The impact of sub-lethal concentrations of glyphosate on growth and haematology of African catfish under aquatic ecological micro-climate

Abstract

The impact of sub-lethal concentrations of glyphosate (Isopropylamine salt - H2NCH(CH3)2) an active ingredient in Roundup® herbicides on growth and haematology of African catfish (Clarias gariepinus) were evaluated under aquatic ecological envirornment. Uncontrolled discharge of glyphosate from agricultural farm land to aquaculture facilities necessitated the study. Sub-lethal concentrations 0.30 mg/l, 0.50 mg/l, 0.70 mg/l and 1.40 mg/l were established after series of range finding tests. Weight (g) and length measurement (cm) were taken on biweekly basis to monitor growth. Behavioural responses to treatment during the range finding tests includes: erratic swimming, loss of balance, mucous secretion, discolouration, hanging on water surface and inactivity. Blood parameters analyzed were Red Blood Cell (RBC), Haemoglobin content (Hb), Packed Cell Volume (PCV), White Blood Cell (WBC), Platelet (PLT), Mean Corpuscular Volume (MCV), Mean Corpuscular Haemoglobin (MCH) and Mean Corpuscular Haemoglobin Concentration (MCHC). Automated haematology analyser was used to determine the blood parameters. The physico-chemical parameters monitored were temperature, pH, Dissolved Oxygen and Electrical Conductivity. Thermometer, pH meter, dissolved oxygen meter and Electrical conductivity meter respectively were used. The findings of the study demonstrated that exposure for 60 days to the herbicide “glyphosate” at sub-lethal doses of 0.30 mg/l, 0.50 mg/l, 0.70 mg/l and 1.40 mg/l were toxic to Clarias gariepinus and this toxicants were dose-dependent.There was significant difference (P < 0.05) in growth among the treatments. The best growth was recorded in the control (0.00 mg/l) while poorest growth was recorded in 1.40 mg/l. The findings in this study showed that 0.30 mg/l to 1.40 mg/l of the toxicants were harmful to Clarias gariepinus. The report therefore recommended examination of lower concentrations (<0.30 mg/l) in future study to establish the limit beyond which glyphosate should not be allowed in aquaculture system.