ABSTRACT
Fish are particularly sensitive to a wide variety of agrochemicals including glyphosate herbicide that may arise from not only deliberate discharge of these chemicals into waterways but also from approved agricultural practices. The toxic effects of glyphosate on Clarias gariepinus juveniles of mean weight 10.05 ± 1.50 g and mean length of 10.75 ± 1.80 cm were investigated for a period of 12 weeks. The concentrations of the toxicant were prepared as 0.00 (control), 39.02, 78.04, 156.09, 312.19 and 624.39 mg/L with replicates each for the acute effects of glyphosate for mortality rate and behavioural responses for 96 period hours. Behavioural, haematological, histopatological, growth and physico-chemical analysis were carried out based on standard experimental procedures. Percentage treatments from LC50 were determined as follows: 00 (control), 23, 38, 53, 68 and 83 mg/L, respectively using the LC50 of the toxicant which was 151.36 mg/L. The physical and behavioural changes of the exposed fishes occurred as the concentration increased; restlessness, uncoordinated movement, air gasping, discolouration of the skin and eventual death. The haematological study indicated a significant reduction in White Blood Cells (WBC) and Packed cell Volume (PCV) counts with increased concentrations of the toxicant. In the liver, the enlargement of the hepatocytes was related to the concentration and duration of exposure resulting in large vacuoles in the hepatocytes with pyknotic nuclei. Focal necrosis was also observed in the hepatocytes. The skin showed few atrophying mucous cells, dense inflammatory cells, necrotic epidermis. The weight and length growth occur more in the lower concentrations. The physico-chemical parameters were dose and duration dependent. From this research it was evident that glyphosate had deleterious effects on the fish exposed. Therefore, their use near fish farm or in areas close to aquatic environment should be discouraged or minimized.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background to the Study
Herbicides are widely used all over the world to control the harmful effects of pests and weeds on agricultural productions and fish farm. However, despite the good results of using herbicides in agriculture, their use in the environment is usually accompanied by deleterious environmental and public health effects. The herbicide after being used, ultimately find their way into different aquatic ecosystems and have been found to be highly toxic to non-target organisms, especially aquatic life form and their environment (Nwani et al., 2013).
Herbicides pollution severely affects aquatic organism strophic levels including human beings. The effects of herbicides on fishes are of great concern (Bagheri & Nezami, 2012). Herbicides at high concentration are known to reduce the survival, growth and reproduction of fish and can produce many visible effects on them (Rahman et al. 2002).
Toxicity testing of herbicides on animal has been used for a long time to detect the potential hazards posed by herbicides to man (Rahman et al., 2002). These herbicides and pesticides when applied in restricted areas are washed and carried away by rains and floods to nearby aquatic system, thereby affecting aquatic biota, especially fish, which serves as a rich protein supplement for man (Ndimele et al., 2010; Chattopadhay et al., 2013). The herbicides affect not only the physiology and survival of aquatic organisms but also interact with their genetic make-up leading to mutations and/or carcinogenesis (Goksoyr, 2011; Nwani et al., 2013).
Behaviour is an organism-level effect defined as the action, reaction, or functioning of a system under a set of specific circumstances. We rationalize that a greater understanding of behavioural responses in effect to chemical stress may increase. Therefore, in current scenario there is a need of developing newer and effective methods to study the behavioural responses. Behavioural changes in a fish form an efficient index to measure any alterations in the environmental conditions (Strentiford et al., 2013).
Toxicant exposure often completely eliminates the performance of behaviours that are essential to fitness and survival in natural ecosystems, frequently after exposures of lesser magnitude than those causing significant mortality (Graham, 2004). Environmental factors such as pH, turbidity, alkalinity, dissolved oxygen, temperature and conductivity influence the rate of reaction of the pollutants entering the water or the lethal effects on the aquatic organisms (Fagbenro, 2002). Pollutants in water significantly affect the ability of fish to detect and respond to chemical stimuli, feeding, growth, and reproductive performances could also be seriously affected by such polluted habitat. Pollution of aquatic habitat may result in mass fish mortality or their failure to breed in the polluted environment.
