Oxygen in its molecular state O2, is essential for many metabolic processes that are vital to aerobic life. Aerobic organisms cannot exist without oxygen, which nevertheless is inherently dangerous to their lives. Like all aerobic organisms, fish are also susceptible to the effects of reactive oxygen and have inherent and effective antioxidant defenses that are well described in the literature. This review investigates the influence of different biotic and abiotic factors (age, phylogenetic position, feeding behavior, environmental factors, oxygen, temperature, presence of xenobiotics) on antioxidant defenses in fish. Studies of antioxidant activity in fish open a number of novel research lines providing greater knowledge of fish physiology, which will benefit various aspects of fish farming and artificial production.

Antioxidant Defenses in Fish: Biotic and Abiotic Factors

Carbon nitride (g-C3N4) has attracted great attention for its wide applications in hydrogen evolution and photocatalytic degradation. In this study, phosphorus doped porous ultrathin carbon nitride nanosheets (PCN-S) were prepared successfully via the element doping and thermal exfoliation method. The prepared PCN-S was characterized by XRD, SEM, TEM, N2-adsorption-desorption measurement, FT-IR, XPS, UV–vis diffuse reflectance spectra, photoluminescence (PL), photocurrent response (I-t) and EIS. The results show that PCN-S owns regular crystal structure of g-C3N4, large specific surface areas and nanosheet structure with lots of in-plane pores on its surface, excellent chemical stability, and broad light response to the whole visible light region, which was attributed to the doping of phosphorus element. Under visible light irradiation, the photocatalytic reduction of Cr(VI) over different samples indicated that the P doping and porous nanosheet structure play an important role for the enhanced performance of PCN-S. The reason was that P element doping can broaden the visible light response region, and large specific surface areas from the porous nanosheet structure can provide quantities of active sites for the photocatalytic reaction. Then the detailed study on the PCN-S for simultaneous photocatalytic reduction of Cr(VI) and oxidation of 2,4-diclorophenol (2,4-DCP) was conducted. The experiments results show that low pH value and enough dissolved oxygen were found to promote Cr(VI) reduction and 2,4-DCP oxidation. The detailed photocatalytic mechanism was proposed. The strategies used in this study could provide new insight into the design of g-C3N4 based materials with high photocatalytic activity, and present potential for the treatment of Cr(VI)/2,4-DCP or other mixed pollutants in wastewater.

Insight into highly efficient simultaneous photocatalytic removal of Cr(VI) and 2,4-diclorophenol under visible light irradiation by phosphorus doped porous ultrathin g-C3N4 nanosheets from aqueous media: Performance and reaction mechanism

Local mussels, Perna viridis, were transplanted from a relatively clean site to various polluted sites in Hong Kong. After a 30-day field exposure, different antioxidant parameters including glutathione S transferase (GST), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), NADPH DT-diaphorase (DT-d), glutathione (GSH) and lipid peroxidation were quantified, and tissue concentrations of benzo[a]pyrene (B[a]P) as well as a total of five polycyclic aromatic hydrocarbons (PAHs) with potential carcinogenicity were determined for individual mussels. Results indicated that: (1) tissue concentrations of B[a]P and total PAHs from the same site were highly variable; (2) gill SOD, DT-d and lipid peroxidation showed no response to tissue pollutants: (3) the majority of the antioxidant parameters were induced by increasing tissue pollutant concentrations; and (4) amongst the various parameters, oxyradical scavenger GSH [ best correlated with tissue concentrations of pollutants.

Relationships between tissue concentrations of polycyclic aromatic hydrocarbons and antioxidative responses of marine mussels, Perna viridis

Glyphosate [N-(phosphonomethyl) glycine] is a broad spectrum, post emergent herbicide and is among the most widely used agricultural chemicals globally. Initially developed to control the growth of weed species in agriculture, this herbicide also plays an important role in both modern silviculture and domestic weed control. The creation of glyphosate tolerant crop species has significantly increased the demand and use of this herbicide and has also increased the risk of exposure to non-target species. Commercially available glyphosate-based herbicides are comprised of multiple, often proprietary, constituents, each with a unique level of toxicity. Surfactants used to increase herbicide efficacy have been identified in some studies as the chemicals responsible for toxicity of glyphosate-based herbicides to non-target species, yet they are often difficult to chemically identify. Most glyphosate-based herbicides are not approved for use in the aquatic environment; however, measurable quantities of the active ingredient and surfactants are detected in surface waters, giving them the potential to alter the physiology of aquatic organisms. Acute toxicity is highly species dependant across all taxa, with toxicity depending on the timing, magnitude, and route of exposure. The toxicity of glyphosate to amphibians has been a major focus of recent research, which has suggested increased sensitivity compared with other vertebrates due to their life history traits and reliance on both the aquatic and terrestrial environments. This review is designed to update previous reviews of glyphosate-based herbicide toxicity, with a focus on recent studies of the aquatic toxicity of this class of chemicals.

