Zebrafish locomotor capacity and brain acetylcholinesterase activity is altered by Aphanizomenon flos-aquae DC-1 aphantoxins

Oxidative Stress Parameters and Morphological Changes in Japanese Medaka (Oryzias latipes) after Acute Exposure to OA-Group Toxins

Toxins of the OA-group (okadaic acid, OA; dinophysistoxin-1, DTX-1) are the most prevalent in the fjords of southern Chile, and are characterized by their potential harmful effects on aquatic organisms. The present study was carried out to determine the acute toxicity of OA/DTX-1 on oxidative stress parameters in medaka (Oryzias latipes) larvae. Medaka larvae were exposed to different concentrations (1.0-30 μg/mL) of OA/DTX-1 for 96 h to determine the median lethal concentration. The LC₅₀ value after 96 h was 23.5 μg/mL for OA and 16.3 μg/mL for DTX-1 (95% confidence interval, CI was 22.56, 24.43 for OA and 15.42, 17.17 for DTX-1). Subsequently, larvae at 121 hpf were exposed to acute doses (10, 15 and 20 μg/mL OA and 5.0, 7.5 and 11.0 μg/mL DTX-1) for 96 h and every 6 h the corresponding group of larvae was euthanized in order to measure the activity levels of biochemical biomarkers (superoxide dismutase, SOD; catalase, CAT; glutathione peroxidase, GPx; and glutathione reductase, GR) as well as the levels of oxidative damage (malondialdehyde, MDA; and carbonyl content). Our results showed that acute doses caused a decrease in SOD (≈25%), CAT (≈55%), and GPx and GR (≈35%) activities, while MDA levels and carbonyl content increased significantly at the same OA/DTX-1 concentrations. This study shows that acute exposure to OA-group toxins tends to simultaneously alter the oxidative parameters that induce sustained morphological damage in medaka larvae. DTX-1 stands out as producing greater inhibition of the antioxidant system, leading to increased oxidative damage in medaka larvae. Considering that DTX-1 is the most prevalent HAB toxin in southern Chile, these findings raise the possibility of an important environmental impact on the larval stages of different fish species present in the southern fjords of the South Pacific.

Sublethal diclofenac induced oxidative stress, neurotoxicity, molecular responses and alters energy metabolism proteins in Nile tilapia, Oreochromis niloticus

Reports have shown that residues of pharmaceuticals and their metabolites can pose toxicological threats to organisms living in aquatic ecosystem. Nile tilapia, Oreochromis niloticus, was exposed at 0.17, 0.34, and 0.68 mg L^-1 of diclofenac up to 60 days in a renewal static bioassay system. Antioxidant enzymes reactions, molecular responses, activities of energy metabolism proteins, and the neurotoxic potentials of the drug in the brain and fish muscle were evaluated. Antioxidant enzyme activities such as superoxide dismutase, glutathione-S-transferase, and also fructose 1, 6 bisphosphatase and glucose-6-phosphate dehydrogenase as well as the levels of lipid peroxidation and protein carbonyl were elevated, while glutathione peroxidase, total reduced glutathione, and acetylcholinesterase in the brain and muscles of the treated groups were significantly inhibited in a dose-dependent association. Expression of superoxide dismutase (sod), catalase (cat), and heat shock proteins (hsp 70) genes in brain and muscle tissues was up-regulated. Continuous treatment with sublethal diclofenac for a long time can induce oxidative imbalance, cause neurotoxicity, and alter the expression of genes related to stress in Nile tilapia, suggesting the use of these biomarkers in monitoring the adverse effects the pharmaceuticals could cause to organisms in aquatic ecosystem for possible mitigation.

Toxicity and differential oxidative stress effects on zebrafish larvae following exposure to toxins from the okadaic acid group

