Disturbing ion regulation and excretion in medaka (Oryzias melastigma) gills by microplastics: Insights from the gut-gill axis

Effect of polystyrene nanoplastics on the intestinal histopathology, oxidative stress, and microbiota of Acrossocheilus yunnanensis

Even though extensive research exists on the negative impact of nanoplastics on fish, their effect on the microbiota and intestinal health of freshwater fish remains unclear. This study investigated the impact of polystyrene nanoplastics (PS-NPs) on the microbiota, oxidative stress, and intestinal morphology of the Acrossocheilus yunnanensis (A. yunnanensis) freshwater fish species. The findings demonstrated that PS-NPs induced structural changes (e.g., epithelial rupture and microvilli damage) in the intestinal tissue of A. yunnanensis. Meanwhile, they increased the level of malondialdehyde (MDA) and the activity of superoxide dismutase (SOD) in the intestine, but did not significantly cause changes in the activities of catalase (CAT) and glutathione S-transferase (GST) enzymes. The microbiome results indicated that PS-NPs increased gut microbial community diversity and Proteobacteria abundance while decreasing the Fusobacteriota content. Furthermore, PS-NPs significantly improved multiple microbial functions such as amino acid and lipid transfer and metabolism, as well as energy generation and conversion. Overall, this study revealed that PS-NPs caused oxidative stress and microbiota dysbiosis in A. yunnanensis, possibly causing intestinal epithelial damage. This research elucidates the mechanism underlying PS-NP toxicity to freshwater fish and its subsequent impact.

Toxic effects of emerging pollutants on mucosal organs of teleost fish: A review focusing on mucosal microbiota, physical barrier and immune barrier

The urgency of emerging pollutants driven by human activities presents an increasing threat to the health of fish. The mucosal system, serving as a primary barrier against environmental pollutants, has emerged as a central focus in toxicological research. Alterations in the mucosal microbiota can impact health at both local and systemic levels. This review explores the toxic effects of emerging pollutants on the mucosal immunity of teleost fish, reflects on the reasons behind the limited focus on adaptive immunity studies, and highlights changes in microbial composition, gene expression, histology, and overall mucosal organ function. Furthermore, we summarize the mechanisms through which these pollutants disrupt the mucosal barriers of teleosts, emphasizing interactions between the mucosal microbiota, physical barriers, and immune defenses. The relevant methodologies and potential solutions to the current challenges have been summarized. While current research predominantly centers on the intestines and gills, further studies are needed to investigate the toxic effects of emerging pollutants on other mucosal organs and to elucidate how microbiota influence host health through neuro-immune communication. This review aims to provide a comprehensive overview of mucosal immunity, serving as a theoretical foundation for the assessment of related ecological risks.

Differential effects of foodborne and waterborne micro(nano)plastics exposure on fish liver metabolism and gut microbiota community

Micro(nano)plastics (MNPs) primarily enter fish through two routes: directly ingestion via their diets and respiratory filtration through their gills. However, the specific impacts of these two routes on liver metabolism remain largely unknown. Here, we investigated the gene expression profiles of the liver of Nile tilapia Oreochromis niloticus following equivalent doses of foodborne and waterborne MNPs exposure. While the liver phenotypes of O. niloticus showed minimal differences between the two exposure routes, significant variations were observed in gene response patterns. Using WGCNA, we identified the key gene networks and KEGG pathways associated with each exposure type. The primary transcription factors regulating gene expression changes were thrb for foodborne exposure and fosl2 for waterborne exposure. The stimulus of foodborne MNPs primarily induced metabolic disorders through circadian rhythm, whereas waterborne MNPs induced inflammatory responses to affect host metabolism. By integrating gene expression alterations with gut microbiota enrichment data, we further found that Firmicutes, Fusobacteriota, Proteobacteria, and Chloroflexi jointly regulated the expression of mapk13 during foodborne exposure, whereas the expression of the most leading genes in waterborne exposure was predominantly influenced by Firmicutes. Collectively, our study demonstrated a distinct pattern in microbiota-gene gut-liver axis in O. niloticus in response to foodborne and waterborne MNPs exposure.

