Organ-specific responses to total ammonia nitrogen stress on juvenile grass carp (Ctenopharyngodon idellus)

Evaluation of the acute toxic effects of ammonia on juvenile ussuri cisco (Coregonus ussuriensis) based on histopathology, antioxidant enzyme activity, immune response and the integrated biomarker response

Aquaculture intensification system is challenged by high ammonia concentrations, which can affect fish physiology. In the present study, we assessed the effects of ammonia on ussuri cisco based on histopathology, antioxidant enzyme activity, immune response, and integrated biomarker responses. After exposure to 60.0 mg/L ammonia, liver vacuolization, bruising, nucleolysis, cell swelling, cell rupture, and structural irregularities were observed. It was found that the degree of liver damage increased with the duration of stress and was most severe at 72 h. During ammonia stress, the serum levels of SOD, CAT, MDA and T-AOC in the treatment groups showed a tendency to increase and then decrease. In addition, the serum activities of GOT, GPT and AKP were significantly higher in the treatment group than in the control group after ammonia exposure. We also evaluated the immune regulatory mechanisms of the NF-κB pathway and showed that immune-related genes (TNF-α, TAK1, NFKBIA, IKBKB, P50, P65, IL-8, IL-1β and A20) were differentially elevated during the exposure period, especially TNF-α, IL-8, IL-1β and A20 which were all highly expressed. CAT, GPT, AKP and SOD were identified as representative markers of biotoxic effects. This will help to more accurately estimate the ecological risk of environmental ammonia to fish populations.

IR-based device to acquire real-time online heart ECG signals of fish (Cyprinus carpio) to evaluate the water quality

Water quality monitoring is a challenging task due to continuous pollution. The rapid development of engineering technologies has paved the way for the development of efficient and convenient computer-based online continuous water-quality assessment techniques. Techniques based on biological-responses are gaining attention, worldwide. Different biosensors have been developed in recent years to monitor real-time biological responses to evaluate water-quality. The survival and function of various organs of the organism depends on the cardiac system. Alterations in the cardiac system could signify the occurrence/initiation of stress in the organism. We developed a real-time online cardiac function assessment system-OCFAS to acquire fish ECG-signals. We obtained P-wave, R-wave, T-wave, PR-intervals, QT-intervals and QRS-complex continuously, which did not affect the normal activities of carp. We exposed Cyprinus carpio to different concentrations (National Environmental Quality Standards) of ammonia for 48 h. Our OCFAS has precisely acquired the required ECG-signals. A real-time dataset reveals sensitivity to ammonia in carp ECG-indexes. Compared with the control group the P-wave, R-wave and T-wave were weaker in ammonia-treated groups. In contrast, the PR-intervals, QT-intervals and QRS-complex were prolonged in the ammonia-treatment groups. The self-organizing map signifies that the PR-intervals, the QRS-complex and the QT-intervals are consistent with environmental stress. Linear regression analysis also quantitatively signifies that the PR interval has the highest R2 value and the lowest SSE-value, followed by the QRS complex and the QT interval. A concentration-related effect was observed in the ammonia treated groups. The integrated biomarker response (IBRv2) index was used to determine the overall stress of ammonia on carp heart ECG-indexes. IBRv2 also supports the real-time response of carp to ammonia stress. Ammonia levels in the aquaculture and water environment require special attention to avoid its adverse effects on the health of aquatic biota. Our study emphasizes the importance of online real-time fish ECG for water-quality assessment.

Release of dissolved organic matter from wetland plants and its interaction with polycyclic aromatic hydrocarbons

