Abstract:
This study is carried out to determine the acute toxicity of Paraquat dichloride on hybrid catfish, Heteroclarias. 250 healthy juveniles (25±0.02 g and 6.8±0.06 cm) were exposed to five concentrations (2.00, 2.10, 2.20, 2.30 and 2.40 mL of paraquat dichloride/10 L) converted to 0.00, 0.552, 0.5796, 0.6072, 0.6348 and 0.6624 mg/L) in replicates for 96 hours bioassay acute toxicity test. Indices such as water quality parameters (pH, temperature, conductivity, and dissolved oxygen), histology examinations (gills, liver, and kidney), haematology parameters (PCV, HB, RBC, WBC, MCV, MCH, and MCHC), behavioural responses and LC50 were observed and recorded. Data collected were subjected to analysis of variance while the median lethal concentration was determined using Probit analysis. Results showed that Paraquat dichloride impacted negatively on the observed indices as the concentration increases; pH, temperature, conductivity and dissolved oxygen of the treated groups deviated markedly from the control (p>0.05). Histopathological examination of the gills revealed severe erosion and heavy sloughing off gill filaments, loss of epithelial cells and secondary lamellae, atrophy; liver changes include lesions, monocytes congestion, mild degeneration to necrosis of hepatocytes while chronic inflammation, hyperplasia and necrosis were observed in the kidney. Estimated blood parameters (PCV, RBC, HB, MCV) showed a decreasing trend while WBC increasing and computed parameters (MCH, MCHC) were sinusoidal across the treatments. Behavioural responses ranged from rapid opercula movements, restlessness, mucuos discharge, haemorrhage and discolouration, bloated belly, loss of balance and reflex intensified as concentrations increased. LC50 obtained after 96 hours was 2.30 mL of toxicant/10 L or (0.6348 mg/L) while the specific dose that kill hybrid fish, Heteroclarias is 2.238 mL of toxicant/10 L or 0.6177 mg/L. Mortality of test fish at lowest concentration (2.00 mL of toxicant/10 L) was 10% while it was 80% at highest (2.40 mL of toxicant/10 L) concentration. Thus, this study revealed that Paraquat dichloride was toxic to
Heteroclarias fish. Therefore, its application should be limited (to expertise use) and or monitored or controlled to avoid imminent eco-toxicological hazards.