In Vivo visualization of microplastic degradability and intestinal functional responses in a plastivore insect

The plastivore insect Tenebrio molitor demonstrates significant potential for the rapid biodegradation and bioremediation of micro(nano)plastics. However, real-time visualization of the digestive degradation and removal of microplastics (MPs) during intestinal transit, along with the associated in vivo intestinal functional responses, remains challenging. Here, we developed second near-infrared (NIR-II) window aggregated-induced emission (AIE) MPs of two sizes (29.8 μm and 299.5 μm, respectively) to enable real-time monitoring of MPs removal in T. molitor larvae, and quantified the degradation kinetics. Our findings revealed that small MPs were digested and passed through the intestine more rapidly compared to large MPs, in strong contrast with patterns observed in organisms lacking plastic-degrading capacity. Digestive removal was more pronounced in the posterior than in the anterior midgut. A NIR-II peroxynitrite probe (NIR-ONOO-) was synthesized to investigate the intestinal functional responses to MPs biodegradation. Generation of reactive nitrogen species (RNS) was extensive during feedstock digestion in the intestine. The larvae instinctively modulated the ONOO- levels and heterogeneously redistributed the ONOO- in response to MPs biodegradation, with a more pronounced effect observed in larvae fed large MPs. This work presents a robust trafficking technology for the dynamic and in vivo visualization of micro(nano)plastics removal and bioremediation in plastivore species.

Pulse exposure to microplastics depolarizes the goldfish gill: Interactive effects of DOC and differential degradation

Microplastics (MPs) are constantly degrading while moving through aquatic systems as a result of mechanical abrasion, thermal fluctuations, UV light, and chemical exposure. As such, fish may experience pulse exposures to differentially degraded plastics. This study addresses how pulse exposures, over the course of minutes, to differentially degraded microplastics alters a key ionoregulatory property of the goldfish gill. We used transepithelial potential (TEP) across the gills, a diffusion potential resulting from the differential permeability of cations versus anions, as a sensitive indicator of potential ionoregulatory effects. Virgin (non-degraded) MPs along with mechanically, UV, and thermally degraded plastics immediately depolarized the gills (less negative TEP), whereas chemically degraded MPs resulted in no change to TEP. To further explore the physicochemical interaction between the surface of the gill and MPs, combinations of MPs and a single source of dissolved organic carbon (DOC) were tested and revealed that the presence of DOC negated the effects of MPs at the gill regardless of whether DOC or MPs were introduced first. This study suggests that while MPs have the ability to cause ionoregulatory effects at the gill, the effects of ambient water quality, specifically the presence of DOC, are of greater influence.

Biotransport and toxic effects of micro- and nanoplastics in fish model and their potential risk to humans: A review

The growing body of scientific evidence suggests that micro- and nanoplastics (MPs/NPs) pose a significant threat to aquatic ecosystems and human health. These particles can enter organisms through ingestion, inhalation, dermal contact, and trophic transfer. Exposure can directly affect multiple organs and systems (respiratory, digestive, neurological, reproductive, urinary, cardiovascular) and activate extensive intracellular signaling, inducing cytotoxicity involving mechanisms such as membrane disruption, extracellular polymer degradation, reactive oxygen species (ROS) production, DNA damage, cellular pore blockage, lysosomal instability, and mitochondrial depolarization. This review focuses on current research examining the in vivo and in vitro toxic effects of MPs/NPs on aquatic organisms, particularly fish, in relation to particulate toxicity aspects (such as particle transport mechanisms and structural modifications). Meanwhile, from the perspectives of the food chain and environmental factors, it emphasizes the comprehensive threats of MPs/NPs to human health in terms of both direct and indirect toxicity. Additionally, future research needs and strategies are discussed to aid in mitigating the potential risks of particulate plastics as carriers of toxic trace elements to human health.

