HISTOPATHOLOGICAL EFFECTS OF PARAQUAT DICHLORIDE ON THE KIDNEY, LIVER, GILLS AND TISSUES OF TILAPIA Oreochromis niloticus FINGERLINGS

Paraquat, a non-selecting organic herbicide is used to control weeds in areas where labour is in short supply and finds its ways to aquatic systems through run-offs or its usage in integrated fish culture systems. It is quick acting and care must be taken during application. This study investigates the effects of varying concentration of the herbicide on the water quality parameters and on the kidney, gills, liver and tissue of O. niloticus fingerlings.

Fingerlings of average length and weight of 4.2cm and 0.4g were gotten from the Departmental fish farm and stocked randomly at 2L^-1 in 43 x 20cm plastic aquaria. They were acclimatized for a period of two weeks and fed twice daily at 3% body weight with 40% CP diets with feeding stopped 24 hours before commencement of bioassay. The fish were exposed to varying concentrations of herbicide at 0mgL^-1(control), 3.33mgL^-1, 6.66mgL^-1, 10mgL^-1 and 13.3mgL^-1 (table 1). The Lethal concentration (LC₅₀) after 96 hrs exposure was 4.80mg/L The mean daily water quality parameters analysed were temperature 26 ± 0.12^oC; Dissolved oxygen 6.2 ± 0.16 mg/L, pH 6.8 ± 0.11, Conductivity 176 ± 0.18 us/cm, COD 24.5 ± 0.19 mg/L and Alkalinity 33.1 ± 0.17 mg/L. Analysis of Variance observed significant differences (P<0.05) between Dissolved oxygen, COD and pH between the various concentrations and significant differences (P<0.05) in Conductivity, COD and Alkalinity between the concentrations and the control.

The Histopathological results of the exposed fish showed erosions, lesion, necrosis, malignancy, pigment and inclusion bodies in the gills, periportal hepatic degeneration, necrosis and periportal connective tissue was very prominent in the liver, severe diffuse tubular necrosis in the kidney and no visible lesions in the tissues. Varying the concentration of the toxicant resulted to respiratory stress, sudden quick movements and erratic swimming. Mortality was identified by absence of movement in fish and it increased with increase in concentration of herbicide (table 1). Dead fish were removed immediately.

Paraquat dichloride is toxic to O. niloticus and its usage on farms should be in the recommended dosage most especially in integrated fish culture systems.