Chronic Ammonia Exposure Research Articles

Activation autophagy enhances ammonia detoxification by boosting urea and glutamine synthesis in yellow catfish (Pelteobagrus fulvidraco)

The study explores how activating autophagy in yellow catfish under chronic ammonia stress (CAS) can boost growth and improve ammonia detoxification, addressing the serious threat of ammonia stress on fish survival and disease susceptibility in aquatic settings. Yellow catfish (Pelteobagrus fulvidraco) weighing 2.35 ± 0.13 g were divided into three groups over an 8-week period: CON group without ammonia exposure, AM group exposed to 50 mg/L total ammonia nitrogen (T-AN), and AM+RAPA group fed diets with 3 mg/100 g rapamycin under 50 mg/L T-AN. Dietary rapamycin (DR) can alleviate growth retardation, liver structural damage, inflammation, apoptosis, decreased detoxification capacity, and reduced survival rate caused by CAS. Additionally, DR can mitigate autophagy inhibition induced by CAS. Metabolomics analysis revealed that activation of autophagy by DR significantly alleviated the glutamate, aspartate n-acetyl-l-glutamate, ornithine, argininosuccinate, and citrulline levels in the liver induced by CAS. This suggests that autophagy activation can supplement these metabolites involved in urea and glutamine synthesis, thereby promoting ammonia detoxification. In conclusion, liver autophagy is a vital mechanism for ammonia detoxification as it facilitates the synthesis of urea and glutamine. Moreover, it offers a theoretical foundation for addressing the negative effects of chronic ammonia exposure in aquaculture.

α-lipoic acid ameliorates hepatotoxicity induced by chronic ammonia toxicity in crucian carp (Carassius auratus gibelio) by alleviating oxidative stress, inflammation and inhibiting ERS pathway

High environment ammonia (HEA) poses a deadly threat to aquatic animals and indirectly impacts human healthy life, while nutritional regulation can alleviate chronic ammonia toxicity. α-lipoic acid exhibits antioxidative effects in both aqueous and lipid environments, mitigating cellular and tissue damage caused by oxidative stress by aiding in the neutralization of free radicals (reactive oxygen species). Hence, investigating its potential as an effective antioxidant and its protective mechanisms against chronic ammonia stress in crucian carp is highly valuable. Experimental fish (initial weight 20.47 ± 1.68 g) were fed diets supplemented with or without 0.1% α-lipoic acid followed by a chronic ammonia exposure (10 mg/L) for 42 days. The results revealed that chronic ammonia stress affected growth (weight gain rate, specific growth rate, and feed conversion rate), leading to oxidative stress (decreased the activities of antioxidant enzymes catalase, superoxide dismutase, glutathione peroxidase; decreased total antioxidant capacity), increased lipid peroxidation (accumulation of malondialdehyde), immune suppression (decreased contents of nonspecific immune enzymes AKP and ACP, 50% hemolytic complement, and decrease of immunoglobulin M), impaired ammonia metabolism (reduced contents of Glu, GS, GSH, and Gln), imbalance of expression of induced antioxidant-related genes (downregulation of Cu/Zu SOD, CAT, Nrf2, and HO-1; upregulation of GST and Keap1), induction of pro-apoptotic molecules (transcription of BAX, Caspase3, and Caspase9), downregulation of anti-apoptotic gene Bcl-2 expression, and induction of endoplasmic reticulum stress (upregulation of IRE1, PERK, and ATF6 expression). The results suggested that the supplementation of α-lipoic acid could effectively induce humoral immunity, alleviate oxidative stress injury and endoplasmic reticulum stress, and ultimately alleviate liver injury induced by ammonia poisoning (50–60% reduction). This provides theoretical basis for revealing the toxicity of long-term ammonia stress and provides new insights into the anti-ammonia toxicity mechanism of α-lipoic acid.

The Requirement and Protective Effects of Dietary Protein against Chronic Ammonia Exposure in Juvenile Genetically Improved Farmed Tilapia (Oreochromis niloticus).