Metabolomics reveals the toxicity of polystyrene nanoplastics in the gills of Acrossocheilus yunnanensis

Although the ecotoxicity of polystyrene nanoplastics (PS-NP) to fish has been widely reported, their impact on the metabolic processes in fish gills and the underlying mechanisms remains unclear. Here, we investigated the effects of PS-NP on the morphology, oxidative stress, and metabolism of Acrossocheilus yunnanensis gills using conventional physicochemical indicators and metabolomics analysis. The results showed that PS-NP caused oxidative stress, and resulted in gill tissue lesions (e.g., proliferation and sloughing of gill epithelial cells). Metabolomics results showed that PS-NP exposure induced 75-164 differentially expressed metabolites (DEMs) in fish gills, and they were mainly related to lipid metabolism. DEMs induced by high concentration of PS-NP compared with low concentration of PS-NP were not only significantly enriched in glycerophospholipid metabolism, but also in sphingolipid metabolism, nucleic acid metabolism, and a variety of signaling pathways. In conclusion, the results of this work suggest that PS-NP cause disruption of phospholipid metabolism mainly by disrupting the integrity of gill tissue, which provides a new perspective for understanding the impact mechanism of PS-NP on fish gills. Given that fish play essential roles in maintaining ecological balance, the adverse effects of PS-NP on fish gills could ultimately disrupt the stability and health of the aquatic ecosystem.

Environmental behavior and toxic effects of micro(nano)plastics and engineered nanoparticles on marine organisms under ocean acidification: A review

Ocean acidification (OA) driven by human activities and climate change presents new challenges to marine ecosystems. At the same time, the risks posed by micro(nano)plastics (MNPs) and engineered nanoparticles (ENPs) to marine ecosystems are receiving increasing attention. Although previous studies have uncovered the environmental behavior and the toxic effects of MNPs and ENPs under OA, there is a lack of comprehensive literature reviews in this field. Therefore, this paper reviews how OA affects the environmental behavior of MNPs and ENPs, and summarizes the effects and the potential mechanisms of their co-exposure on marine organisms. The review indicates that OA changes the marine chemical environment, thereby altering the behavior of MNPs and ENPs. These changes affect their bioavailability and lead to co-exposure effects. This impacts marine organisms' energy metabolism, growth and development, antioxidant systems, reproduction and immunity. The potential mechanisms involved the regulation of signaling pathways, abnormalities in energy metabolism, energy allocation, oxidative stress, decreased enzyme activity, and disruptions in immune and reproductive functions. Finally, based on the limitations of existing research, actual environment and hot issues, we have outlined future research needs and identified key priorities and directions for further investigation. This review deepens our understanding of the potential effects of MNPs and ENPs on marine organisms under OA, while also aiming to promote further research and development in related fields.

Study on the physiological responses and tolerance mechanisms to subchronic carbonate alkalinity exposure in the gills of Paramisgurnus dabryanus

Given the reduction of freshwater resources, saline-alkaline aquaculture has emerged as an effective approach to expand the fishery's accessible space. High carbonate alkalinity (CA) is a major stressor for aquatic organisms in saline-alkaline environments. Paramisgurnus dabryanus is a potential species for culture in saline-alkaline water, making it an ideal model for investigating the physiological responses and tolerance mechanisms to CA exposure in freshwater fishes. In the current study, P. dabryanus were exposed to 15 and 30 mmol/L NaHCO3, combining blood biochemical, gill histological, transcriptomic, and metabolomic methods for conjoint analysis of response mechanisms. After 28-d exposure, the gill ventilation frequency of P. dabryanus decreased significantly, gill lamellae twisted and atrophied, and gill filament epithelial cells proliferated, potentially limiting gas exchange, whereas the accessory air-breathing frequency increased significantly, possibly for greater oxygen uptake. Serum osmolality and blood pH remained relatively steady, while serum ammonia levels rose significantly. A total of 3718 differentially expressed genes (DEGs) and 205 differential metabolites (DMs) were identified between the control group and 30 mmol/L NaHCO3 group, involved in ion transport (Na+/K+-ATPase, V-type ATPase, carbonic anhydrase, and ABC transporters), ammonia transport (Rh glycoproteins and Aquaporins), amino acid metabolism, carbohydrate metabolism, and fatty acid metabolism. Furthermore, DEGs were significantly associated with cell-cell/ extracellular matrix interaction and protein synthesis. An integrated multi-omics analysis revealed the activation of carbon metabolism and TCA cycle. These results indicate that in response to CA exposure, P. dabryanus may facilitate carrier-mediated ion and ammonia transport to maintain the internal osmotic equilibrium and lessen the deleterious effects of blocked ammonia excretion. Meanwhile, amino acid metabolism and protein synthesis are disturbed, P. dabryanus can modulate carbohydrate catabolism to maintain energy homeostasis. The above findings provide novel insights into saline-alkaline adaptation in freshwater fishes, paving the way for future research and development of saline-alkaline-tolerant Cobitidae strains.

