioral changes, reproductive impairment, and developmental abnormalities. The toxicity of parabens varied according to species, taxonomic group, developmental stage, exposure time, and concentrations tested. This study highlights the potential bioaccumulation and ecotoxicological impacts of parabens and their metabolites on aquatic invertebrates and vertebrates. Additionally, future research recommendations are provided to evaluate the environmental risks posed by paraben contamination more effectively., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Thimerosal, a preservative commonly used in the pharmaceutical and cosmetic industry, has raised concerns regarding its potentially toxic effects as an organic mercury compound. Within this context, using an NMR-based metabolomics profile and chemometric analysis, zebrafish embryos were used as an in vivo model to study the effects of thimerosal in metabolic profiles after exposure to sublethal concentrations of the mercury compound. The thimerosal concentrations of 40 and 80 nM were employed, corresponding to 40% and 80% of the LC 50 , respectively, for zebrafish embryos. The most significant alterations in the metabolic profile included changes in carbohydrates, amino acids, nucleotides, trimethylamine-N-oxide, ethanolamine, betaine, and ethanol. Furthermore, thimerosal exposure affects various metabolic pathways, impairing the nervous system, disrupting protein metabolism, and potentially causing oxidative damage. Therefore, adopting a metabolomics approach in this investigation provided insights into the potentially implicated metabolic pathways contributing to the deleterious effects of thimerosal in biological systems., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

There is a growing concern regarding the adverse risks exposure to cylindrospermopsin (CYN) might exert on animals and humans. However, data regarding the toxicity of this cyanotoxin to neotropical fish species are scarce. Using the fish species Poecilia reticulata , the influence of CYN concentrations equal to and above the tolerable for drinking water may produce on liver was determined by assessing biomarkers of antioxidant defense mechanisms and correlated to qualitative and semiquantitative histopathological observations. Adult females were exposed to 0.0 (Control); 0.5, 1 and 1.5 μg/L pure CYN for 24 or 96 hr, in triplicate. Subsequently the livers were extracted for biochemical assays and histopathological evaluation. Catalase (CAT) activity was significantly increased only by 1.5 μg/L CYN-treatment, at both exposure times. Glutathione -S-transferase (GST) activity presented a biphasic response for both exposure times. It was markedly decreased after exposure by 0.5 μg/L CYN treatment but significantly elevated by 1.5 μg/L CYN treatment. All CYN treatments produced histopathological alterations, as evidenced by hepatocyte cords degeneration, steatosis, inflammatory infiltration, melanomacrophage centers, vessel congestion, and areas with necrosis. Further, an I ORG >35 was achieved for all treatments, indicative of the presence of severe histological alterations in P. reticulata hepatic parenchyma and stroma. Taken together, data demonstrated evidence that CYN-induced hepatotoxicity in P. reticulata appears to be associated with an imbalance of antioxidant defense mechanisms accompanied by histopathological liver alterations. It is worthy to note that exposure to low environmentally-relevant CYN concentrations might constitute a significant risk to health of aquatic organisms.