Dissolved organic matter (DOM) derived from wetland plants played a critical role in CWs pollutant migration. This study investigated the character and release pattern of DOM derived from two wetland plants, Phragmites australis and Cladophora sp., and the interaction between DOM with phenanthrene (PHE), benzo(a)pyrene (Bap), and benzo [k]fluoranthene (BkF) under different physical conditions were also studied using spectroscopic techniques. DOM release was related to plant species and withering stage. Humic acid (HA)-like fractions (C3 and C5) were dominated in P. australis (52%) and completely withered Cladophora sp. groups (55%), while protein-like fractions (C1 and C2) dominated in early withered Cladophora sp. groups (52%). Due to the cell and tissue structure difference among plants and their withering stage, DOM derived from early withered P. australis revealed a two-stage slow-fast phase, while other groups were linearly released (R2 0.87207-0.97091). A strong correlation existed between HA-like fractions and water quality index, reflecting the critical influence of plant decay in CWs operation performance. The analysis with Stern-Volmer equation indicated that plant-based DOM interacted with PAHs to form ground state complexes with possible involvement of π-π interaction, hydrogen bonding and cation bridging effect. Aromatic, molecular weight, and hydrophilicity of both DOM and PAHs affected their binding with the interaction capability in the order of BKF > Bap > PHE and C3 > C5 > C2 > C1 > C4. Besides, alkaline environment and high DO condition was highly unsuitable for the combination. Scientific management and appropriate operating condition were important in optimizing operation performance and controlling pollutant migration in CWs.

Cooperative adaptation strategies of different tissues in blunt snout bream (Megalobrama amblycephala) juvenile to acute ammonia nitrogen stress

Ammonia-nitrogen is a common stress factor for aquatic organisms in their habitation environment, which is enriched in water due to high-density farming and environmental pollution. Ammonia nitrogen can enter fish body through gill, epidermis, digestive tract, and other tissues, causing fish ammonia poisoning. In the present study, juvenile blunt snout bream (average weight, 45 ± 5 g) were exposed to high concentrations of ammonia-nitrogen stress (25.0 ± 0.5 mg/L) for six different treatment times (0, 3, 6, 12, 24, 48, and 72 h); the tissue ultrastructure, mRNA levels of antioxidation system, and apoptosis patterns were studied. The antioxidant systems of malondialdehyde (MDA), catalase (CAT), acid phosphatase (ACP), and reduced glutathione (GSH) in various tissues were highly transcripted at 6 or 12 h (hpt) after treatment under high ammonia-nitrogen, which may play a role in preventing cells from being attacked by highly toxic reactive oxygen species (ROS). After 24 hpt, the antioxidant capacity threshold is breached, followed by the decline of antioxidant enzyme activity. Thus, with the prolonging of high ammonia-nitrogen processing time, ammonia-nitrogen stress caused irreversible damage of organs (gill, liver, and kidney). Furthermore, the expression of caspase-3 apoptotic pathway was highly induced in different tissues, implying the apoptotic system is activated, which causes extensive cell apoptosis in different tissues as shown using TUNEL analysis. In conclusion, we observed that, in response to acute ammonia-nitrogen stress, blunt snout bream enhances antioxidant capacity and cell apoptosis.

The IL17 signaling pathway: A potential signaling pathway mediating gill hyperplasia and inflammation under ammonia nitrogen stress was identified by multi-omics analysis

Ammonia nitrogen is extremely toxic to aquatic animals, and is also the most common pollutant in the aquatic environment. In order to investigate the effect of high concentration of ambient ammonia nitrogen on fish gills, two groups, including a high ammonia group (T group: TAN = 2.5 mg/L, 10 % 96 h LC50) and a control group (Z group: total ammonia nitrogen (TAN) = 0 mg/L) were set up in this study. The effects of chronic ammonia stress on the gills of Pelteobagrus fulvidraco were investigated by histopathological, enzymatic, transcriptomic and proteomic analyses after 28 d of stress at different ammonia nitrogen concentrations. Histopathological observations revealed significant inflammatory cell infiltration, necrotic and abscission at the base of the gill filaments, and massive proliferation of cells at the base of the gill lamellae. Ammonia nitrogen stress led to increased reactive oxygen species (ROS) content and decreased catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-PX) activities in gills, indicating significant oxidative stress in gills. And further transcriptomic analysis revealed that 807 differential expression genes (DEGs) were generated in the gills, of which 587 DEGs were up-regulated and 220 DEGs were down-regulated. In addition, proteomics analysis identified 1073 differential expression proteins (DEPs) in gills, including 983 up- and 90 down-regulated DEPs. Pathway enrichment analysis of the DEGs and DEPs revealed that multiple inflammation-related signaling pathways were activated in the gill, including the significantly enriched IL17 signaling pathway. This suggests that IL17 signaling pathway might have a significant impact during signaling transduction. Further analysis of network regulation by mapping DEGs and DEPs to KEGG pathway revealed that IL17 signaling pathway mediated inflammation and cell proliferation in gills under ammonia stress. The results of this study provided new insights into the response of fish gills to ammonia nitrogen stress, and the IL17 signaling pathway may be a potential therapeutic target for reducing ammonia nitrogen gill toxicity.