Ammonia is a key risk factor in intensive aquaculture systems. This experiment is aimed at investigating the influence of dietary protein levels on genetically improved farmed tilapia (GIFT, Oreochromis niloticus) under chronic ammonia stress. GIFT juveniles of 4.00 ± 0.55 g were exposed to high ammonia level at 0.88 mg/L and fed with six diets comprising graded protein levels at 22.64%, 27.26%, 31.04%, 35.63%, 38.47%, and 42.66% for 8 weeks. The fish in negative control was fed the diet with 31.04% protein in normal water (0.02 mg ammonia/L water). Our results showed that high ammonia exposure (0.88 mg/L) caused significant decrease in fish growth performance, hematological parameters, liver antioxidant enzymes (catalase and glutathione peroxidase), and gill Na+- and K+-dependent adenosine triphosphatase (Na+/K+-ATP) activity. When fish were under high ammonia exposure, the weight gain rate, special growth rate, feed efficiency, and survival rate elevated significantly with dietary protein supplementation increase to 35.63%, whereas protein efficiency ratio, hepatosomatic index, and viscerosomatic index showed a decreased tendency. Dietary protein administration significantly enhanced crude protein but reduced crude lipid contents in the whole fish. Fish fed diets with 35.63%-42.66% protein had higher red blood cell counts and hematocrit percentage than fish fed 22.64% protein diet. The values of serum biochemical indices (lactate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase), hepatic antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase), and gill Na+/K+-ATP activity were all elevated with the increment of dietary protein. Moreover, histological analysis indicated that dietary protein administration could prevent the ammonia-induced damages in fish gill, kidney, and liver tissues. Based on weight gain rate as a response criterion, the optimal dietary protein requirement for GIFT juveniles under chronic ammonia stress was 37.9%.

Adverse effects of chronic ammonia stress on juvenile oriental river prawn (Macrobrachium nipponense) and alteration of glucose and ammonia metabolism.

Ammonia is one of the common stress factors in aquaculture. However, the effect of chronic ammonia exposure in juvenile oriental river prawn (Macrobrachium nipponense) is currently unexplored. This study explored the effects of chronic ammonia on juvenile healthy oriental river prawns. Fifty prawns (0.123 ± 0.003 g) were exposed to 0, 5, and 15 mg/L total ammonia nitrogen (TAN) in triplicates for 28 days. The effects of chronic ammonia challenge were evaluated on growth, antioxidant capacity, hepatopancreas and gill morphology, and glucose and ammonia metabolism. The results showed that, the chronic ammonia exposure reduced significantly survival rate and weight gain of prawns. The prawns exposed to 15 mg/L ammonia had induced oxidative stress. However, the prawn exposed to 15 mg/L ammonia had significantly lower aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and acid phosphatase activities in the serum. Furthermore, exposure of prawns to 15 mg/L ammonia increased the activities of hexokinase, pyruvate kinase, pyruvate and lactic acid content, and glutamine synthase activity. However, the prawns exposed to 15 mg/L ammonia, reduced succinic dehydrogenase, 6-phosphogluconic dehydrogenase, phosphoenolpyruvate carboxykinase, glutamate synthase, and glutamate dehydrogenase activities but increased ammonia content in serum. The exposure of ammonia deformed lumen, damaged basement membrane and decreased secretory cells in the hepatopancreas, disordered gill epithelial and pillar cells, and caused gill filament base vacuolation. Our study indicates that chronic ammonia stress impairs growth performance, tissue morphology, induces oxidative stress, and alters glucose and ammonia metabolism in juvenile oriental river prawns.