Okadaic acid-group (OA-group) is a set of lipophilic toxins produced only in seawater by species of the Dinophysis and Prorocentrum genera, and characterized globally by being associated with harmful algal blooms (HABs). The diarrhetic shellfish poisoning toxins okadaic acid (OA) and dinophysistoxin-1 (DTX-1) are the most prevalent toxic analogues making up the OA-group, which jeopardize environmental safety and human health through consumption of hydrobiological organisms contaminated with these toxins that produce diarrhetic shellfish poisoning (DSP) syndrome in humans. Consequently, a regulatory limit of 160 μg of OA-group/kg was established for marine resources (bivalves). The aim of this study was to investigate effects varying concentrations of 1-15 μg/ml OA or DTX-1 on toxicity, development, and oxidative damage in zebrafish larvae (Danio rerio). After determining the lethal concentration 50 (LC₅₀) in zebrafish larvae of 10 and 7 μg/ml (24 h) and effective concentration 50 (EC₅₀) of 8 and 6 μg/ml (24 h), different concentrations (5, 6.5, or 8 μg/ml of OA and 4, 4.5, or 6 μg/ml of DTX-1) were used to examine the effects of these toxins on oxidative damage to larvae at different time points between 24 and 120 hpf. Macroscopic evaluation during the exposure period showed alterations in zebrafish including pericardial edema, cyclopia, shortening in the anteroposterior axis, and developmental delay. The activity levels of biochemical biomarkers superoxide dismutase (SOD) and catalase (CAT) demonstrated a concentration-dependent decrease while glutathione peroxidase (GPx) and glutathione reductase (GR) were markedly elevated. In addition, increased levels of oxidative damage (malondialdehyde and carbonyl content) were detected following toxin exposure. Data demonstrate that high concentrations of OA and DTX-1produced pathological damage in the early stages of development <48 h post-fertilization (hpf) associated with oxidative damage.

Effects of human-induced eutrophication on macroinvertebrate spatiotemporal dynamics in Lake Dianchi, a large shallow plateau lake in China

The Yungui Plateau lakes, which are characterized by a highly endemic biodiversity, have been suffering severely from anthropogenic intervention in the recent decades. Studies on the response of these biodiversity to human-mediated effects are still limited. Here, we selected the typical Lake Dianchi to investigate the correlation between macroinvertebrate spatiotemporal dynamics and human-induced eutrophication across a 2-year span (2009-2010). A total of 26 taxa were recorded, and the assemblage pattern of the macroinvertebrate community was mainly controlled by the spatiotemporal (region, season, and year) density fluctuations of some pollution-tolerant species (Limnodrilus hoffmeisteri, Tubifex tubifex, Branchiura sowerbyi, and Chironomus plumosus). Taxon richness, total density, biomass, and the abundance of Oligochaeta and Chironomidae decreased from the north to the south of the lake but were much higher in 2009 than in 2010. Moreover, the high densities of total assemblages and oligochaete occurred during spring and/or autumn, whereas that of chironomids was only high during summer. The contributions of important factors varied in different seasons, but the community variations were mainly shaped by eutrophication-related factors (e.g., Chla, N, and P). Variance partitioning analyses showed that aquatic factors were able to explain more community variations than sediment (6.9-36.6 vs. 5.3-14.7%) across seasons, but their interactive effects were negligible. The results of this study will be beneficial for restoring and managing hypereutrophic lakes in the Yungui Plateau and imply the necessity of long-term monitoring in bioassessment projects involving intensively disturbed lakes.

Responses of pro- and anti-inflammatory cytokines in zebrafish liver exposed to sublethal doses of Aphanizomenon flosaquae DC-1 aphantoxins

Blooms of the dominant cyanobacterium Aphanizomenon flosaquae are frequently encountered in natural waters, and their secretion of neurotoxic paralytic shellfish toxins called aphantoxins threatens environmental safety and human health worldwide. The liver is the primary detoxification organ in animals, and its pro- and anti-inflammatory responses are important functions in the detoxification of toxins. Therefore, we investigated the response of these inflammatory factors to aphantoxins in the liver of zebrafish (Danio rerio). A. flosaquae DC-1 was sampled during blooms in Dianchi Lake, China and cultured, and the toxin was extracted and analyzed using high performance liquid chromatography. The primary constituents were gonyautoxins 1 (34.04%) and 5 (21.28%) and neosaxitoxin (12.77%). Zebrafish were injected intraperitoneally with 5.3 μg (low dose) or 7.61 μg (high dose) of saxitoxin equivalents [equivalents (eq.)]/kg body weight of A. flosaquae DC-1 aphantoxins. Hyperemia, the hepatosomatic index (HSI), and physiological and molecular responses of pro- and anti-inflammatory cytokines in the zebrafish liver were investigated at different time points 1-24 h post-exposure. Aphantoxins significantly enhanced hepatic hyperemia and altered the HSI 3-24 h post-exposure, suggesting that inflammation caused morphological changes. Subsequent investigations using the enzyme-linked immunosorbent assay showed that the pro-inflammatory cytokines tumor necrosis factor-α, interleukin-1β (IL-1β), IL-6, and IL-8 and anti-inflammatory cytokines IL-10 and transforming growth factor β were higher in the liver of zebrafish exposed to aphantoxins, which indicated physiological inflammatory responses. Further analysis by real-time fluorescence quantitative polymerase chain reaction demonstrated upregulated mRNA expression of these cytokines, suggesting molecular inflammatory responses in the zebrafish liver. These changes showed dose- and time-dependent patterns. These results indicated that aphantoxins induced hyperemia and altered the HSI, and subsequently increased the levels of proinflammatory cytokines TNF-α, IL-1β, IL-6 and IL-8 to induce physiological inflammatory responses. These changes activated the anti-inflammatory cytokines IL-10 and TGF-β to suppress inflammatory damage. The induced changes were the result of upregulated mRNA expression of these inflammatory cytokines caused by aphantoxins. Aphantoxins resulted in hepatic immunotoxicity and response by inducing pro-inflammatory cytokines. Zebrafish liver in turn suppressed the inflammatory damage by upregulating the activities of anti-inflammatory cytokines. In the future, these pro- and anti-inflammatory cytokines in the zebrafish liver may be prove to be useful biomarkers of aphantoxins and blooms in nature.