Contrasting the distribution kinetics of microplastics and nanoplastics in medaka following exposure and depuration

Direct ingestion of micro/nanoplastics (MNPs) results in significant accumulation in gastrointestinal (GI) tract of fish. The breathing process of fish makes MNPs easily retained in their gills. However, the uptake of MNPs in other fish organs remains largely unknown, let alone their kinetic processes. Herein, microplastics (MPs) and nanoplastics (NPs) in vivo imaging and precise quantification in various tissues (GI tract, gill, liver, brain, eye, and skin) of seawater (SW)- and freshwater (FW)- acclimated medaka Oryzias melastigma were achieved at an environmentally relevant concentration. Subsequently, the distribution kinetics of MNPs was investigated over a 96-h uptake and 48-h depuration period. MNPs were quickly and mostly captured in GI tract and gill of O. melastigma, and then transferred to liver and brain likely via blood circulation. Such transport was more efficient for NPs as compared to MPs, as evidenced by the consistently higher bioconcentration factors in both SW and FW conditions. The detection of MNPs in eye and skin of O. melastigma was more of an adsorption process, although the specific mechanisms of adsorption and absorption process can hardly be clearly differentiated. This study presented distribution kinetics of MNPs in O. melastigma and highlighted their possible transportation among tissues.

Norfloxacin affects inorganic nitrogen compound transformation in tailwater containing Corbicula fluminea

The Asian clam, Corbicula fluminea, commonly used in engineered wetlands receiving tailwater, affects nitrogen compound transformation in water. This study investigates how a commonly observed antibiotic in tailwater, norfloxacin, impact nitrogen compound transformation in tailwater containing C. fluminea. The clam was exposed to artificial tailwater with norfloxacin (0, 0.2, 20, and 2000 μg/L) for 15 days. Water properties, C. fluminea ecotoxicity responses, microorganism composition and nitrification- or denitrification-related enzyme activities were measured. Results revealed norfloxacin-induced increases and reductions in tailwater NH4+ and NO2- concentrations, respectively, along with antioxidant system inhibition, organ histopathological damage and disruption of water filtering and digestion system. Microorganism composition, especially biodiversity indices, varied with medium (clam organs and exposure water) and norfloxacin concentrations. Norfloxacin reduced NO2- content by lowering the ratio between microbial nitrifying enzyme (decreased hydroxylamine oxidoreductase and nitrite oxidoreductase activity) and denitrifying enzyme (increased nitrate reductase and nitrite reductase activity) in tailwater. Elevated NH4+ content resulted from upregulated ammonification and inhibited nitrification of microorganisms in tailwater, as well as increased ammonia emission from C. fluminea due to organ damage and metabolic disruption of the digestion system. Overall, this study offers insights into using benthic organisms to treat tailwater with antibiotic residues, especially regarding nitrogen treatment.