Effects of Chronic Ammonia Exposure on Growth of Genetically Improved Farmed Tilapia (GIFT) Cultured Under Different Densities

AbstractTilapia are among the most widely cultivated fish species in the world, with a high level of importance for freshwater fish production. An important tilapia variety for the international market is genetically improved farmed tilapia (GIFT; Nile Tilapia Oreochromis niloticus). Multiple studies have been developed to determine the maximum concentrations of ammonia (NH3) recommended for the cultivation of various varieties of tilapia; however, there are no specific data for the cultivation of GIFT. Growth results for GIFT fry exposed to NH3 at 0.50, 0.89, and 1.58 mg/L in 69‐d chronic toxicity tests were evaluated. The experiments were conducted in three recirculation aquaculture systems, one for each concentration of NH3. Stocking densities were 33, 66, and 132 fish/m3. Fish were fed ad libitum three times per day. The only mortalities recorded were for treatments with the highest NH3 concentration (1.58 mg/L), which had a cumulative mortality of 89.5%. There were no significant differences in weight gain for the three stocking densities assessed at an NH3 concentration of 0.50 mg/L. Results indicated that GIFT juveniles can be cultured with stocking densities of up to 132 fish/m3 in environments with ammonia concentrations of up to 0.89 mg/L without compromising fish survival, although the daily weight gain was between 30% and 41% lower than the values reported for optimal culture conditions.

The effects of acute and chronic ammonia exposure on growth, survival, and free amino acid abundance in juvenile Japanese sea perch Lateolabrax japonicus

Japanese sea perch, Lateolabrax japonicus is an economically important marine fish and is widely cultured in coastal area of China. In recent years, ammonia poisoning has seriously affected the yield and quality of perch, but data on its ammonia tolerance is sparse. This study used a sequential approach to evaluate how perch tolerate acute and chronic ammonia exposure. First, we estimated the effects of acute ammonia poisoning on perch (16.08 ± 0.12 g) and calculated 96-h LC50 that, based on linear interpolation (y = 2.64× – 99.11, R2 = 0.94 where y = % mortality and x = mg L−1 T-AN ammonia concentration), was 56.50 mg L−1 total ammonia nitrogen (T-AN). Then we measured the 42-d survival, growth and concentration of free amino acids in muscle of perch (16.12 ± 0.95) g reared in 0.00, 0.28, 0.57, 1.13 and 2.06 mg L−1 T-AN. The survival rate decreased when ammonia concentration exceeded 0.57 mg L−1 T-AN, but the weight gain, condition factor and hepatosomatic index were inhibited when ammonia concentration exceeded 0.28 mg L−1 T-AN. The changes in free amino acids concentration may be potentially related to the ammonia exposure. We recommend that Japanese sea perch not be exposed to ammonia concentrations >0.28 mg L−1 T-AN for prolonged periods of time.

Evaluation of Ammonia Nitrogen Exposure in Immune Defenses Present on Spleen and Head-Kidney of Wuchang Bream (Megalobrama amblycephala).

Ammonia is one of the most important environmental factors in aquatic ecosystems. However, there are limited studies on the effects of chronic or long-term ammonia stress and its potential molecular mechanism in fish. This study aimed to investigate the immune response and molecular mechanisms in the spleen and head-kidney of fish following chronic ammonia exposure. Megalobrama amblycephala (9.98 ± 0.48 g) were exposed to different concentrations of total ammonia nitrogen (0–30 mg/L) for 30 days. Ammonia exposure caused significant increases in cortisol levels and decreases in lysozyme and complement 3/4 concentrations in the serum, indicating inhibitory effects of ammonia stress on innate immune responses. Ammonia exposure also induced concentration-dependent increases in ammonia concentrations in tissue, pathological damage and indexes of spleen and head-kidney. Additionally, the contents of immunoglobulin M (IgM), interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) as well as mRNA levels of toll-like receptors (TLRs)/Myeloid differentiation factor 88 (MyD88)-independent signaling molecules in the spleen and head-kidney were significantly downregulated after ammonia exposure. Our findings suggested that chronic ammonia exposure caused the suppression of innate and adaptive immune responses through downregulating TLR/MyD88-independent signaling. Adverse influences of chronic ammonia stress were more severe in the spleen than in the head-kidney.