The role of humic acids on gemfibrozil toxicity to zebrafish embryos

Climate change is expected to alter the dynamics of water masses, with consequent changes in water quality parameters such as dissolved organic carbon (DOC) concentration. DOC levels play a critical role in the fate of organic chemicals, influencing their bioavailability and toxicity to aquatic organisms. This study aimed to evaluate the effects of DOC, particularly humic acids (HA), in the toxicity of gemfibrozil (GEM) - a human pharmaceutical frequently detected in surface waters. Lethal and sublethal effects (genotoxic, biochemical and behavioural alterations) were evaluated in zebrafish embryos exposed to several concentrations of GEM and three HA levels, in a full factorial design. HA significantly increased GEM LC₅₀ values, mainly in the first 72 h of exposure, showing a protective effect. At sublethal levels, however, such protection was not observed since HA per se elicited adverse effects. At a biochemical level, individual exposure to HA (20 mg/L) elicited significant decreases in cholinesterase and glutathione S-transferase activities. Regarding behaviour, effects of individual exposure to HA appear to surpass the GEM effects, reducing the total distance moved by larvae. Both GEM and HA significantly increased DNA damage. Hence, this study demonstrated that abiotic factors, namely HA, should be considered in the assessment of pharmaceuticals toxicity. Moreover, it showed that lethality may not be enough to characterize combined effects since different patterns of response may occur at different levels of biological organization. Testing sublethal relevant endpoints is thus recommended to achieve a robust risk assessment in realistic scenarios.

Evaluation of 8-hydroxy-2-deoxyguanosine and NFkB activation, oxidative stress response, acetylcholinesterase activity, and histopathological changes in rainbow trout brain exposed to linuron

Linuron is a widely used herbicide to control grasses and annual broad leaf weeds. It is known that linuron has toxic effects on different organisms. However, the toxic effects of linuron on aquatic organisms, especially fish, is completely unknown. Thus, we aimed to investigate changes in 8-hydroxy-2-deoxyguanosine (8-OHdG) and nuclear factor kappa B (NFkB) activity, histopathological changes, antioxidant responses and acetylcholinesterase (AChE) activity in rainbow trout brain after exposure to linuron. Fish were exposed to 30μg/L, 120μg/L and 240μg/L concentrations of linuron for twenty-one days. Brain tissues were taken from fish for 8-OHdG and NFkB activity, histopathological examination and determination of superoxide dismutase (SOD), catalase (CAT) enzyme activity, lipid peroxidation (LPO), and reduced glutathione (GSH) levels. Our data indicated that high linuron concentrations caused a decrease in GSH levels, SOD and CAT activities in brain tissues (p<0.05). LPO levels were significantly increased by 240μg/L linuron. All concentrations caused a significant inhibition in brain AChE enzyme activity (p<0.05). Immunopositivity was detected for 8-OHdG and NFkB, and linuron exposure caused histopathological damage to the brain tissues. The results of this study can provide useful information for understanding of linuron-induced toxicity.