High dissolved oxygen exacerbates ammonia toxicity with sex-dependent manner in zebrafish

Ammonia nitrogen is one of the important environmental factors, and causes negative effects for fish health in ecosystem and aquaculture. The toxic effects and mechanisms of ammonia in fish deserve further investigation. In the present study, we exposed female and male zebrafish (Danio rerio) to ammonia (50 mg/L NH₄Cl) with oxygenated (7.5-7.8 mg/L) or non‑oxygenated (3.8-4.5 mg/L) water, to identify the combined effects of dissolved oxygen and ammonia on fish with gender difference. The results showed that oxygenated ammonia exposure increased fish mortality, gill secondary lamellas damage and gill tissue spaces, gene expressions of proinflammatory interleukin 1 beta (il-1β) and apoptotic caspase8 as compared with non‑oxygenated ammonia. Besides, oxygenated ammonia elevated plasma ammonia contents, and decreased the discharge of body ammonia through gills by depressing the enzyme activity of Na⁺/K⁺-ATPase. Notably, when zebrafish were subjected to ammonia stress, more severe mortality, gill damage and tissue inflammatory response were observed in males than females. This is the first study to clarify the gender-dependent impacts of ammonia toxicity, and the adverse effects of oxygenation on ammonia resistance in zebrafish.

Ammonium induces oxidative stress, endoplasmic reticulum stress, and apoptosis of hepatocytes in the liver cell line of grass carp (Ctenopharyngodon idella)

Under unfavorable agricultural conditions, ammonia toxicity has become a major problem, resulting in a large number of deaths. Ammonia has been shown to be hepatotoxic. Research has also shown that ammonia can damage the livers of carp, but the mechanism is unclear. In this study, normal grass carp hepatocytes (L8824) were exposed to ammonia water to investigate the effect of ammonia on hepatocyte injury and apoptosis and its mechanism. The results showed that ammonia (50 mM) reduced the viability of L8824 cells and increased glutamic pyruvic transaminase (ALT, up 144.95%, P < 0.01) and glutamic oxalacetic transaminase (AST, up 65.27%, P < 0.01). Furthermore, exposure to ammonia induced oxidative stress and endoplasmic reticulum (ER) stress in L8824 cells. Elevated levels of reactive oxygen species (ROS) and malondialdehyde (MDA) and decreased mitochondrial membrane potential indicated that L8824 cells suffered oxidative damage. Endoplasmic reticulum stress manifests as increased expression degrees of PERK, ATF4, and IRE-1α. These results confirmed the toxicity of ammonia to hepatocytes. In addition, the rate of apoptosis in L8824 cells was increased 69.66% after exposure to ammonia (50 mM, P < 0.01). However, pretreatment of L8824 cells with ER stress inhibitor 2-APB reduced ammonia-induced calcium release (26.50%, P < 0.01) in endoplasmic reticulum. These results indicate that ammonia can exert toxic effects on L8824 cells through inducing endoplasmic reticulum stress and oxidative stress, resulting in apoptosis in L8824 cells.

Responses of Micropterus salmoides under Ammonia Stress and the Effects of a Potential Ammonia Antidote