Sub-lethal and lethal effects of chronic ammonia exposure and hypoxia on a New Zealand bivalve

Eutrophication-induced hypoxia is among the most widespread anthropogenically deleterious environmental issues occurring globally in coastal marine environments, contributing to a suite of major stressors on marine organisms. Changes to biogeochemical processes and loss of biodiversity and ecosystem function are symptoms of stressors on aerobic organisms, particularly in estuaries. The response of a species to a single stressor is often very different when compared to exposure in a multiple stressor environment. Using an experimental approach, we tested the sub-lethal and lethal effects of hypoxia and chronic nutrient enrichment on the critical estuarine bivalve Austrovenus stutchburyi. Findings of the present study highlight the cumulative mortality of A. stutchburyi nearly doubled when exposed to elevated ammonia when it was combined with elevated hypoxic stress. A positive feedback loop is hypothesized to explain the result, whereby A. stutchburyi stressed by low oxygen produce and excrete more ammonia waste, increasing their risk of mortality and subsequent lethal ammonia concentrations. Water samples taken across the 45-day experiment support the hypothesis, with ammonia concentrations differing between treatments with bivalves in hypoxic treatments producing more ammonia than normoxic treatments. Siphon activity and respiration rate responses to hypoxic stress also demonstrated the importance of hypoxia as a primary driver of stress responses by A. stutchburyi. These findings highlight the threats to estuarine ecosystems with bivalve populations, whereby, extensive degradation of algal mats results in increased oxygen consumption from microbial respiration, which leads to hypoxia and shallowing of the oxygenated layer. Consequently, chemical reduction in sediments can be associated with an efflux of ammonium into the water column. The experimental results presented here on interactions between stressors highlights the substantial detrimental implications for bivalve populations and subsequent ecosystem functions given increased prevalence of warming and eutrophication in estuaries and coastal environments.

Chronic exposure to ammonia induces oxidative stress and enhanced glycolysis in lung of piglets.

Ammonia is one of the major environmental pollutants in the pig industry that seriously affects the airway health of pigs. In this study, we aimed to investigate the metabolic profiling changes of piglets' lung tissue after the exposure of 0 ppm (CG), 20 ppm (LG) and 50 ppm (HG) ammonia for 30 days. Compared with the control group, the obvious lung lesions were observed in HG, including interstitial thickening, inflammatory cell infiltration and focal hemorrhage. The significantly increased content of malondialdehyde in HG, combined with the significantly decreased mRNA expression of antioxidase and inflammatory-regulators in exposure groups, implied that ammonia exposure induced oxidative stress and diminished the anti-inflammatory response in lung tissues. Metabolomic analyses of lung tissues revealed 15 significantly altered metabolites among the three groups including multiple amino acids, carbohydrates and lipids. The accumulation of succinic acid, linoleic acid and phosphorylethanolamine and consumption of glucose, quinolinic acid and aspartic acid in ammonia exposure groups, indicated that energy supply from glucose aerobic oxidation was suppressed and the glycolysis and lipolysis were activated in lung tissues induced by chronic ammonia exposure.

Exploring the Multimodal Role of Yucca schidigera Extract in Protection against Chronic Ammonia Exposure Targeting: Growth, Metabolic, Stress and Inflammatory Responses in Nile Tilapia (Oreochromis niloticus L.).

