Acute toxicity, behavioural and histological changes in juvenile <i>clarias gariepinus</i> exposed to atrazine

Abstract

The study determined acute toxicity, behavioural changes and histological effects of atrazine on juvenile Clarias gariepinus. The  experiment involved exposing groups of fish to different concentrations {0.00 (control), 3.75, 6.25, 8.75, 11.25 and 13.75mg/l} of atrazine  and monitoring fish mortality, physicochemical parameters of the test water and behavioural changes in the fish. The histological  assessment of liver and gills was also carried out on dead fish to examine possible changes in their structural makeup in comparison to  the organ extracted from the control. Acute toxicity test was conducted using standard methods and fish mortality was monitored for 96  hours. The physico-chemical parameters such as temperature, pH, dissolved oxygen, total dissolved solids and electrical conductivity in  the test solutions were monitored using standard procedure. The study revealed that there was no mortality in the control group, which  had no atrazine, while mortality rates increased with increasing concentrations of atrazine. The highest percentage mortality (83.33%)  was recorded at the highest concentration of 13.75mg/l. The 96- hour lethal concentration (LC₅₀) value of atrazine computed based on  logarithm was 8.84mg/l. At exposure to acute concentrations, fish showed abnormal behaviour such as restlessness, loss of colouration, respiratory stress, erratic swimming and instant death. Histological effects observed on the gills exposed to atrazine included interstitial  haemorrhage, deformed primary and secondary lamella, lesion, blanketing and blood congestion. Liver tissues showed necrosis and  vacuolation of hepatocytes. Dissolved oxygen level in the test solutions that contained atrazine reduced drastically and this might have  induced death in fish recorded in the study. Inference from the study revealed that atrazine may be toxic to aquatic organisms,   particularly juvenile C. gariepinus.