Mortality Rate of Clarias gariepinus Fingerlings Exposed to 2, 3- dichlorovinyl dimethyl Phosphate

2, 3- dichlorovinyl dimethyl phosphate is an organophosphate insecticide used in the control of insects in both agricultural and household. This study investigated the mortality rate of Clarias gariepinus fingerlings exposed to 2, 3- dichlorovinyl dimethyl phosphate. Samples Clarias gariepinus were bought from a private fish farm in Yenagoa metropolis, Nigeria. The fishes were acclimatized in the laboratory for 3 days. A static renewal bioassay methodology was adopted. Results showed mortality rate of 32.85, 57.14 and 72.86% at 0.20, 0.60 and 1.00 ppm respectively (based on different concentration) and 32.67, 43.33, 56.67 and 73.33% respectively at intervals of 12, 24, 48 and 96 hours (based on time). There was significance difference (P<0.05) with respect to concentration, time and interaction of time/concentration. Results also showed increased mortality with increased concentration and exposure duration. The results showed that even at low concentration, 2, 3- dichlorovinyl dimethyl phosphate could still induce mortality in fingerlings of Clarias gariepinus. As such caution should be exercised in the use and disposal of empty cans of 2, 3- dichlorovinyl dimethyl phosphate close to aquatic-systems.


INTRODUCTION
Water is one of the unique resources required for the growth, development and survival of living organisms [1][2][3][4][5][6]. Water resources are majorly contaminated by human activities and to a lesser extent by natural phenomena [7]. Beside portability and domestic utilization especially by humans, water is also habitat to several aquatic life forms including fishes (fin and shelled fishes). Fish is a major source of animal protein. The harvesting of fishes in the wild (fishing) is a major source of livelihood to indigenous people especially in Bayelsa state, Nigeria. Industrialization and urbanization has led to constant degradation of the environment (soil, air and water) resulting in eutrophication and loss of biodiversity.
Surface water abounds in Nigeria. According to Izah and Srivastav [4], over 10 out of the 36 states are named after water bodies. Nigeria as a nation is divided into three by rivers. Several rivers, creeks and lakes are named after a town. According to Olopade et al. [8], several communities and towns lie in the watershed of the Niger River, and other major river systems include the Benue River, Cross River, Anambra River, Imo River, Kwa Iboe River, Ogun River and Oshun River. Majority of these rivers has tributaries.
Specifically, in the Niger Delta, freshwater, brackish and marine water are found in the region. The sizes of the water differ and are called by several names including lake, pond, creek, creeklets, stream, rivulets, river etc. The water resources are major receipt of wastes generated by several sectort including household and industry. Some notable pollutants aquatic resources emanates from erosion, siltation, domestic and industrial wastes, effluent from abattoir, motor garages, mechanical shops, excreta disposal, agricultural activities as well as bathing and washing [8]. These wastes are discharged into the water directly and indirectly (via runoff after rainfall). In river line communities in the Niger Delta specifically Bayelsa state, several wastes streams are discharged into the aquatic ecosystem including sewage via pit toilet system [2,6,9,10], food processing wastes such as oil palm mill effluents [11], household and market solid wastes. The activities leading to changes in water quality parameters could also affect the composition and abundance of life in such water medium.
In recent times, synthetic pesticides are used for the eradication of weed (herbicides), insects (insecticides), ticks (acaricides) etc. Typically, pesticides are substances used to control pest (in order to protect crop and preserve materials, eradicate weeds, control disease transmitting vectors/organisms) [12][13][14]. Most toxic pesticides are harmful to non-target organisms.
In coastal region especially in the Niger Delta, the use of insecticides containing 2, 2-Dichlorovinyl Dimethyl Phosphate has increased. Ajiboso et al. [15] reported that 2, 2-dichlorovinyl dimethyl phosphate is one of the commonly produced and utilized insecticides in Nigeria with effectiveness and potency compared to other competitive household insecticides (including mosquito coil and flints).
2,3dichlorovinyl dimethyl phosphate is one of the pesticides that belong to the organophosphates group of insecticides. 2, 3-dichlorovinyl dimethyl phosphate is sometimes called dichlovos [16,17]. It is one of the broad spectrum insecticides used in the control of household, and stored products insects [16,17]. According to Ashade et al. [16], the toxicity of the organophosphate is due to their ability to inhibit cholinesterase enzyme which results in the accumulation of acetycholine in nerve tissues of the effector organs. Organo-phosphates are broader in insecticidal spectrum.
Handling and use of insecticides containing 2,3dichlorovinyl dimethyl phosphate is indiscriminate. Generally, the discharge of empty cans of pesticides could be harmful to the environment. This is because the remains in the cans could be toxic to aquatic ecosystem especially fishes when they are leached into the nearby surface water due to soil erosion [18][19][20][21][22][23][24][25]. Furthermore, Babatunde and Oladimeji [26] reported that pesticides usually get into the aquatic environment through accidents or through run offs from surrounding farmlands and leads to mortality and morbidity in aquaticsystem such as fisheries. Therefore, this study is designed to assess mortality rate of Juvenile Clarias gariepinus exposed to 2, 3dichlorovinyl dimethyl phosphate.