Coral reefs are experiencing accelerated degradation due to global and local stressors. The understanding of how corals cope with these disturbances is urgent. We focused on elucidating antioxidant capacity responses of the Mussismilia harttii and Siderastrea sp. corals, in reefs with use management in a marine protected area. We tested whether the activity of antioxidant enzymes in healthy colonies is higher at multiple-use reefs than at no-take reef, and whether the activity of antioxidant enzymes is higher for bleached than for healthy Siderastrea sp. colonies. Lipid peroxidation and enzymatic activity found in bleached colonies evidence chronic stress and cellular damage not related to thermal anomalies. Chronic stress in healthy colonies was also found but responses differed among species, being higher at multiple use reefs, mainly for Siderastrea sp. We highlight the role of the local conservation actions in the integrity of coral physiology and reef resilience under global climate changes., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Taciana Kramer de Oliveira Pinto reports equipment, drugs, or supplies and travel were provided by National Council for Scientific and Technological Development. Taciana Kramer de Oliveira Pinto reports equipment, drugs, or supplies and travel were provided by Coordination of Higher Education Personnel Improvement. Taciana Kramer de Oliveira Pinto reports equipment, drugs, or supplies and travel were provided by Fundação de Amparo a Pesquisa do Estado de Alagoas., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Metabolomics is an innovative approach used in the medical, toxicological, and biological sciences. As an interdisciplinary topic, metabolomics and its relation with the environment and toxicological research are extensive. The use of substances, such as drugs and pesticides, contributes to the continuous releasing of xenobiotics into the environment, harming organisms and their habitats. In this context, fish are important bioindicators of the environmental condition and have often been used as model species. Among them, zebrafish (Danio rerio) presents itself as a versatile and straightforward option due to its unique attributes for research. Zebrafish proves to be a valuable model for toxicity assays and also for metabolomics profiling by analytical tools. Thus, NMR-based metabolomics associated with statistical analysis can reasonably assist researchers in critical factors related to discovering and validating biomarkers through accurate diagnosis. Therefore, this review aimed to report the studies that applied zebrafish as a model for (eco)toxicological assays and essentially utilized NMR-based metabolomics analysis to assess the biochemical profile and thus suggest the potential biological marker., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Nuclear abnormality (NA) assay in fish has been widely applied for toxicity risk assessment under field and laboratory conditions. The zebrafish (Danio rerio) has become a suitable model system for assessing the NA induced by pollutants. Thus, the current study aimed to summarize and discuss the literature concerning micronucleus (MN) and other NA in zebrafish and its applications in toxicity screening and environmental risk assessment. The data concerning the publication year, pollutant type, experimental design, and type of NA induced by pollutants were summarized. Also, molecular mechanisms that cause NA in zebrafish were discussed. Revised data showed that the MN test in zebrafish has been applied since 1996. The MN was the most frequently NA, but 15 other nuclear alterations were reported in zebrafish, such as notched nuclei, blebbed nuclei, binucleated cell, buds, lobed nuclei, bridges, and kidney-shaped. Several pollutants can induce NA in zebrafish, mainly effluents (mixture of pollutants), agrochemicals, and microplastics. The pollutant-induced NA in zebrafish depends on experimental design (i.e., exposure time, concentration, and exposure condition), developmental stages, cell/tissue type, and the type of pollutant. Besides, research gaps and recommendations for future studies are indicated. Overall, the current study showed that zebrafish is a suitable model to assess pollutant-induced mutagenicity., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The cyanotoxin cylindrospermopsin (CYN) is the second biggest cause of poisoning worldwide, both in humans and animals. Although CYN primarily affects the aquatic environments and can be absorbed in fishes by multiple routes, data reporting its toxicity and mechanism of action are still scarce in this group. Using P. reticulata as model species, it was evaluated whether CYN promotes mutagenic and genotoxic effects in different fish target tissues. Adult females were exposed in a static way to 0 (control), 0.5, 1.0, and 1.5 μg L -1 of pure CYN for 24 and 96 hours. For the first time, DNA damage was detected in fish brain after CYN exposition. In brain cells, a concentration-response DNA damage was observed for both exposure times, suggesting a direct or indirect action of CYN in neurotoxicity. For the liver cells, 96 hours caused an increase in DNA damage, as well the highest percentage of DNA in the tail was reached when used 1.5 μg L -1 of CYN. In peripheral blood cells, an increase in DNA damage was observed for all tested concentrations after 96 hours. In erythrocytes, micronuclei frequency was higher at 1.5 μg L -1 treatment while the erythrocyte nuclear abnormalities (ENA) frequency was significantly higher even at the lowest CYN concentration. Such data demonstrated that acute exposition to CYN promotes genotoxicity in the brain, liver, and blood cells of P. reticulata, as well mutagenicity in erythrocytes. It rises an alert regarding to the toxic effects of CYN for aquatic organisms as well as for human health., (© 2021 Wiley Periodicals LLC.)

The objective of this study was to establish a protocol for the characterization, isolation, and culture of type A spermatogonia using specific molecular markers for these cells in fish. To this end, adult Prochilodus lineatus testes were collected and digested enzymatically and the resulting testicular suspension was separated using a discontinuous Percoll gradient, followed by differential plating. The cell cultures obtained were monitored for 15 days and analyzed using the immunofluorescence method with anti-Vasa, anti-GFRα1, and anti-OCT4 antibodies. Spermatogonial enrichment was also performed using flow cytometry. Although discontinuous Percoll gradient centrifugation followed by differential plating enabled the removal of differentiated germ cells and somatic cells, enriching the pool of type A spermatogonia, the enrichment of type A spermatogonia through flow cytometry of samples without Percoll proved to be more efficient. Prominent cell agglomerates that were characterized according to different stem cell markers as type A spermatogonia were observed during the 15 days of the cell culture. The use of immunoperoxidase and western blot analysis methods confirmed the specificity of the markers for type A spermatogonia of P. lineatus. When combined with specific cell culture conditions, the positive characterization of these molecular markers clarified certain aspects of spermatogonial regulation, such as survival and proliferation. Finally, understanding the regulation of the in vitro germ cell maintenance process may contribute to the enhancement of in vivo and in vitro reproduction techniques of endangered or aquaculture fish species., (© 2020 Wiley Periodicals LLC.)