The effects of microplastics on ionoregulatory processes in the gills of freshwater fish and invertebrates: A prospective review

From review of the very few topical studies to date, we conclude that while effects are variable, microplastics can induce direct ionoregulatory disturbances in freshwater fish and invertebrates. However, the intensity depends on microplastic type, size, concentration, and exposure regime. More numerous are studies where indirect inferences about possible ionoregulatory effects can be drawn; these indicate increased mucus production, altered breathing, histopathological effects on gill structure, oxidative stress, and alterations in molecular pathways. All of these could have negative effects on ionoregulatory homeostasis. However, previous research has suffered from a lack of standardized reporting of microplastic characteristics and exposure conditions. Often overlooked is the fact that microplastics are dynamic contaminants, changing over time through degradation and fragmentation and subsequently exhibiting altered surface chemistry, notably an increased presence and diversity of functional groups. The same functional groups characterized on microplastics are also present in dissolved organic matter, often termed dissolved organic carbon (DOC), a class of substances for which we have a far greater understanding of their ionoregulatory actions. We highlight instances in which the effects of microplastic exposure resemble those of DOC exposure. We propose that in future microplastic investigations, in vivo techniques that have proven useful in understanding the ionoregulatory effects of DOC should be used including measurements of transepithelial potential, net and unidirectional radio-isotopic ion flux rates, and concentration kinetic analyses of uptake transport. More sophisticated in vitro approaches using cultured gill epithelia, Ussing chamber experiments on gill surrogate membranes, and scanning ion selective electrode techniques (SIET) may also prove useful. Finally, in future studies we advocate for minimum reporting requirements of microplastic properties and experimental conditions to help advance this important emerging field.

Single-Cell RNA Sequencing Profiling Cellular Heterogeneity and Specific Responses of Fish Gills to Microplastics and Nanoplastics

Fish gills are highly sensitive organs for microplastic (MP) and nanoplastic (NP) invasions, but the cellular heterogeneity of fish gills to MPs and NPs remains largely unknown. We employed single-cell RNA sequencing to investigate the responses of individual cell populations in tilapia Oreochromis niloticus gills to MP and NP exposure at an environmentally relevant concentration. Based on the detected differentially expressed gene (DEG) numbers, the most affected immune cells by MP exposure were macrophages, while the stimulus of NPs primarily targeted T cells. In response to MPs and NPs, H+-ATPase-rich cells exhibited distinct changes as compared with Na+/K+-ATPase-rich cells and pavement cells. Fibroblasts were identified as a potential sensitive cell-type biomarker for MP interaction with O. niloticus gills, as evidenced by the largely reduced cell counts and the mostly detected DEGs among the 12 identified cell populations. The most MP-sensitive fibroblast subpopulation in O. niloticus gills was lipofibroblasts. Cell-cell communications between fibroblasts and H+-ATPase-rich cells, neurons, macrophages, neuroepithelial cells, and Na+/K+-ATPase-rich cells in O. niloticus gills were significantly inhibited by MP exposure. Collectively, our study demonstrated the cellular heterogeneity of O. niloticus gills to MPs and NPs and provided sensitive markers for their toxicological mechanisms at single-cell resolution.

Microplastics and nanoplastics induced differential respiratory damages in tilapia fish Oreochromis niloticus

With the increasing micro(nano)plastics (MNPs) pollution in aquatic environments, fish respiration is encountering a huge threat. Herein, polystyrene (PS) MNPs with three sizes (80 nm, 2 µm, and 20 µm) were exposed to tilapia Oreochromis niloticus at an environmentally relevant concentration of 100 μg/L for 28 days and their impacts on respiratory function were investigated. Based on the results of oxygen consumption and histological analysis, all the three treatments could induce respiratory damages and such impacts were more severe for the 2 µm and 20 µm treatments than for the 80 nm treatment. These results were explained by the more significant upregulation of egln3 and nadk, and the downregulation of isocitrate. Transcriptomics and metabolomics further revealed that TCA cycle played a key role in respiratory dysfunction induced by micro-sized PS particles, and cytokine and chemokine related functions were simultaneously enriched. Although nano-sized PS particles had the potential to penetrate the respiratory epithelium and reached the internal structure of the O. niloticus gills, they were easily expelled through the blood circulation. Our results highlighted the serious threat of MNPs to fish respiration and provided insights into the differential toxicological mechanisms between micro-sized and nano-sized particles, thus assisting in ecological risk assessments.