Glyphosate, a broad-spectrum weedicide is one of the most frequently applied pesticides in agriculture for the control of great variety of annual biennial and perennial grasses, sedges, broad leaved weeds and woody shrubs. It is also used for aquatic weed control in fish ponds, lakes, canals and slow running water. Glyphosate is formulated as an isopropylamine salt and can be described as an organophosphorous compound. Glyphosate is described by the manufacturer as pesticide of low toxicity and environmental friendliness. But research has shown that higher concentrations of the product can be toxic, producing a number of physiological changes in organisms and in some cases resulting to death depending on the level, duration and route of exposure. Various concentrations of glyphosate have been shown to be toxic to juveniles of fishes, producing mortality, low survival and various abnormal behavioural changes such as loss of equilibrium status, air gulping, hyper activity, decreased opercula movement, erratic swimming and jerky movements which have been shown to be deleterious to the survival rate of the affected species (Franz et al., 1997).
Haematology is an indicator of immunological status and can provide definitive diagnosis of fish during toxicant exposure (Campbell and Ellis, 2007; Akinrotimi et al. 2010; Nte et al. 2011). Haematological indices are of different sensitivity to various environment factors and chemical (Akinrotimi et al., 2012). Studies have shown that when the water quality is affected by toxicants, any physiological changes will be reflected in values of one or more haematological parameters of aquatic organisms (Akinrotimi et al., 2010; Gabriel et al., 2012). However, Ramesh et al. (2008) noted that there is a possibility that studies on fish blood might reveal conditions within the body of the fish long before there is any outward manifestation of disease. Blood reflects the patho-physiological state of the whole body; therefore, parameters of blood are useful in the diagnosis of the structural and functional status of body organs exposed to toxicants (Felix and Saradhamani, 2015).
Clarias gariepinus is a genus of clariid (order Siluriformes) of the family Clariidae, the air breathing catfish (Goksoyr et al., 2011). It is a popular species in warm water aquaculture and it is indigenous to Africa. It is widely distributed and accepted by many farmers in Africa because of its fast growth, large size, low bone content, tolerance to poor water quality parameters, omnivorous in its feeding habit, adaptability to overcrowding, high market value and has been successfully propagated artificially thereby making its fry and fingerlings easily available (Osman et al., 2006). For sustainable fish production in Nigeria, the ecotoxicology monitoring programmes need to incorporate proper management programmes for herbicide use and disposal in aquatic habitat. This study was therefore aimed to determine if atrazine is toxic to C. gariepinus juveniles.
This fish species has been reported to be most sensitive to aquatic pollutants during their early life stages (Jiraungkoorskul et al., 2003) and the biochemical parameters in fish liver are considered sensitive for detecting potential adverse effects of pollutant damage. Liver micromorphometry has been found to be a reliable biomarker of toxic damage because histological and ultrastructural changes in the cells can be used to predict pollutant stress in acute and chronic concentrations changes in the tissue of individual organisms (Stentiford et al., 2003). The liver is generally regarded as central organ of xenobiotic metabolism in fish and is a target organ affected by toxicant exposure (Mohamed, 2009).
1.2 Statement of Research Problem
Nigerian water bodies suffer from neglect and abuse because of non-enforcement of laws regulating their use. Environmental Impact Assessment (EIA) is not carried out as a prerequisite for the establishment of industries, Ponds are dug indiscriminately even on dunghills that toxic materials has been dumped on for years without any restriction from government agencies. The constant flow of agricultural and industrial effluents into fresh water often leads to a variety of pollutant and accumulation of various metals, which becomes apparent when considering toxic pollution (Martinez, 1991).