Simple SummaryAmmonia is a problematic environmental toxicant for aquatic species. The current study aimed to declare the modulatory effect(s) of YSE against chronic ammonia intoxication in Nile tilapia through its effects on growth performance, haemato-biochemical and antioxidant-related parameters, and histopathological changes, as well as the molecular gene expression of some genes related to appetite and growth, glucose and lipid metabolism and some inflammatory cytokines. Our results indicated that Yucca schidigera extract alleviated the adverse impacts induced by ammonia intoxication. YSE could be used as a functional water supplement in aquaculture.Ammonia is a critical hazardous nitrogen metabolic product in aquaculture. Despite trials for its control, ammonia intoxication remains one of the most critical issues to overcome. In this study, we explored the modulatory effect and potential mechanism by which Yucca schidigera extract (YSE) can ameliorate ammonia intoxication-induced adverse effects on tilapia health and metabolism. A total number of 120 Nile tilapia were evenly assigned into four groups with three replicates each. The first group served as normal control group; the second group was exposed to ammonia alone from the beginning of the experiment and for four weeks. The third group was supplied with YSE in water at a dose of 8 mg/L and exposed to ammonia. The fourth group was supplied with YSE only in water at a dose of 8 mg/L. YSE supplementation succeeded in improving water quality by reducing pH and ammonia levels. Moreover, YSE supplementation markedly alleviated chronic ammonia-induced adverse impacts on fish growth by increasing the final body weight (FBW), specific growth rate (SGR), feed intake and protein efficiency ratio (PER) while reducing the feed conversion ratio (FCR) via improvements in food intake, elevation of hepatic insulin-like growth factor (ILGF-1) and suppression of myostatin (MSTN) expression levels with the restoration of lipid reserves and the activation of lipogenic potential in adipose tissue as demonstrated by changes in the circulating metabolite levels. In addition, the levels of hepato-renal injury biomarkers were restored, hepatic lipid peroxidation was inhibited and the levels of hepatic antioxidant biomarkers were enhanced. Therefore, the current study suggests that YSE supplementation exerted an ameliorative role against chronic ammonia-induced oxidative stress and toxic effects due to its free radical-scavenging potential, potent antioxidant activities and anti-inflammatory effects.

Survival strategies of Wuchang bream (Megalobrama amblycephala) juveniles for chronic ammonia exposure: Antioxidant defense and the synthesis of urea and glutamine

This study aimed to explore how Wuchang bream (Megalobrama amblycephala) survive and defend against the toxicity of ambient total ammonia nitrogen (0, 5, 10, 20 and 30 mg/L TA-N) during 30-day exposure. As a result, hepatic malondialdehyde and protein carbonylation as well as histopathological alterations increased with increasing TA-N level, which suggested that chronic ammonia exposure caused oxidative stress and damage in the liver of fish. Meanwhile, the activities of hepatic total superoxide dismutase (T-SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glucose 6-phosphate dehydrogenase (G6PD) as well as the mRNA expression of Cu/Zn sod, cat, gpx and g6pd were elevated significantly along with significant reduction of glutathione (GSH) and nicotinamide adenine dinucleotide phosphate (NADPH) (P < 0.05). These results indicated that hepatic antioxidant responses were activated to alleviate oxidative damages induced by ammonia, in which lower-concentration ammonia only initiate SOD-CAT-GR-G6PDH defense and higher ammonia activated the SOD-CAT-GPx-GSH-GR-G6PDH antioxidant response. In addition, significant increases of serum urea and hepatic ammonia, urea, glutamine, arginase as well as glutamine synthetase were detected with the increase of TA-N (P < 0.05), while serum ammonia levels kept stable (P > 0.05). The present findings further revealed that ammonia could be detoxified directly into glutamine and urea in Wuchang bream to cope with ammonia exposure. In conclusion, under chronic ammonia exposure, enhanced hepatic antioxidant responses as well as increased urea and glutamine synthesis worked in combination to allow Megalobrama amblycephala to defend against environmental ammonia toxicity.