Fish Physiologically Based Toxicokinetic Modeling Approach for In Vitro-In Vivo and Cross-Species Extrapolation of Endocrine-Disrupting Chemicals in Risk Assessment

High-throughput in vitro assays combined with in vitro-in vivo extrapolation (IVIVE) leverage in vitro responses to predict the corresponding in vivo exposures and thresholds of concern. The integrated approach is also expected to offer the potential for efficient tools to provide estimates of chemical toxicity to various wildlife species instead of animal testing. However, developing fish physiologically based toxicokinetic (PBTK) models for IVIVE in ecological applications is challenging, especially for plausible estimation of an internal effective dose, such as fish equivalent concentration (FEC). Here, a fish PBTK model linked with the IVIVE approach was established, with parameter optimization of chemical unbound fraction, pH-dependent ionization and hepatic clearance, and integration of temperature effect and growth dilution. The fish PBTK-IVIVE approach provides not only a more precise estimation of tissue-specific concentrations but also a reasonable approximation of FEC targeting the estrogenic potency of endocrine-disrupting chemicals. Both predictions were compared with in vivo data and were accurate for most indissociable/dissociable chemicals. Furthermore, the model can help determine cross-species variability and sensitivity among the five fish species. Using the available IVIVE-derived FEC with target pathways is helpful to develop predicted no-effect concentration for chemicals with similar mode of action and support screening-level ecological risk assessment.

Impacts of Nile Tilapia (Oreochromis niloticus) exposed to microplastics in bioflocs system

Microplastics (MPs) are abundant in aquaculture water, including in bioflocs aquaculture systems. Compared with other aquaculture systems, biofloc technology systems have the richest microbes and are beneficial to cultivated organisms. Therefore, this study provides a comprehensive assessment of the potential effects of MPs on aquaculture organisms in bioflocs systems. Here, Nile Tilapia (Oreochromis niloticus) were exposed to MPs (polystyrene; 32-40 μm diameter) with 0, 80 items/L (30 μg/L), and 800 items/L (300 μg/L) for 28 days in a bioflocs aquaculture system. The results showed that the MPs generally had no apparent effect on water quality, tilapia growth, or digestive enzyme activity. However, MPs accumulated the most in the liver (5.65 ± 0.74 μg/mg) and significantly increased the hepato-somatic index of tilapia and reduced the crude protein and lipid of tilapia muscle (p < 0.05). The levels of the antioxidant enzymes catalase and glutathione S-transferase increased significantly in response to MPs (p < 0.05). In contrast, MPs did not affect the content of glutathione, glutathione peroxidase, oxidized glutathione, and malondialdehyde, or the enzyme activity of Na+/K+-ATPase. Moreover, using an improved integrated biomarker response index, growth performance was found to be less responsive to MPs than to oxidative stress and digestive activity. Exposure to MPs did not significantly influence the microbial communities of the bioflocs and tilapia guts (p < 0.05). These results suggest that MPs barely affected tilapia in the bioflocs system. This study contributes to the evaluation of the ecological risk of MPs in aquaculture systems and a better understanding of the integrated response of cultivated vertebrates to MPs in biofloc technology systems.

Near-Infrared-II In Vivo Visualization and Quantitative Tracking of Micro/Nanoplastics in Fish

