A 49 days experiment was conducted under laboratory condition to ascertain the effects of technical grade glyphosate on behaviour and histopathological conditions in the gills of red hybrid tilapia using light inverted microscope. Air gasping, erratic swimming, fin movement, mucus secretion, hemorrhages and loss of scales were observed in the exposed fish. There was no any histopathological complication observed in the gill of the control fish, but various level of alterations were seen in the gills of the fish exposed to glyphosate herbicide. These include lifting of primary lamella, congestion of secondary lamella as well as hyperplasia in both primary and secondary gill lamella and hypertrophy of secondary gill lamella. Based on the findings of this study, glyphosate herbicide exerts behavioural and histopathological changes in the gill of red hybrid tilapia, and therefore the fish is considered as good bioindicator in aquatic environment monitoring.
The lethal concentration (LC50) was determined and found to be 215 mg/L, the mean water quality parameters were temperature, 26-29?, dissolved oxygen, 5.3-9.3 mg/L, and pH, 6.5-7.3 respectively. Three (3) concentrations of glyphosate were prepared for the purpose of the experiment (0, 50, and 150 mg/L). Behavioral changes was constantly recorded at daily basis. At the end of exposure period, the gill of the fish was removed and prepared for histopathological evaluation using light inverted microscopy.
The outcome of the study revealed various behavioural changes such as air gasping, erratic swimming, fin movement, mucus secretion, hemorrhages and loss of scales were observed. There were also many histopathological alterations in the gills of the fish. There was no histopathological changes observed in the gill of the control fish (Figure 1A). Fish exposure to glyphosate concentration of 50 mg/L caused the lifting of primary and congestion of the secondary gill lamellae (Figure 1B). A further increase in glyphosate concentration to 150 mg/L resulted in hyperplasia and hypertrophy of primary and secondary gill lamella and vacuolation of the secondary gill lamellae (Figure 1C).