In vivo effects of Aphanizomenon flos-aquae DC-1 aphantoxins on gas exchange and ion equilibrium in the zebrafish gill

Aphantoxins, neurotoxins or paralytic shellfish poisons (PSPs) generated by Aphanizomenon flos-aquae, are a threat to environmental safety and human health in eutrophic waters worldwide. The molecular mechanisms of neurotoxin function have been studied; however, the effects of these neurotoxins on oxidative stress, ion transport, gas exchange, and branchial ultrastructure in fish gills are not fully understood. Aphantoxins extracted from A. flos-aquae DC-1 were detected by high-performance liquid chromatography. The major ingredients were gonyautoxins 1 and 5 and neosaxitoxin, which comprised 34.04%, 21.28%, and 12.77% of the total, respectively. Zebrafish (Danio rerio) were administered A. flos-aquae DC-1 aphantoxins at 5.3 or 7.61μg saxitoxin equivalents (eq)/kg (low and high doses, respectively) by intraperitoneal injection. The activities of Na(+)-K(+)-ATPase (NKA), carbonic anhydrase (CA), and lactate dehydrogenase (LDH), ultrastructural alterations in chloride and epithelial cells, and reactive oxygen species (ROS) and total antioxidative capacity (T-AOC) were investigated in the gills during the first 24h after exposure. Aphantoxins significantly increased the level of ROS and decreased the T-AOC in zebrafish gills from 3 to 12h post-exposure, suggesting an induction of oxidative stress and inhibition of antioxidant capacity. Reduced activities of NKA and CA demonstrated abnormal ion transport and gas exchange in the gills of aphantoxin-treated fish. Toxin administration also resulted in increased LDH activity and ultrastructural alterations in chloride and epithelial cells, suggesting a disruption of function and structure in zebrafish gills. The observed abnormalities in zebrafish gills occurred in a time- and dose-dependent manner. These findings demonstrate that aphantoxins or PSPs may inhibit ion transport and gas exchange, increase LDH activity, and result in ultrastructural damage to the gills through elevations in oxidative stress and reduced antioxidant capacity. These effects of aphantoxins in the gills of zebrafish suggest an induction of respiratory toxicity. The parameters investigated in this study may be also considered as biomarkers for studying aphantoxin/PSP exposure and cyanobacterial blooms in nature.

Respiratory toxicity of cyanobacterial aphantoxins from Aphanizomenon flos-aquae DC-1 in the zebrafish gill

Aphantoxins from Aphanizomenon flos-aquae are frequently identified in eutrophic waterbodies worldwide. These toxins severely endanger environmental safety and human health due to the production of paralytic shellfish poisons (PSPs). Although the molecular mechanisms of aphantoxin neurotoxicity have been studied, many questions remain to be resolved such as in vivo alterations in branchial histology and neurotransmitter inactivation induced by these neurotoxins. Aphantoxins extracted from a naturally isolated strain of A. flos-aquae DC-1 were determined by high performance liquid chromatography. The basic components of the isolated aphantoxins identified were gonyautoxin 1 (GTX1), gonyautoxin 5 (GTX5), and neosaxitoxin (neoSTX), which comprised 34.04, 21.28, and 12.77% of the total, respectively. Zebrafish (Danio rerio) was administrated 5.3 or 7.61mg STX equivalents (eq)/kg (low and high doses, respectively) of the A. flos-aquae DC-1 aphantoxins by intraperitoneal injection. Histological alterations and changes in neurotransmitter inactivation in the gills of zebrafish were investigated for 24h following exposure. Aphantoxin exposure significantly increased the activities of gill alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and resulted in histological alterations in the gills during the first 12h of exposure, indicating the induction of functional and structural damage. Gill acetylcholinesterase (AChE) and monoamine oxidase (MAO) activities were inhibited significantly, suggesting an alteration of neurotransmitter inactivation in zebrafish gills. The observed alterations in gill structure and function followed a time- and dose-dependent pattern. The results demonstrate that aphantoxins or PSPs lead to structural damage and altered function in the gills of zebrafish, including changes in histological structure and increases in the activities of AST and ALT. The inhibition of the activities of AChE and MAO suggest that aphantoxins or PSPs could induce respiratory toxicity in the zebrafish gill. Furthermore, these parameters may be used as bioindicators for investigating aphantoxin exposure and cyanobacterial blooms in nature.