Impact of glyphosate and glyphosate‐based herbicides on the freshwater environment

Methyl parathion (MP) is an organophosphorus insecticide used worldwide in agriculture and aquaculture due to its high activity against a broad spectrum of insect pests. The effect of a single exposure to 2 mg L − 1 of a commercial formulation of MP (MPc: Folisuper 600®, MP 600 g L − 1 ) on catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD), glutathione S -transferase (GST), reduced glutathione (GSH) and lipid peroxidation (LPO) of the liver, white muscle and gills of Brycon cephalus was evaluated after 96 h of treatment. MPc exposure resulted in a significant induction of SOD, CAT and GST activity in all tissues. However, the GPx activity decreased significantly in white muscle and gills, whereas no alterations were observed in hepatic GPx activity. MPc also induced a significant increase in LPO values in the white muscle and gills, while hepatic LPO levels did not show any significant alteration. The current data suggest that MPc has oxidative-stress-inducing potential in fish, and that gills and white muscle are the most sensitive organs of B. cephalus , with poor antioxidant potentials. The various parameters studied in this investigation can also be used as biomarkers of exposure to MPc.

Oxidative stress biomarkers in the freshwater characid fish, Brycon cephalus, exposed to organophosphorus insecticide Folisuper 600 (methyl parathion)

Effects of chronic exposure of 2,4-dichlorophenol on the antioxidant system in liver of freshwater fish Carassius auratus.

Bioaccumulation and antioxidant responses in goldfish Carassius auratus under HC Orange No. 1 exposure.

This is the first report of the antioxidant response of Daphnia magna following a short-term response to the water soluble fractions of no. 20 diesel oil. Daphnia magna was exposed for 24h to nominal concentrations of 0, 0.005, 0.01, 0.05, 0.1, 0.5 or 1.0 mg/L diesel oil. Following this exposure, the activities of catalase (CAT) and glutathione S-transferase (GST) were induced significantly on the whole compared to control group; the activity of selenium-dependent glutathione peroxidase (Se-GPx) were inhibited significantly on the whole; the activity of superoxide dismutase (SOD) only responded to diesel oil exposure at the two highest exposure concentrations; the activity of glutathione reductase (GR) and the content of reduced glutathione (GSH) were greatly activated in Group 4; and the content of oxidized glutathione (GSSG) were induced at two different concentrations. Total glutathione (tGSH) and GSH/GSSG ratio were also calculated to analyze the occurrence of oxidative stress. In conclusion, ...

Antioxidant response of Daphnia magna exposed to no. 20 diesel oil

The effects of low level zinc(Zn 2+)and its EDTA complex on zinc accumulation and antioxidant enzymes,such as catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), glutathione peroxidase (GPx) in the liver of Carassius auratus are studied after 40 day exposure. The results show that zinc accumulation is significantly increased with higher zinc concentration. When fish are exposed to Zn-EDTA, the zinc accumulation in the liver of fish increased slightly according to the control. SOD, GST, CAT and GPx activity all decrease with adding to Zn 2+ and Zn-EDTA in waters. However, the decrease of CAT and GPx activities of fish liver are alleviated with the addition of EDTA. The GST activities increased at lower concentration solutions (0.05mg·L -1), however its activities were inhibited at higher Zn 2+ solution (0.05mg·L -1). These results suggest that CAT and GPx are more sensitive to low zinc exposure than SOD and GST, and they can be served as biomarkers of low concentration zinc exposure in aquatic ecosystem.

[Effects of long-term exposure of low level zinc and zn-EDTA complex on zinc accumulation and antioxidant defense system in liver of Carassius auratus].

The effects of copper (Cu 2+ ) and Cu-EDTA complex on the induction of HSP70 in the fish brain were studied.After the fish (Carassius auratus) were exposed to the experimental concentrations for forty days , the SDS-PAGE and Western Blotting techniques were used to detect the expression level of HSP70 in the fish brain.The results showed that Cu 2+ and Cu-EDTA complex can induce the expression of HSP70 significantly.Comparing with the test groups exposed to Cu 2+,the Cu-EDTA complex had changed the bioavailability and decreased the toxicity of the heavy metal.It was found that the fish exposed to the concentration of Cu 2+ which below the national fishery water quality standard of 0.01mg/L , also had a significant increase in the expression level of HSP70. Therefore, HSP70 as an environmental biomarker can be a more sensitive and rapid indicator than conventional end points in the aquatic ecosystem.

Hua Shen

Papers

Effects of chronic exposure of 2,4-dichlorophenol on the antioxidant system in liver of freshwater fish Carassius auratus.

Bioaccumulation and antioxidant responses in goldfish Carassius auratus under HC Orange No. 1 exposure.

Antioxidant response of Daphnia magna exposed to no. 20 diesel oil

[Effects of long-term exposure of low level zinc and zn-EDTA complex on zinc accumulation and antioxidant defense system in liver of Carassius auratus].

[Effects of copper (Cu2+) and Cu-EDTA complex on the induction of HSP70 in the fish brain].