Stress regulation and tolerance in shrimp: The transcriptomic and physiological response to chronic ammonia exposure in the black tiger shrimp, Penaeus monodon

Stress regulation and tolerance in shrimp: The transcriptomic and physiological response to chronic ammonia exposure in the black tiger shrimp, Penaeus monodon

The effect of chronic ammonia exposure on acute-phase proteins, immunoglobulin, and cytokines in laying hens

Ammonia (NH3) is a potential health hazard to both humans and animals, causing local and systemic low-grade inflammation based on its levels and exposure durations. The objective of this study was to examine the effects of 45 wk of exposure to 30 ppm NH3 on the concentrations of acute-phase proteins, immunoglobulins, and cytokines in laying hens. At 18 wk of age, a group of Hy-Line W-36 hens was randomly assigned to 4-hen cages. These cages were evenly divided between 2 environmentally controlled chambers. At 25 wk of age, one chamber was maintained continuously with fresh air (NH3 < 5 ppm; control group) and the other one was injected with NH3 and controlled at 30 ppm (NH3 group) for 45 wk. At 70 wk of age, blood and spleen samples (n = 8 per treatment) were collected for analyses of immunological parameters. No significant differences were observed in plasma levels of albumin, complement components (C)-3 and C-4, immunoglobulin (Ig)M, IgA and IgG, interleukin (IL)-6, IL-10, or interferon gamma in the NH3 group compared to control group. Compared to control hens, NH3 exposed hens had higher plasma levels of α-1-acid glycoprotein (24%) and tumor necrosis factor alpha (54%) and higher mRNA expression of IL-1β (47%) and IL-6 (62.5%) in the spleen. These results indicated that hens may have the capability to adapt to chronic effects of moderate levels of NH3. Future studies should explore acute effects of NH3 at higher levels on hen health and welfare.

Effects of chronic ammonia exposure on ammonia metabolism and excretion in marine medaka Oryzias melastigma

Ammonia is highly toxic to aquatic organisms, but whether ammonia excretion or ammonia metabolism to less toxic compounds is the major strategy for detoxification in marine fish against chronic ammonia exposure is unclear to date. In this study, we investigated the metabolism and excretion of ammonia in marine medaka Oryzias melastigma during chronic ammonia exposure. The fish were exposed to 0, 0.1, 0.3, 0.6, and 1.1 mmol l−1 NH4Cl spiked seawater for 8 weeks. Exposure of 0.3–1.1 mmol l−1 NH4Cl had deleterious effects on the fish, including significant reductions in growth, feed intake, and total protein content. However, the fish could take strategies to detoxify ammonia. The tissue ammonia (TAmm) in the 0.3–1.1 mmol l−1 NH4Cl treatments was significantly higher than those in the 0 and 0.1 mmol l−1 NH4Cl treatments after 2 weeks of exposure, but it recovered with prolonged exposure time, ultimately reaching the control level after 8 weeks. The amino acid catabolic rate decreased to reduce the gross ammonia production with the increasing ambient ammonia concentration. The concentrations of most metabolites remained constant in the 0–0.6 mmol l−1 NH4Cl treatments, whereas 5 amino acids and 3 energy metabolism-related metabolites decreased in the 1.1 mmol l−1 NH4Cl treatment. JAmm steadily increased in ambient ammonia from 0 to 0.6 mmol l−1 and slightly decreased when the ambient ammonia concentration increased to 1.1 mmol l−1. Overall, marine medaka cope with sublethal ammonia environment by regulating the tissue TAmm via reducing the ammonia production and increasing ammonia excretion.

Chronic ammonia exposure does not influence hepatic gene expression in growing pigs