Source of Fish, Transportation and Acclimation
Clarias gariepinus fingerlings were purchased from a private fish farm in Yenagoa metropolis, Bayelsa state. The fish samples were transported to the laboratory in 20 liter rubber cans covered with fishing net. The fish was allowed to acclimatize in circular rubber aquaria for 3 days. During which they were fed with normal coupen fish diet (fish meal) at 5% body weight for week. A static renewal bioassay was employed for the study.

Range finding and Main Test
The toxicant was prepared into lower concentrations from manufacturer stock of 1000 g/l.

Statistical Analysis
Statistical package for social sciences software was used for the statistical analysis. Two way analysis of variance was carried at P=0.05 and Duncan multiple range test statistics was used for mean separation.

RESULTS AND DISCUSSION
The mortality rate of Clarias gariepinus fingerlings exposed to different concentration of 2, 3 dichlorovinyl dimethyl phosphates is presented in Fig. 1. Mortality rate of 32.85, 57.14 and 72.86% was attained at 0.20, 0.60 and 1.00 ppm respectively. The concentration of the toxicant that could cause 50% mortality in the fish is 0.41 ppm. Furthermore, mortality rate of the Clarias gariepinus fingerlings exposed to 2, 3-dichlorovinyl dimethyl phosphate at varying time interval is presented in Fig. 2  Typically as the concentration of the toxicant increased the mortality rate also increases. Furthermore, the increased exposure to the toxicant also affected the mortality rate. The results of this study showed that 2, 3dichlorovinyl dimethyl phosphate is highly toxic to fingerlings of Clarias gariepinus even at low concentration. The absorption of 2, 3dichlorovinyl dimethyl phosphate by the gills and/or intestinal epithelium of the fish could have led to imbalance in osmo-regulatory ability of the fish. This could have probably led to impairment in histology, histopathology, haematology, electrolytes, metabolites and enzymatic characteristics of the fishes. Due to the role of tissues and organs in metabolism and physiology in fisheries, any dyfunctioning could be highly lethal to their survival. Authors have reported that 2, 3-dichlorovinyl dimethyl phosphate is toxic [15 -17]. Ashade et al.
[16] also reported that 2,3dichlorovinyl dimethyl phosphate is highly lethal to fingerlings and affect behavioral response.
Clarias gariepinus is one the Niger Delta common wetland fish [35,36] that could thrive in both well and poorly oxygenated water [12,37]. therefore, the impart on this species of fish suggest that 2,3 dichlorovinyl dimethyl phosphate could have adverse effect on other fish species found in Niger Delta inland water ways.

CONCLUSION
2, 3-dichlorovinyl dimethyl phosphate containing insecticides is one of the mostly widely used insecticides in the Nigeria Delta region of Nigeria. The remains of disused cans are frequently discarded alongside with other household and domestic wastes into the environment without any form of treatment. This study evaluated the toxicity of 2, 3-dichlorovinyl dimethyl phosphate in fingerlings of Clarias gariepinus, a common Niger Delta wetland fish. The study found that 2, 3-dichlorovinyl dimethyl phosphate is highly toxic to fingerlings even at low concentration. Therefore, care should be taken during the use and discarded of empty cans of 2, 3dichlorovinyl dimethyl phosphate especially close to aquatic ecosystem.