Gonadotropin-releasing hormone (GnRH) is a key molecule in the initiation of the hypothalamic-pituitary-gonadal axis. Thus, knowledge about GnRH may contribute to the effectiveness of species reproduction. Using a Neotropical tetra Astyanax altiparanae as a fish model species, the GnRH forms were characterized at the molecular level and the role of injected GnRHs in vivo was evaluated. The full-length complementary DNA (cDNA) sequences of preproGnRH2 (612 bp) and preproGnRH3 (407 bp) of A. altiparanae were obtained, and the GnRH1 form was not detected. The cDNA sequences of preproGnRH2 and preproGnRH3 were found to be conserved, but a change in the amino acid at position 8 of the GnRH3 decapeptide of A. altiparanae was observed. All the injected GnRHs stimulated lhβ messenger RNA (mRNA) expression but not fshβ mRNA expression, and only GnRH2 was able to increase maturation-inducing steroid (MIS) levels and possibly stimulate oocyte release. Furthermore, only GnRH2 was able to start the entire reproductive hormonal cascade and induce spawning., (© 2020 Wiley Periodicals LLC.)

The pituitary gonadotropins, Fsh (follicle-stimulating hormone) and Lh (luteinizing hormone), regulate testicular development and functions in all vertebrates. At the pituitary, different signaling systems regulate the synthesis and secretion of the gonadotropins, such as the hypothalamic neuropeptides GnRH (gonadotropin-releasing hormone) and GnIH (gonadotropin-inhibitory hormone). While GnRH exerts stimulatory roles, the actions of GnIH remain controversial for many teleost species. Therefore, the aim of this study was to evaluate the in vitro effects of chicken GnRH2 (cGnRH2) and zebrafish GnIH-3 (zGnIH-3) on the male gonadotropin and GnRH system expression using pituitary explants and brain slices from a neotropical species with economical and ecological relevance, Astyanax altiparanae. Our results showed that in males, cGnRH2 increased fshb and lhb mRNA levels in the pituitary explants. Interestingly, zGnIH-3 has no effect on basal gonadotropin expression, however zGnIH-3 decreased the cGnRH2-induced fshb and lhb transcripts in male pituitary explants. In the male brain slices, zGnIH-3 showed stimulatory effects, increasing gnrh2 mRNA levels. Overall, our results suggested that GnIH seems to have dual regulatory actions on gonadotropin and GnRH2 expression of A. altiparanae males. This study provided basic information on endocrine regulation of A. altiparanae reproduction, and the obtained results will expand our knowledge, improving the reproductive management of this economically important freshwater species., (Copyright © 2018 Elsevier Inc. All rights reserved.)

To better understand the endocrine control of reproduction in Characiformes and the reproductive dysfunctions that commonly occur in migratory fish of this order when kept in captivity, we chose Astyanax altiparanae, which has asynchronous ovarian development and multiple spawning events, as model species. From A. altiparanae pituitary total RNA, we cloned the full-length cDNAs coding for the follicle-stimulating hormone β subunit (fshb), the luteinizing hormone β subunit (lhb), and the common gonadotropin α subunit (gpha). All three sequences showed the highest degree of amino acid identity with other homologous sequences from Siluriformes and Cypriniformes. Real-time, quantitative PCR analysis showed that gpha, fshb and lhb mRNAs were restricted to the pituitary gland. In situ hybridization and immunofluorescence, using specific-developed and characterized polyclonal antibodies, revealed that both gonadotropin β subunits mRNAs/proteins are expressed by distinct populations of gonadotropic cells in the proximal pars distalis. No marked variations for lhb transcripts levels were detected during the reproductive cycle, and 17α,20β-dihydroxy-4-pregnen-3-one plasma levels were also constant, suggesting that the reproductive dysfunction seen in A. altiparanae females in captivity are probably due to a lack of increase of Lh synthesis during spawning season. In contrast, fshb transcripts changed significantly during the reproductive cycle, although estradiol-17β (E 2 ) levels remained constant during the experiment, possibly due to a differential regulation of E 2 synthesis. Taken together, these data demonstrate the putative involvement of gonadotropin signaling on the impairment of the reproductive function in a migratory species when kept in captivity. Future experimental studies must be carried to clarify this hypothesis. All these data open the possibility for further basic and applied studies related to reproduction in this fish model., (Copyright © 2016 Elsevier Inc. All rights reserved.)