Health Effects of Toxic Cyanobacteria in U.S. Drinking and Recreational Waters: Our Current Understanding and Proposed Direction

Cyanobacterial-derived water quality impairment issues are a growing concern worldwide. In addition to their ecological impacts, these organisms are prolific producers of bioactive secondary metabolites, many of which are known human intoxicants. To date only a handful of these compounds have been thoroughly studied and their toxicological risks estimated. While there are currently no national guidelines in place to deal with this issue, it is increasingly likely that within the next several years guidelines will be implemented. The intent of this review is to survey all relevant literature pertaining to cyanobacterial harmful algal bloom secondary metabolites, to inform a discussion on how best to manage this global public health threat.

PRMT8 as a phospholipase regulates Purkinje cell dendritic arborization and motor coordination

The development of vertebrate neurons requires a change in membrane phosphatidylcholine (PC) metabolism. Although PC hydrolysis is essential for enhanced axonal outgrowth mediated by phospholipase D (PLD), less is known about the determinants of PC metabolism on dendritic arborization. We show that protein arginine methyltransferase 8 (PRMT8) acts as a phospholipase that directly hydrolyzes PC, generating choline and phosphatidic acid. We found that PRMT8 knockout mice (prmt8 (-/-)) displayed abnormal motor behaviors, including hindlimb clasping and hyperactivity. Moreover, prmt8 (-/-) mice and TALEN-induced zebrafish prmt8 mutants and morphants showed abnormal phenotypes, including the development of dendritic trees in Purkinje cells and altered cerebellar structure. Choline and acetylcholine levels were significantly decreased, whereas PC levels were increased, in the cerebellum of prmt8 (-/-) mice. Our findings suggest that PRMT8 acts both as an arginine methyltransferase and as a PC-hydrolyzing PLD that is essential for proper neurological functions.

Neurotoxic effects of nickel chloride in the rainbow trout brain: Assessment of c-Fos activity, antioxidant responses, acetylcholinesterase activity, and histopathological changes

The aim of this study was to determine the biochemical, immunohistochemical, and histopathological effects of nickel chloride (Ni) in the rainbow trout brain. Fish were exposed to Ni concentrations (1 mg/L and 2 mg/L) for 21 days. At the end of the experimental period, brain tissues were taken from all fish for c-Fos activity and histopathological examination and determination of acetylcholinesterase (AChE), superoxide dismutase (SOD), catalase (CAT) enzyme activities, lipid peroxidation (LPO), and glutathione (GSH) levels. Our results showed that Ni treatment caused a significant increase in the brain SOD activity and in LPO and GSH levels (p < 0.05), but it significantly decreased AChE and CAT enzyme activities (p < 0.05). Strong induction in c-Fos was observed in some cerebral and cerebellar regions of fish exposed to Ni concentrations when compared with the control group. However, c-Fos activity was decreased in necrotic Purkinje cells. Brain tissues were characterized by demyelination and necrotic changes. These results suggested that Ni treatment causes oxidative stress, changes in c-Fos activity, and histopathological damage in the fish brain.

Antioxidative responses in zebrafish liver exposed to sublethal doses Aphanizomenon flos-aquae DC-1 aphantoxins

Aphanizomenon flos-aquae secretes paralytic shellfish poisons (PSPs), termed aphantoxins, and endangers environmental and human health via eutrophication of water worldwide. Although the molecular mechanism of neuronal PSP toxicity has been well studied, several issues remain unresolved, notably the in vivo hepatic antioxidative responses to this neurotoxin. Aphantoxins extracted from a natural isolate of A. flos-aquae DC-1 were resolved by high performance liquid chromatography. The primary components were gonyautoxins 1 and 5 and neosaxitoxin. Zebrafish (Danio rerio) were treated intraperitoneally with either 5.3 or 7.61 (low and high doses, respectively) μg saxitoxin (STX) equivalents (eq)/kg of A. flos-aquae DC-1 aphantoxins. Antioxidative responses in zebrafish liver were examined at different timepoints 1-24h post-exposure. Aphantoxin administration significantly enhanced hepatic malondialdehyde (MDA) content 1-12h post-exposure, indicative of oxidative stress and lipid peroxidation. By contrast, levels of reduced glutathione (GSH) in zebrafish liver declined significantly after 3-24h exposure, suggesting that GSH participates in MDA metabolism. A significant upregulation of the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) was observed, suggesting that aphantoxins induce lipid peroxidation in zebrafish liver and are likely to be hepatotoxic. Hepatic levels of MDA and GSH, and of the three enzymes (SOD, CAT, and GPx), therefore provide potential biomarkers for studying environmental exposure to aphantoxins/PSPs from cyanobacterial blooms.

