TOXIC EFFECTS OF GLYPHOSATE AND PARAQUAT TO JUVENILES OF THE AFRICAN CLARIID CATFISH CLARIAS GARIEPINUS (TEUGELS, 1986)
TOXIC EFFECTS OF GLYPHOSATE AND PARAQUAT TO JUVENILES OF THE AFRICAN CLARIID CATFISH CLARIAS GARIEPINUS (TEUGELS, 1986)
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Date
2015-01
Authors
AYANDA, Opeyemi Isaac
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Abstract
The impact of short and long term exposure to the commonly used herbicides, glyphosate and paraquat on Clarias gariepinus juveniles was evaluated using standard methods that assessed fish behaviour, mortality, biochemical, histological, cytotoxic and genotoxic parameters. Fish exhibited some behavioural abnormalities such as hyperactivity, hitting of tails against the walls of the holding medium and abnormal swimming. The herbicides caused mortality of fish in a concentration dependent manner for the duration of exposure to acute concentrations of both herbicides for 96hrs. The LC50 value for paraquat by probit method/analyses was 0.07mg/L while that of glyphosate was 0.53mg/L, hence paraquat was more toxic than glyphosate. Fractions, 0.0035, 0.007, 0.014mg/L paraquat and 0.0265, 0.053 and 0.106mg/L glyphosate representing 1/20, 1/10 and 1/5 respectively of these LC50 values were used for a 56day chronic exposure study following a static renewal protocol. Samples for biochemical analysis, pathology, cytotoxicity and genotoxicity were collected at intervals of 14days respectively. Assessment of biochemical parameters revealed significant increases (p≤0.05) in the activities of stimulating liver enzymes, Alanine Aminotransferase (ALT), Aspartate Aminotransferase (AST), Lactate Dehydrogenase (LDH) and Alkaline Phosphatase (ALP) in all experimental groups compared with control exposures. There were also significant increases (p≤0.05) in the activities of the antioxidant enzymes Catalase (CAT), Superoxide dismutase (SOD), Glutathione Peroxidase (GPx) and in lipid peroxidation which was measured by thiobarbituric reactive substances (TBARS). These increases were either dose dependent, time dependent, or both. The increase in the activities of these enzymes was slightly more in paraquat-treated than in glyphosate-treated fishes indicating that paraquat is more toxic to C. gariepinus. Histological analysis of the fish organs examined revealed varying degrees of pathological alterations/degerations to the gills, liver and the brain in both the short and long term study. The gills of fish showed alterations like sloughing off and thickening of lamella. The liver exhibited changes such as vacuolar degeneration of hepatocytes, hepatocyte swelling and necrosis. In the brain, neuronal degeneration of neutrophils, gliosis amongst others were observed. The blood cells, following herbicide treatment showed the presence of
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micronucleus, fragmented apoptotic cells, bean-shaped cells and lobed nucleus. The percentages (0.56% in control and 1.80% in the highest concentration for glyphosate; 0.61% in control and 1.57% in the highest concentration for paraquat in the acute study) of these different alterations increased with increasing concentration and with time in both the short and long term exposure experiments. The genotoxic analysis showed damage to fish DNA, particularly in fish exposed to acute concentrations of both herbides. The damage to fish DNA observed during the short term exposure was greater compared to damage in the long term study. The study therefore revealed that exposing Clarias gariepinus juveniles to acute and sublethal concentrations of glyphosate and paraquat upset metabolic, cytological and nuclear morphology in Clarias gariepinus and implies poor environmental fitness for fish exposed to herbicides in natural environments.
Description
A DISSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES,
AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF
DOCTOR OF PHILOSOPHY IN FISHERIES
DEPARTMENT OF BIOLOGICAL SCIENCES,
FACULTY OF SCIENCE
AHMADU BELLO UNIVERSITY,
ZARIA, NIGERIA
Keywords
TOXIC EFFECTS,, GLYPHOSATE,, PARAQUAT,, JUVENILES,, AFRICAN CLARIID CATFISH,, CLARIAS GARIEPINUS (TEUGELS, 1986)