These herbicides and pesticides when applied in restricted areas are washed and carried away by rains and floods to nearby aquatic system, thereby affecting aquatic biota, especially fish, which serves as a rich protein supplement for man (Ndimele et al., 2010). The herbicides affect not only the physiology and survival of aquatic organisms but also interact with their genetic make-up leading to mutations and/or carcinogenesis (Nwani et al., 2010). Toxicants contaminate freshwater bodies and affect non-target organisms. Various researchers have reported the effects of chemicals on aquatic organisms (Jiraunghkoorskul et al., 2003). Environmental factors such as pH, turbidity, alkalinity, dissolved oxygen, temperature and conductivity influence the rate of reaction of the pollutants entering the water or the lethal effects on the aquatic organisms (Fagbenro, 2002).
According to a study by (Loper et al., 2002), non-target effects of the herbicide are under increased attention, and injury to non-target plants may increase with the growing use of post emergence herbicides. Suspected physical drift, volatilization, sprayer contamination, over-spray, carry-over of agrochemicals can result in the need for selective use of these agrichemicals. Because most plants are susceptible to glyphosate, endangered plant species are also seriously impacted.
Most environmental problems of concern today are attributed to the production and release of toxic chemicals which are not only capable of interacting with the environment but also disrupting the ecosystem. Indiscriminate discharge of herbicides from agricultural run-off and other sources into aquatic media affects non target organisms such as fish and prawn which are of great economic importance to humans. Toxicants contaminate freshwater bodies and affect non-target organisms. Various researchers have reported on the effects of chemicals on aquatic organisms.
1.3 Justification for the Study
Fish happens to constitute the cheapest source of protein compared to that of livestock as it contains all biological value of all essential amino acids, which are not found in plant protein. Furthermore, fishes are ideal for toxicity test because they are sensitive indicators of chemical pollutants, an important integral part of aquatic communities and can be used as subrogate species for other species acute toxicity.
Glyphosate is chosen for this study because it is used to kill weeds (herbicides), especially annual broad leaves and grasses that compete with commercial crops grown around the globe. As a broad-spectrum herbicide, glyphosate has potent acute effects on most plant species. These include effects on endangered species, reduction in the ability of the plant to fix nitrogen and increased susceptibility to plant diseases. Glyphosate has been described by the manufacturer as a pesticide of “low toxicity and environmental friendliness” (Franz et al., 1997) and as such can seem like a silver bullet when dealing with unwanted vegetation. However, glyphosate has been shown from many studies to pose a variety of health and environmental hazards (Cox, 2000).
1.4 Aim of the Study
The aim of this study is to determine the acute and Sub-lethal toxicities of Glyphosate on the behavior, haematology, histopathology and growth as well as the physico- chemical parameter of tank water of African Catfish Clarias gariepinus juveniles
1.5 Objectives of the Study
The objectives of the study are to determine the:
i. Lethal concentration (LC50) of Glyphosate on juvenile of Clarias gariepinus juveniles.
ii. Behavioral changes of the Clarias gariepinus juveniles exposed to glyphosate.
iii. Haematology of the exposed fishes (Clarias gariepinus juveniles); white blood cell (WBC), red blood cell (RBC), platelets (PTL), haemoglobin (HGB), packed cell volume (PVC), mean corpusular volume (MCV), mean cell haemoglobin (MCH) and mean cell haemoglobin concentration (MCHC) compared with the control.
iv. Histopathology of the (skin and liver) of Clarias gariepinus juveniles exposed to glyphosate of various concentrations compared with the control.
v. Growth rate (standard length and weight) parameters of the Clarias gariepinus exposed to glyphosate compared with the control.
vi. Changes in water quality parameters of tank water of C. gariepinus juveniles exposed to glyphosate
This material content is developed to serve as a GUIDE for students to conduct academic research
TOXIC EFFECTS OF GLYPHOSATE ON THE BEHAVIOUR, HAEMATOLOGY, HISTOPATHOLOGY AND GROWTH OF THE AFRICAN CATFISH, CLARIAS GARIEPINUS (BURCHELL, 1822) JUVENILES
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