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The toxic effects of 2, 4-dichlorophenol (2, 4-DCP) on aquatic organisms are well-established; however, the details regarding the mechanisms underlying the toxicity, especially immunotoxicity are poorly understood. Consequently, the aim of this study was to investigate the histopathologic, oxidative stress and immunotoxic effects attributed to exposure to sublethal concentrations of 2,4-DCP in the African catfish, Clarias gariepinus. Juvenile C. gariepinus were exposed to 0.4, 0.8, or 1.6 mg/L 2, 4-DCP for 28 days after which blood and head kidney were extracted for the determination of various nonspecific innate immune parameters while the liver was excised for histopathology examination and measurement of oxidative stress biomarkers. Control fish were maintained in water spiked 10 µL/L ethanol, representing the solvent control. A significant increase was noted in the activities of lactate dehydrogenase and superoxide dismutase as well as in levels of lipid peroxidation and DNA fragmentation in a dose-dependent manner, with higher adverse effects observed at the highest concentration tested (1.6 mg/L). The total white blood cells (WBC) count was significantly elevated in fish exposed to 2,4-DCP compared to control. Myeloperoxidase content was decreased significantly in fish exposed to 2,4-DCP especially at the highest concentration (1.6 mg/L) compared to controls. The respiratory burst activity did not differ markedly amongst groups. Histopathological lesions noted included edema, leucocyte infiltration, and depletion of hemopoietic tissue in the head kidney of exposed fish. There was significant upregulation in the mRNA expression of tumor necrosis factor (TNF-α) and heat shock protein 70 (HSP 70) but downregulation of major histocompatibility complex 2 (MHC 2) in exposed fish. Data demonstrated that exposure to 2,4-DCP resulted in histopathological lesions, oxidative stress, and compromised immune system in C. gariepinus. [ABSTRACT FROM AUTHOR]

The objective of the study was to determine the comparative toxicities and immune dysfunction in the African catfish, Clarias gariepinus, exposed to bisphenol A (BPA) and its two analogues: bisphenol AP (BPAP) and bisphenol P (BPP). Juveniles of C. gariepinus were exposed to sublethal concentrations (70 and 140 μg/L) of BPA, BPAP and BPP for 7, 14 or 21 days after which various endpoints which are indicative of cytotoxicity, oxidative stress and haematological and innate immune parameters were determined in the liver homogenates or blood plasma. The exposure of C. gariepinus to BPA and its analogues caused significant increased activities of lactate dehydrogenase, catalase and superoxide dismutase. The exposed fish had increased levels of DNA fragmentation, lipid peroxidation, white blood cells, nitric oxide and respiratory burst, while the red blood cell counts and the percentage packed cell volume decreased significantly in the exposed fish compared to control. The toxic effects elicited by the bisphenols were both concentration- and duration-dependent. Generally, BPA exerted the most toxic effects on the fish, followed by BPAP, while BPP exerted the least toxic effects to C. gariepinus. Summarily, the findings indicated that BPA and its two analogues studied in the research are capable of causing cytotoxicity, oxidative stress and immune dysfunction in C. gariepinus. [ABSTRACT FROM AUTHOR]

The pathogenic enterobacterium, Serratia marcescens, is a potential fish pathogen having been isolated in fish culturing environments. However, information on its effects on the physiology of cultured fish species is scarce. This study therefore aimed at ascertaining the physiological status of African catfish (Clarias gariepinus) that has been experimentally challenged with S. marcescens. Healthy juvenile C. gariepinus were experimentally challenged with either 1 × 104 CFU/ml or 5 × 104 CFU/ml inoculums of S. marcescens via oral gavage and the hematological (percentage packed cell volume (PCV), red blood cells (RBC) counts, white blood cells (WBC), counts and differential leucocytes counts) and innate humoral (plasma levels of nitric oxide and respiratory burst) parameters were determined at 4 h, 24 h, 48 h, and 14 days post-challenge periods. The control fish were gavaged with distilled water. The bacterial-challenged fish had significantly higher WBC counts, and increased levels of plasma nitric oxide and respiratory burst while the RBC counts and the PCV decreased significantly in the bacterial-challenged fish compared to control. The response of the fish to bacterial challenge is both inoculum size- and duration-dependent. The incubation of C. gariepinus with 5 × 104 CFU/mL inoculums of S. marcescens elicited more effects in the fish compared to the control or 1 × 104 CFU/mL group. The results of this study showed that infection with S. marcescens has the potential to modulate the immune system of the fish with the inflammatory pathways playing an important role in the defense of the fish against bacterial infection. [ABSTRACT FROM AUTHOR]