As emerging contaminants, micro/nanoplastics (MNPs) are widely present in aquatic environments and are often ingested by aquatic organisms. However, the in vivo trafficking and fate of MNPs remain largely unknown. Here, we developed near-infrared (NIR) aggregated-induced emission (AIE) fluorophore-labeled microplastics (2 μm) and nanoplastics (100 nm) as models of MNPs. This model was based on the NIR-AIE technique with strong emission at the second near-infrared (NIR-IIII) window, which overcomes the interference of autofluorescence and observation artifacts in the detection of commercial fluorescent-labeled particles. Due to its deep tissue penetration and noninvasiveness, the dynamic process of accumulation and transport of MNPs in individuals can be tracked with NIR imaging. We then directly visualized and quantified the uptake and depuration processes of MPs and NPs in zebrafish. The results showed that the MPs and NPs were mainly accumulated in the fish gut, and the distribution was heterogeneous. MPs tended to accumulate more in the fore and mid areas of the gut compared with NPs. Besides, both MPs and NPs could accumulate in large quantities locally in the gut and might cause intestinal obstruction. MNPs accumulated slowly during the initial exposure followed by rapid and sustained accumulation in gut. Based on these kinetic accumulation and depuration, we developed a refined toxicokinetic (TK) model to describe the dynamic changes in the uptake and depuration of MNPs. Overall, this study proposed a MNP model based on the NIR-AIE technique, which provided a reliable tracer technology for the visualization, tracking and quantification of MNPs in vivo.

Physiological and immune profiling of tilapia Oreochromis niloticus gills by high-throughput single-cell transcriptome sequencing

The physiological and immune functions of fish gills are largely recognized, but their following functional heterogeneity at the single cell scale has been rarely reported. Here, we performed single cell RNA sequencing (scRNA-seq) on the gills of tilapia fish Oreochromis niloticus. We identified a total of 12 cell populations and analyzed their functional heterogeneity. To investigate the physiological function of O. niloticus gills, expression patterns of genes encoding ion transporters were selected from the identified H+-ATPase-rich cells (HR cells), Na+/K+-ATPase-rich cells (NaR cells), and pavement cells. Specific enrichment of ca4a, slc9a1a, and LOC100692482 in the HR cells of O. niloticus gills explained their functions in acid-base regulation. Genes encoding Ca2+ transporters, including atp2b1, LOC100696627, and LOC 100706765, were specifically expressed in the NaR cells. Pavement cells were presumably the main sites responsible for ammonia and urea transports in O. niloticus gills with specific enrichment of Rhbg and LOC100693008, respectively. The expression patterns of the four immune cell subtypes varied greatly, with B cells being enriched with the most immune-related GO terms. KEGG enrichment analysis showed that MAPK signaling pathway was the most enriched pathway among the four types of immune cells in O. niloticus gills. Our results are important in understanding the physiological and immune responses of fish gills at the cellular resolution.

Occurrence and accumulation of microplastics in commercial fish in the coastal waters of the Lvsi fishing ground in China

In recent years, there has been an exponential increase in the research popularity of microplastics (MPs) in offshore marine environments. However, there is still a gap in the research on the accumulation of MPs in different tissues of aquatic organisms and the trophic transfer of MPs between aquatic organisms. The common occurrence of MPs in the gills and guts of 11 species of commercial fishes was examined in the coastal waters of the Lvsi fishing ground (LSFG). The obtained results showed that >85 % of MPs existed in the gills and guts of these fish, and the abundance was 2.39 ± 1.38 pieces/fish and 2.56 ± 1.42 pieces/fish, respectively. Fibrous and blue are the most common colors and shapes of MPs, and PET is the main polymer type. At the species level, the abundance of MPs in the gills and guts of a few fishes (e.g., Larimichthys polyactis, Setipinna tenuifilis, Collichthys lucidus) decreased with increasing body length and body weight (P < 0.05). At the community level, this situation was not significant (P > 0.05). With increasing trophic level (TL), MPs tended to decrease in the gills (trophic magnification factor, TMF = 0.86) but did not significantly vary in the gut. We believe that MPs are multidimensional pollutants, and their accumulation in tissues/organs of organisms has not been accurately and qualitatively determined. To establish the relationship of MP transport and trophic transfer among water, sediments and organisms, we suggest that more efforts should be made to investigate MPs in aquatic organisms in the coastal waters of LSFG and to increase the examination of MPs in the water column and sediments. This study will help us improve our understanding of MPs pollution, and provide a good reference and basis for the management, monitoring and implementation of pollutants in marine organism of coastal water.