Morphological alterations and acetylcholinesterase and monoamine oxidase inhibition in liver of zebrafish exposed to Aphanizomenon flos-aquae DC-1 aphantoxins

Aphanizomenon flos-aquae is a cyanobacterium that produces neurotoxins or paralytic shellfish poisons (PSPs) called aphantoxins, which present threats to environmental safety and human health via eutrophication of water bodies worldwide. Although the molecular mechanisms of this neurotoxin have been studied, many questions remain unsolved, including those relating to in vivo hepatic neurotransmitter inactivation, physiological detoxification and histological and ultrastructural alterations. Aphantoxins extracted from the natural strain of A. flos-aquae DC-1 were analyzed by high-performance liquid chromatography. The main components were gonyautoxins 1 and 5 (GTX1, GTX5) and neosaxitoxin (neoSTX), which comprised 34.04%, 21.28%, and 12.77% respectively. Zebrafish (Danio rerio) were exposed intraperitoneally to 5.3 or 7.61 μg STX equivalents (eq)/kg (low and high doses, respectively) of A. flos-aquae DC-1 aphantoxins. Morphological alterations and changes in neurotransmitter conduction functions of acetylcholinesterase (AChE) and monoamine oxidase (MAO) in zebrafish liver were detected at different time points 1-24h post-exposure. Aphantoxin significantly enhanced hepatic alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities and histological and ultrastructural damage in zebrafish liver at 3-12 h post-exposure. Toxin exposure increased the reactive oxygen species content and reduced total antioxidative capacity in zebrafish liver, suggesting oxidative stress. AChE and MAO activities were significantly inhibited, suggesting neurotransmitter inactivation/conduction function abnormalities in zebrafish liver. All alterations were dose- and time-dependent. Overall, the results indicate that aphantoxins/PSPs induce oxidative stress through inhibition of AChE and MAO activities, leading to neurotoxicity in zebrafish liver. The above parameters may be useful as bioindicators for investigating aphantoxins/PSPs and cyanobacterial blooms in nature.

Lipid peroxidation and antioxidant responses in zebrafish brain induced by Aphanizomenon flos-aquae DC-1 aphantoxins

Aphanizomenon flos-aquae is a cyanobacterium that is frequently encountered in eutrophic waters worldwide. It is source of neurotoxins known as aphantoxins or paralytic shellfish poisons (PSPs), which present a major threat to the environment and human health. The molecular mechanism of PSP action is known, however the in vivo effects of this neurotoxin on oxidative stress, lipid peroxidation and the antioxidant defense responses in zebrafish brain remain to be understood. Aphantoxins purified from a natural isolate of A. flos-aquae DC-1 were analyzed using high performance liquid chromatography. The major components of the toxins were gonyautoxins 1 and 5 (GTX1 and GTX5, 34.04% and 21.28%, respectively) and neosaxitoxin (neoSTX, 12.77%). Zebrafish (Danio rerio) were injected intraperitoneally with 7.73 μg/kg (low dose) and 11.13 μg/kg (high dose) of A. flos-aquae DC-1 aphantoxins. Oxidative stress, lipid peroxidation and antioxidant defense responses in the zebrafish brain were investigated at various timepoints at 1-24h post-exposure. Aphantoxin exposure was associated with significantly increased (>1-2 times) reactive oxygen species (ROS) and malondialdehyde (MDA) in zebrafish brain compared with the controls at 1-12h postexposure, suggestive of oxidative stress and lipid peroxidation. In contrast, reduced glutathione (GSH) levels in the zebrafish brain exposed to high or low doses of aphantoxins decreased by 44.88% and 41.33%, respectively, after 1-12h compared with the controls, suggesting that GSH participated in detoxification to ROS and MDA. Further analysis showed a significant increase in the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) compared with the controls, suggesting elimination of oxidative stress by the antioxidant response in zebrafish brain. All these changes were dose and time dependent. These results suggested that aphantoxins or PSPs increased ROS and MDA and decreased GSH in zebrafish brain, and these changes induced oxidative stress. The increased activity of SOD, CAT and GPx demonstrated that these antioxidant enzymes could play important roles in eliminating excess ROS and MDA. These results also suggest that MDA, ROS, GSH and these three antioxidant enzymes in the brain of zebrafish may act as bioindicators for investigating A. flos-aquae DC-1 aphantoxins or PSPs and algal blooms in nature.