Ammonia is a common environmental limiting factor in aquaculture. To investigate the effects of ammonia stress and explore the protective effect of N-carbamylglutamate (NCG) on Micropterus salmoides (M. salmoides), tissue sections and parameters related to oxidative stress and the inflammatory response in M. salmoides were carried out during the ammonia stress test and feeding test. The results demonstrated that the LC50 for 24 h, 48 h, 72 h, and 96 h under ammonia stress in M. salmoides were 25.78 mg/L, 24.40 mg/L, 21.90 mg/L, and 19.61 mg/L, respectively. Under ammonia stress, the structures of the tissues were damaged, and the GSH content decreased, while the MDA content increased with the increase in stress time and ammonia concentration. The NO content fluctuated significantly after the ammonia nitrogen stress. In the 15-day feeding test, with the increased NCG addition amount and feeding time, the GSH content increased while the MDA and NO contents decreased gradually in the NCG addition groups (NL group: 150 mg/kg; NM group: 450 mg/kg; NH group: 750 mg/kg) when compared with their control group (CK group: 0 mg/kg). In the ammonia toxicology test after feeding, the damage to each tissue was alleviated in the NL, NM, and NH groups, and the contents of GSH, MDA, and NO in most tissues of the NH group were significantly different from those in the CK group. The results suggested that ammonia stress caused tissue damage in M. salmoides, provoking oxidative stress and inflammatory response. The addition of NCG to the feed enhances the anti-ammonia ability of M. salmoides. Moreover, the gill and liver might be the target organs of ammonia toxicity, and the brain and kidney might be the primary sites where NCG exerts its effects. Our findings could help us to find feasible ways to solve the existing problem of environmental stress in M. salmoides culture.

Effects of partial replacement of dietary flour meal with seaweed polysaccharides on the resistance to ammonia stress in the intestine of hybrid snakehead (Channa maculatus ♀ × Channa argus ♂)

The purpose of this study was to evaluate the effects of partial replacement of dietary flour meal with seaweed polysaccharides on survival rate, histology, intestinal oxidative stress levels, and expression of immune-related genes in hybrid snakeheads under acute ammonia stress. Four experimental diets were set: (C) basal diet with 0% of seaweed polysaccharides as the control group, (MR) basal diet with 10% of seaweed polysaccharides, (HR) basal diet with 15% of seaweed polysaccharides, (HF) basal diet with 10% of fish oil. After 60 days of feeding, fish fed with the diet of C group were sampled as the control group, and other fish were exposed to ammonia nitrogen for 48 h. Two concentrations of total ammonia nitrogen (TAN) were used in this study: 120 mg/L TAN (low concentration exposure group), and 1200 mg/L TAN (high concentration exposure group). After exposure to ammonia nitrogen for 48 h, fish were sampled. The results indicated that adding seaweed polysaccharides to the diet could improve the survival rate of hybrid snakeheads under high concentration of ammonia stress. Histopathological analysis demonstrated multiple abnormalities in gills and intestines after exposure to two concentrations of TAN. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and lactate dehydrogenase (LDH) were all increased in the MR group under two concentrations of TAN stress. The mRNA abundance of immune-related genes in fish intestinal tissues was significantly induced or inhibited. These results suggested that partial replacement of dietary flour meal with seaweed polysaccharides improved the ability of hybrid snakeheads to resist ammonia stress.

New Insights into the Relationships between Bacterial Dynamics and Water Quality of Aquaculture Systems Supplemented with Carbon Source and Biofilm Substratum

Aquaculture is crucial for achieving the FAO’s goal of a world without hunger and malnutrition. Recently, biofilm substratum has been proposed as an effective means to control waste pollution caused by excessive nutrient inputs from aquaculture, but key bacterial communities involved in the remediation remain unclear. Here we reported a freshwater mesocosm study where the addition of biofilm substrata with external carbon effectively controlled the total ammonia nitrogen and improved fish growth. 16S rRNA study and Weighted UniFrac analysis revealed that bacterial compositions were significantly different (999 permutations, p-value < 0.01) between the biofilm-substrata-added and biofilm-substrata-free systems. Planctomycetes were found, as key bacteria benefited from the biofilm substrata addition and exerted the major function of ammonia nitrogen control. Our study demonstrated that the addition of biofilm substrata and an external carbon source favored fish growth and improved the aquaculture environment by the formation of a unique bacteria community.