Housed pigs are often exposed to elevated concentrations of atmospheric ammonia. This aerial pollutant is widely considered to be an environmental stressor that also predisposes to reduced growth rates and poor health, although evidence to support this view is limited. Hepatic gene expression is very responsive to stress and metabolic effects. Two batches of growing pigs were therefore exposed to a nominal concentration of atmospheric ammonia of either 5 ppm (low) or 20 ppm (high) from 4 weeks of age for 15 weeks. Growth rates were monitored. Samples of liver were taken after slaughter (at ∼19 weeks of age). Samples from the second batch were analysed for global gene expression using 23 K Affymetrix GeneChip porcine genome arrays. Samples from both batches were subsequently tested for five candidate genes using quantitative real-time PCR (qPCR). The array analysis failed to detect any significant changes in hepatic gene expression following chronic exposure to atmospheric ammonia. Animals clustered into two main groups but this was not related to the experimental treatment. There was also no difference in growth rates between groups. The qPCR analyses validated the array results by showing similar fold changes in gene expression to the arrays. They revealed a significant batch effect in expression of lipin 1 (LPIN1), Chemokine (C-X-C motif) ligand 14 (CXCL14), serine dehydratase (SDS) and hepcidin antimicrobial peptide (HAMP). Only CXCL14, a chemotactic cytokine for monocytes, was significantly down-regulated in response to ammonia. As chronic exposure to atmospheric ammonia did not have a clear influence on hepatic gene expression, this finding implies that 20 ppm of atmospheric ammonia did not pose a significant material risk to the health or metabolism of housed pigs.

Acute Toxicity of Copper, Zinc, and Ammonia to Larvae (Glochidia) of a Native Freshwater Mussel Echyridella menziesii in New Zealand

Adult New Zealand freshwater mussel Echyridella menziesii were collected from three locations in the North Island of New Zealand. In a series of tests that followed standard test guidance, glochidia were exposed to either dissolved copper (Cu), zinc (Zn), or total ammonia nitrogen (TAN) for 6, 24, or 48 h (20 °C, pH 7.8, water hardness 30 mg L(-1) as CaCO3, dissolved organic carbon [DOC] 2.0-2.9 mg L(-1)). Of the three contaminants and tests that met control survival criteria, mussel larvae (glochidia) were most sensitive to Cu exposure (48-h EC50 = 1.7-3.4 μg L(-1), 48-h no observed effect concentrations (NOEC) of 1.3-2.6 μg L(-1)). The Zn 48-h EC50 concentrations were 229-337 μg L(-1) and the 48-h NOEC values were 128-240 μg L(-1). Compared with other native New Zealand species, glochidia were also relatively sensitive to TAN exposure (48-h EC50 12-15 mg TAN L(-1) [pH 7.8], 48-h NOEC 8-10 mg TAN L(-1)). Comparison of our data with those of previous studies on North American freshwater mussels indicates that (1) E. menziesii are among those aquatic species most sensitive to acute Cu or TAN exposure; and (2) E. menziesii juveniles would not be adequately protected by current ANZECC water quality guidelines for TAN or Cu. Inclusion of North American juvenile mussel data in a revision of the current ANZECC water-quality guideline (95th percentile) for chronic ammonia exposure results in a decrease from 0.9 mg to 0.2 mg TAN L(-1) (pH 8).

Effect of chronic ammonia exposure on locomotor activity in the fiddler crab Uca princeps upon artificial tides and light cycles

The aim of this study was to evaluate the effect of continuous exposure to sublethal ammonia concentrations upon the characteristics of the locomotor activity rhythms in Uca princeps, exposed to artificial tides and light cycles. Adult male crabs were used for standardized 24 h ammonia acute toxicity tests. Sublethal ammonia concentrations were selected considering the results obtained in the acute bioassays as well as the unusual high ammonia concentrations registered in their natural habitat. Three independent groups of eight crabs each were exposed during 15–20 days to 0.125, 3.5, and 18 mg N-TA/L in artificial sea water. Locomotor activity was recorded individually by means of infrared light crossings. Artificially created tidal and light–dark cycles were used along the experiments. The 24 h-LC50 was 186.02 mg N-TA/L. No mortality was registered in the crabs exposed to the sublethal ammonia concentrations. In control groups, organisms showed tidal activity onset mainly in low tide (ebb) and no response to light cycles while ammonia exposed crabs shifted their onset of activity to high tide, and a general increasing activity was observed along the experiment. The obtained results indicate that ammonia affects the entraining features of the tidal activity rhythm and demonstrate that under ammonia sublethal exposure, tides may present relative coordination with light cycles in the tidal activity rhythm of the crabs.