Conventional Anthelmintic Concentration of Deltamethrin Immersion Disorder in the Gill Immune Responses of Crucian Carp

Current treatment strategies for parasitic infectious diseases in crucian carp primarily rely on chemotherapy. As a commonly used antiparasitic agent, deltamethrin (DEL) may have the potential adverse effects on external mucosa of fish such as gills. In this study, 180 healthy juvenile crucian carp (Carassius auratus) (average weight: 8.8 ± 1.0 g) were randomly divided into three groups for 28 days, which were immersed in 0 μg/L, 0.3 μg/L, and 0.6 μg/L of DEL, respectively. The results of histological analysis revealed that severe hyperplasia in the secondary lamellae of gills was observed, and the number of goblet (mucus-secreting) cells increased significantly after DEL immersion. TUNEL staining indicated that the number of apoptotic cells increased in crucian carp gill. At the molecular level, the mRNA expression analysis revealed significant upregulation of apoptosis (caspase 3, caspase 8, and bax), autophagy (atg5 and beclin-1), and immune response (lzm, muc5, il-6, il-8, il-10, tnfα, ifnγ, tgfβ, tlr4, myd88, and nf-kb), whereas tight junction-related genes (occludin and claudin12) were downregulated after DEL immersion, suggesting that DEL immersion altered innate immunity responses and promoted mucus secretion. Moreover, tandem mass tag (TMT)-based proteomics revealed that a total of 428 differentially expressed proteins (DEPs) contained 341 upregulated DEPs and 87 downregulated DEPs with function annotation were identified between the control and DEL groups. Functional analyses revealed that the DEPs were enriched in apoptotic process, phagosome, and lysosome pathways. Additionally, DEL immersion also drove gill microbiota to dysbiosis and an increase in potentially harmful bacteria such as Flavobacterium. Overall, this study showed that DEL elicited shifts in the immune response and changes in the surface microbiota of fish. These results provide new perspectives on the conventional anthelmintic concentration of DEL immersion disorder of the gill immune microenvironment in crucian carp and theoretical support for future optimization of their practical application.

First report on the toxicity of SARS-CoV-2, alone and in combination with polyethylene microplastics in neotropical fish

The COVID-19 pandemic has caused unprecedented negative impacts in the modern era, including economic, social, and public health losses. On the other hand, the potential effects that the input of SARS-CoV-2 in the aquatic environment from sewage may represent on non-target organisms are not well known. In addition, it is not yet known whether the association of SARS-CoV-2 with other pollutants, such as microplastics (MPs), may further impact the aquatic biota. Thus, we aimed to evaluate the possible ecotoxicological effects of exposure of male adults Poecilia reticulata, for 15 days, to inactivated SARS-CoV-2 (0.742 pg/L; isolated SARS.CoV2/SP02.2020.HIAE.Br) and polyethylene MP (PE MPs) (7.1 × 10⁴ particles/L), alone and in combination, from multiple biomarkers. Our data suggest that exposure to SARS-CoV-2 induced behavioral changes (in the open field test), nephrotoxic effect (inferred by the increase in creatinine), hepatotoxic effect (inferred by the increase in bilirubin production), imbalance in the homeostasis of Fe, Ca, and Mg, as well as an anticholinesterase effect in the animals [marked by the reduction of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activity]. On the other hand, exposure to PE MPs induced a genotoxic effect (assessed by the comet assay), as well as an increase in enzyme activity alpha-amylase, alkaline phosphatase, and carboxylesterases. However, we did not show synergistic, antagonistic, or additive effects caused by the combined exposure of P. reticulata to SARS-CoV-2 and PE MPs. Principal component analysis (PCA) and values from the "Integrated Biomarker Response" index indicate that exposure to SARS-CoV-2 was determinant for a more prominent effect in the evaluated animals. Therefore, our study sheds light on the ecotoxicity of the new coronavirus in non-target organisms and ratifies the need for more attention to the impacts of COVID-19 on aquatic biota.