Effect of acute ammonia toxicity on inflammation, oxidative stress and apoptosis in head kidney macrophage of Pelteobagrus fulvidraco and the alleviation of curcumin

Ammonia is one of the most major pollutant and stress factors of aquaculture systems, and has seriously endangered fish health. However, few studies have been performed on mechanisms of the detrimental impact of ammonia stress and mitigation in fish. A study was carried out to investigate the response of genes involved in inflammation, antioxidation, polarization and apoptosis in head kidney macrophages to acute ammonia toxicity, and the alleviation effect of curcumin. The cells were divided into six groups, as follows: The control group composed of untreated macrophages (CON), the experimental groups, consisting of macrophages treated with 0.23 mg L^-1 ammonia (AM), 45 μmol L^-1 curcumin (CUR), 0.23 mg L^-1 ammonia and 5 μmol L^-1 curcumin (5A), 0.23 mg L^-1 ammonia and 25 μmol L^-1 curcumin (25A), 0.23 mg L^-1 ammonia and 45 μmol L^-1 curcumin (45A). The cells were pretreated with different concentrations of curcumin for 1 h and then incubated with ammonia for 24 h. The results showed that ammonia poisoning could increase ROS levels, up-regulate the expression of antioxidant enzymes (SOD and GPx), inflammatory cytokines (IL-1, IL-6 and TNF-α) and inflammatory mediators (NF-κB p65 and COX-2), decrease cell viability, down-regulate the expression of M2 marker (Arg-1) and anti-apoptosis (Bcl-2), but curcumin could alleviate the adverse effect of ammonia toxicity. Overall, these results have important implications for understanding of the mechanism of ammonia toxicity and the mitigating effect of curcumin in fish.

Application of constructed wetlands in the PAH remediation of surface water: A review

Polycyclic aromatic hydrocarbons (PAHs) pose adverse risks to ecosystems and public health because of their carcinogenicity and mutagenicity. As such, the extensive occurrence of PAHs represents a worldwide concern that requires urgent solutions. Wastewater treatment plants are not, however, designed for PAH removal and often become sources of the PAHs entering surface waters. Among the technologies applied in PAH remediation, constructed wetlands (CWs) exhibit several cost-effective and eco-friendly advantages, yet a systematic examination of the application and success of CWs for PAH remediation is missing. This review discusses PAH occurrence, distribution, and seasonal patterns in surface waters during the last decade to provide baseline information for risk control and further treatment. Furthermore, based on the application of CWs in PAH remediation, progress in understanding and optimising PAH-removal mechanisms is discussed focussing on sediments, plants, and microorganisms. Wetland plant traits are key factors affecting the mechanisms of PAH removal in CWs, including adsorption, uptake, phytovolatilization, and biodegradation. The physico-chemical characteristics of PAHs, environmental conditions, wetland configuration, and operation parameters are also reviewed as important factors affecting PAH removal efficiency. Whilst significant progress has been made, several key problems need to be addressed to ensure the success of large-scale CW projects. These include improving performance in cold climates and addressing the toxic threshold effects of PAHs on wetland plants. Overall, this review provides future direction for research on PAH removal using CWs and their large-scale operation for the treatment of PAH-contaminated surface waters.

Sub-chronic exposure to ammonia inhibits the growth of juvenile Wuchang bream (Megalobrama amblycephala) mainly by downregulation of growth hormone/insulin-like growth factor axis

In this study, healthy Wuchang bream (Megalobrama amblycephala) juveniles were exposed to 0, 5, 10, 20 and 30 mg/L total ammonia nitrogen for 30 days to elucidate toxic effects and mechanisms of ammonia on growth performance involved with the regulation of growth hormone/insulin-like growth factor (GH/IGF) and hypothalamic-pituitary-thyroid (HPT) axes. Our results showed that the increasing total ammonia nitrogen concentrations caused dose-depend decreases in the weight gain and specific growth rate but increases in the food conversion ratio and mortality in juvenile bream, indicating growth inhibitory effects induced by ammonia. Concurrently, GH, IGF-1 at protein and mRNA levels were significantly decreased in ammonia exposure groups (p < .05), while serum thyroid stimulating hormone, free thyroxine, free triiodothyronine levels were significantly reduced only in fish exposed to higher concentrations of 20 and 30 mg/L ammonia (p < .05), suggesting that ammonia exposure could perturb both GH/IGF-axis and HPT-axis functions. Furthermore, transcriptional levels of extracellular regulated protein kinases 2 (erk2), phosphatidylinositol 3-kinase (pi3k), protein kinase B (akt), target of rapamycin (tom) and ribosomal protein S6 kinase-polypeptide 1(s6k1) in the dorsal muscle were significantly down-regulated in the fish exposed to ammonia (p < .05). This fact indicated that MAPK/ERK pathway and PI3K/AKT pathway should be responsible for the growth inhibition. Combining the results of spearman correlation coefficient, it should be noted that the GH/IGF axis played a more important role in regulating the growth than the HPT axis in Wuchang bream under persistent ammonia stress.