The inhibitory effect of environmental ammonia on Danio rerio LPS induced acute phase response

Ammonia is a toxic by-product of amino acid catabolism and a common environmental pollutant that has been associated with increased disease susceptibility in fish although the mechanism is not well understood. We addressed the hypothesis that elevated environmental ammonia acts by impairing the acute phase response (APR). Specifically, we determined the impact of sub-lethal acute (24 h) and chronic (14 d) ammonia exposure on acute phase protein gene expression in zebrafish ( Danio rerio) in response to a challenge with bacterial lipopolysaccharide (LPS: i.p. 10 μg/g after 24 h). A panel of LPS-responsive genes (SAA, HAMP, LECT2, Hp and IL1β) were identified and evaluated by real-time quantitative PCR. Ammonia was found to impair induction of SAA, HAMP and LECT2 by 50–90%. Both short (15 min, 1 h and 24 h) and long-term (14 days) exposure to high environmental ammonia concentrations significantly elevated whole-body cortisol levels compared with control fish. Our results reveal for the first time that exposure to high environmental levels of ammonia suppresses the innate immune response in fish. We hypothesize that high environmental ammonia-mediated elevation of cortisol levels in zebrafish may be playing a key role in this immunosuppression, while the mechanisms involved remains to be elucidated.

Oxidative stress and antioxidant enzymes in liver and white muscle of Nile tilapia juveniles in chronic ammonia exposure

Oxidative stress and antioxidant enzyme activities in liver and white muscle of Nile tilapia ( Oreochromis niloticus) juveniles (10 ± 1.2 g) in chronic exposure to sublethal total ammonia nitrogen (TAN) were studied. The fish were exposed to the TAN concentrations, 5 mg L −1 (low) or 10 mg L −1 (high) for consecutive 70 days at 26 ± 0.5 °C temperature. At the end of experimental period, lipid peroxidation and protein carbonylation levels and the activities of xanthine oxidase (XO), aldehyde oxidase (AO), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), glutathione reductase (GR), γ-glutamyl cysteinyl synthetase (γ-GCS), and γ-glutamyl transpeptidase (γ-GT) in liver and white muscle were assayed. The levels of oxidative stress biomarkers and the activities of the enzymes assayed were significantly increased in liver and white muscle of fish exposed to both low and high TAN levels. The changes in these parameters were intensified at high TAN level. The significance of these alterations in enzyme activities is discussed.

Effects of chronic and periodic exposure to ammonia on growth and blood physiology in juvenile turbot ( Scophthalmus maximus)

Juvenile turbot ( Scophthalmus maximus) were exposed periodically and chronically to different levels of un-ionised ammonia (UIA-N) and the subsequent effect on growth and food conversion efficiency was studied. Fish with a mean (SD) initial weight 19.3 (3.9) g, were exposed to five treatments consisting of a control group, two groups (ChronicLow and ChronicHigh, UIA-N levels of 0.13 and 0.25 mg l − 1 , respectively) chronically exposed to ammonia and two groups (LowPulse and HighPulse) exposed to the same levels as above for a short period daily. The fish were held for 64 days at 18 °C, a pH of 8.04 and a salinity of 33.5‰. At the end of the experiment, fish from the Control group had a significantly higher mean weight (95.5 g) compared to all other groups. Fish from the ChronicHigh group displayed the lowest mean weight (74.6 g), whereas fish in the ChronicLow, LowPulse and HighPulse groups displayed mean weights of: 79.3 g, 82.8 g and 81.9 g, respectively. Blood ion concentrations were not affected significantly in any of the treatments, whereas minor reductions in blood pH, partial pressure of CO 2 and total CO 2 content were found in ammonia exposed groups up until day 44 of the experiment. Feed conversion efficiency, daily feeding rate and total feed consumption did not vary significantly between treatments. The study demonstrate that short daily ammonia peaks may result in negative effects on growth, equivalent to that found under chronic ammonia exposure in juvenile turbot.