Histopathological and ultrastructural alterations in some organs of Oreochromis niloticus exposed to glyphosate-based herbicide, Excel Mera 71

Sole and co-exposure toxicity of commercial formulations ethoprophos and bispyribac-sodium to Oreochromis niloticus: Assessment of oxidative stress, genotoxicity, and gill ultrastructure

Aquatic organisms are simultaneously exposed to multiple hazardous chemicals that can be released into water bodies. The current study aimed to evaluate the effect of sublethal concentration (1/50 96 h-LC50) of two formulated pesticides: ethoprophos, bispyribac-sodium, and their combination for 1, 2, 3, and 4 weeks on oxidative stress, genotoxic response, and gill morphology in Nile tilapia. This study is the first to demonstrate the toxic effects of ethoprophos and bispyribac-sodium mixture on the commercial important species, Oreochromis niloticus. The results showed that the 96 h-LC50 values of ethoprophos and bispyribac-sodium were 4.8 and 0.064 mg/L, respectively. Additionally, exposure to individual or combined pesticides induced a significant increase in the level of malondialdehyde (MDA), glutathione S-transferase (GST), and 8-hydroxy-2-deoxyguanosine (8-OHdG), as well as a notable decline in reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) levels at all time of exposure. Furthermore, there were alterations in ultrastructure of the gill samples, including erosive lesions on the primary and secondary lamellae, fusion of microridges, and excessive mucus secretions on the epithelium. The data clearly demonstrate that the negative effects of the tested compounds are time-dependent and are more severe in combination than in a single compound. Collectively, our results indicated that the interaction of ethoprophos and bispyribac-sodium might be largely synergistic and provide new insights into the molecular mechanisms of fish confronting these substances.

Ameliorating effect of ascorbic acid on fenvalerate induced ultrastructural changes in scales, erythrocytes and gills of Ctenopharyngodon idella (Valenciennes, 1844)

Fenvalerate (type II synthetic pyrethroid), widely used in agricultural practices, find its way into aquatic ecosystem through air, by runoff, or by percolation to groundwater. It is an extremely toxic insecticide for aquatic organisms especially fish. In the present study, the fenvalerate (FEN) induced toxicity and the protective efficacy of ascorbic acid (AA) against FEN in Ctenopharyngodon idella was evaluated by studying the structural alterations in scales, erythrocytes and gills. The fishes were exposed to 1.2 μg/L and 2 μg/L of FEN and orally administered with 1000 mg/kg diet of AA. The fishes were scrutinized on 15^th, 30^th and 60^th day of experiment. Scanning electron microscopic studies (SEM) of FEN-treated fish revealed extensive morphological alterations on the microstructure of scales including deformed focus, uprooted lepidonts and tubercles, hole formation and worn out calcareous material from the surface. FEN intoxication induced severe damage on erythrocytes including formation of dacrocytes, serrated spherocytes, echinocytes with oozed out cytoplasmic content, contracted plasma membrane and appearance of lobopodial projections. Ultrastructural studies in gills declared profound lesions in the form of aneurysm, loss of secondary lamellae and destructed microstructures of pavement cells. On the other hand, supplementation of AA in diet mitigated the impairment provoked by FEN on the scales, erythrocytes and gills due to its antioxidant properties.

Comparative toxicity of chlorpyrifos: Sublethal effects on enzyme activities and histopathology of Mugil cephalus and Chanos chanos

Ecotoxicological data and potential impact of chlorpyrifos (CPF) in the region are scarce for prescribing safety limits. Therefore, toxicity and sublethal impact of CPF on fish fingerlings of Mugil cephalus (3.0 ± 1.2 cm) and Chanos chanos (3.0 ± 1.5 cm) were studied. Acute and chronic toxicity tests were conducted by continuous flow through method and derived 96 h median lethal concentration (LC₅₀). Mean LC₅₀ value of 1.13 μg/L for M. cephalus, and 3.20 μg/L for C. chanos were derived by Probit. Chronic toxicity tests were conducted for 30 days and determined no observed effect concentration values of 0.09 μg/L 0.17 μg/L and lowest observed effect concentration values of 0.16 μg/L 0.32 μg/L and chronic values of 0.13 μg/L 0.25 μg/L for M. cephalus and C. chanos respectively. Key biomarker enzyme activities viz., EST, SOD and MDH were studied at sublethal concentrations of CPF. Native gel electrophoresis revealed gradual decrease in isoforms of EST and SOD activities, whereas MDH activity increased in fingerlings. These responses indicate inhibition of cholinesterase, antioxidants and synthesis of ATPs in the cells due to CPF stress. Pathological lesions were evaluated in gill and eye tissues of fingerlings. Epithelial fusion and degenerative changes were prominent in primary lamellae. Hyperplasia, lifting epithelium, fusion of lamellae and necrosis were evidenced in the secondary lamellae. Cellular anomalies in the retina of the eye of C. chanos include vacuoles in nerve fiber layer, shrinkage of outer plexiform layer and detachment of pigment epithelium layer. These changes indicate physiological disturbance in the gill and eye.