AMP-activated protein kinase in the grass carp Ctenopharyngodon idellus: Molecular characterization, tissue distribution and mRNA expression in response to overwinter starvation stress

Adenosine monophosphate-activated protein kinase (AMPK) is the main energy sensor in mammals, but limited information is available regarding its role as an energy sensor in nutrient-restricted fish particularly in period of overwinter starvation. The present study aimed to investigate the role of AMPK in the grass carp Ctenopharyngodon idellus through characterization of AMPK full-length cDNAs and the measurement of transcriptional activity in response to overwinter starvation. AMPK is a heterotrimeric serine/threonine kinase that consists of a catalytic alpha (α) subunit complexed with two regulatory subunits, beta (β) and gamma (γ). In our study, we identified nine isoforms of the AMPK family in grass carp and obtained their complete coding sequences (CDS). In the grass carp, the α subunit is encoded by two isoforms (α1 and α2). The β and γ subunits are encoded by three (β1a, β1b, β2) and four isoforms (γ1, γ2a, γ2b, γ3), respectively. AMPK isoforms in grass carp possess structural features similar to mammalian AMPK and exhibit a high degree of homology with other fish and vertebrate AMPK sequences. The mRNA of nine grass carp AMPK isoforms were found to be expressed in a wide range of tissues in vivo, but the abundance of each AMPK mRNA demonstrated a tissue-dependent expression pattern, indicating that they might be key complexes playing the role of energy metabolism sensors during overwinter starvation conditions. Compared to expression levels in control fish (week 0), the expression of various AMPK isoforms significantly increased in the hepatopancreas of fish exposed to 1 week or more of overwinter starvation conditions as follows: week 1 (AMPK α1 and AMPK α2), week8 (AMPK β1b and AMPK γ2b), week 12 (AMPK β2 and AMPK γ1), and week 16 (AMPK β1a, AMPK γ2a, and AMPK γ3). Additionally, compared to expression levels in control fish (week 0), the expression of various AMPK isoforms significantly increased in the adipose tissue of fish exposed to 1 week or more of overwinter starvation conditions as follows: week 1(AMPK β1a and AMPK β1b), week 4 (AMPK α1, AMPK α2, AMPK γ1, AMPK γ2b and AMPK γ3), and week 8 (AMPK β2 and AMPK γ2a). Further in vitro analysis revealed that the mRNA levels of AMPK isoforms in hepatocytes (AMPK α1, AMPK α2, AMPK β1a, AMPK β1b, AMPK β2, AMPK γ2b and AMPK γ3) and adipocytes (AMPK γ2a, AMPK γ2b and AMPK γ3) changed significantly with in the first 24 h of exposure to the overwinter starvation conditions. These findings confirm that nine AMPK subunits are present in grass carp and that all encode proteins with conserved functional domains. The nine AMPK subunits are all regulated at the transcriptional levels to manage excess energy expenditure during overwinter starvation stress.

Toxicological Assessment of Ammonia Exposure on Carassius auratus red var. Living in Landscape Waters

To understand the toxic mechanism of ammonia and identify effective biomarkers on the oxidative stress for the fish Carassius auratus red var., acute and chronic toxicity tests were conducted. The 96-h LC₅₀ of total ammonia nitrogen (TAN) for C. auratus was 135.4 mg L^-1, the corresponding unionized ammonia (NH₃) concentration was 1.5 mg L^-1. The activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione-peroxidase (GSH-Px) and glutathione (GSH) showed an increase with a subsequent falling, while the malondialdehyde (MDA) increased during the chronic test. The SOD, MDA, and GSH could be effective biomarkers to evaluate the TAN oxidative stress, the maximum acceptable toxicant concentration (MATC) was 11.3 mg L^-1 for TAN. To our knowledge, this is the first study to propose biomarkers to evaluate potential environmental risk and establish a risk threshold for TAN in C. auratus.