The possibility of ultraviolet (UV) photooxidation of cypermethrin generating more toxic intermediates or isomers demands that studies that look at the effects of cypermethrin and UV irradiation under a coexposure scenario be carried out. In this study, juvenile African catfish (Clarias gariepinus) were exposed to 50 µg/L cypermethrin, 100 µg/L cypermethrin, UV, 50 µg/L cypermethrin + UV or 100 µg/L cypermethrin + UV, in a static renewal for 3 weeks. The control fish were maintained in uncontaminated water, and not exposed to UV radiation. After the exposure duration, the fish were killed, and the activities of acid phosphatase, alkaline phosphatase, amylase, protease, and lipase were determined in the liver or intestinal homogenates. Also, the histopathology of some sections of the intestine was performed. The results showed that the activities of the enzymes decreased significantly following exposure to cypermethrin while there was no change in the activities of the enzymes due to UV irradiation alone. The histopathological analyses indicated that exposure to cypermethrin caused alterations in the histoarchitecture of the fish such as severe erosion of the mucosa layer, faded lamina propria, and disintegration of the muscle layer. The exposure of fish to both cypermethrin and UV irradiation caused significant decrease in the activities of the enzymes. This could be an indication that UV irradiation has the tendency to potentiate cypermethrin‐induced toxicity in fish. Research Highlights: The exposure of C. gariepinus to cypermethrin caused significant decrease in the activities of important metabolic enzymes, and altered the histoarchitecture of the intestine. UV exposure potentiated cypermethrin‐induced toxic effects in the fish. [ABSTRACT FROM AUTHOR]

The contamination of aquatic ecosystem with heavy metals and pesticides has increased dramatically over the years, and this has generated a lot of attention by environmental experts. There are reports on impacts of different single toxicants on aquatic organisms but not much has been done to investigate the impacts of mixtures of toxicants on aquatic life. In this study we investigated the effects of multiple stressors of Pb and cypermethrin on ionoregulation in the African catfish (Clarias gariepinus). Adults C. gariepinus were exposed to either borehole water (control), 2 mg/L Pb, 0.5 μg/L cypermetrin or a mixture of 2 mg/L Pb and 0.5 μg/L cypermethrin for 96 h, after which the levels of plasma Na+, Cl- and K+ were determined as a measure of branchial ionoregulatory disturbance. The exposure of C. gariepinus to 0.5 μg/L cypermethrin resulted in a significant reduction in plasma Na+ (43% decrease) and Cl- (31% decrease) but a 2-fold increase in plasma K+ concentrations. Exposure to a mixture of cypermethrin and Pb resulted in 53% decrease in plasma Na+, 40% decrease in plasma Cl- and a 3- fold increase in plasma K+. There was no significant difference between the control and those exposed to just only 2 mg/L Pb for all the parameters measured. The results of this study indicated that exposure of aquatic organisms to combined stressors of heavy metals pollution as well as pesticide contaminantion could have a serious effect on the physiology especially on ionic regulation in the exposed fish. [ABSTRACT FROM AUTHOR]

Cypermethrin and chlorpyrifos are broad-spectrum insecticides routinely used as household and agricultural insecticides. Since aquatic environments serve as sinks for numerous environmental pollutants, the effects of these substances on the resident aquatic organisms can be quite serious. In this study, we investigated the effects of exposure of African catfish to cypermethrin and chlorpyrifos on oxidative damage and the activity of glutathione S-transferase (GST). Juvenile African catfish were exposed to 1.25 μg/L cypermethrin, 1.25 μg/L chlorpyrifos, 2.5 μg/L cypermethrin or 2.5 μg/L chlorpyrifos for 96 h. Control fish were maintained in borehole water. At the end of the 96 h exposure, tissue lipid peroxidation (LPO), protein carbonylation and GST activities were determined. Contaminant exposure resulted in a significant increase (p < 0.05) in the levels of LPO and protein carbonylation and the activity of GST in the gills, liver and muscle of exposed fish compared to the controls. Oxidative damage was more serious in the groups exposed to chlorpyrifos compared to those exposed to cypermethrin, thus implying that chlorpyrifos is more toxic to these fish than cypermethrin. The results of this study indicate that the pollution of aquatic ecosystems with cypermethrin and chlorpyrifos may cause oxidation of biomolecules (lipids and proteins) that are involved in essential physiological and biochemical activities in animals. [ABSTRACT FROM AUTHOR]

The African catfish (Clarias gariepinus) is a widely cultured fish species in many African countries because of its rich nutritional quality. In this study, the impacts of exposure to common environmental contaminants; a heavy metal (Lead) and a pyrethroid insecticide (Cypermethrin) on the biochemical contents of C. gariepinus was investigated. Juveniles of C. gariepinus were exposed to borehole water (control), 2 mg/L Pb, 0.5 µg/L cypermethrin or 2 mg/L Pb + 0.5 µg/L cypermethrin for 96 h after which the total protein levels, glycogen contents and total cholesterol in the liver and muscle were determined. Fish exposure to cypermethrin and a mixture of cypermethrin and Pb resulted in a significant decrease in glycogen and protein levels but a significant increase in the cholesterol levels in liver and muscle (p < 0.05). There was no significant difference between the control and the group exposed to 2 mg/L Pb. The glycogen and total cholesterol levels were significantly higher in the liver in groups exposed to cypermethrin and the mixture of cypermethrin and Pb (p < 0.05) while the total protein levels were higher in the muscle, although this difference was not statistically significant. The results of this study suggest that environmental pollution of aquatic environments have adverse effects on the health of resident fish as well as other aquatic life. [ABSTRACT FROM AUTHOR]