Acute Toxicity of Clarias Gariepinus Fingerlings Exposed to 2,4-D Dimethylamine Salt

This study investigated the acute toxicity of Clariasgariepinusfingerlings. The fingerlings of Clariasgariepinuswere acclimatized for 1 week before the range-finding test was carried out at varying concentrations. Sublethal concentration (viz: 0.00ppm, 10.80 ppm, 18.00 ppm, 25.20 ppm, 32.40 ppm and 39.60 ppm of the 2,4-D Dimethylamine salt) were made in a rectangular aquarium. Each experimental concentration was carried out in triplicate with 10 fish each. The media were renewed at every 24 hours throughout the experimental duration viz: 96 hours. When the fish were introduced into the aquarium containing the toxicants, they exhibited some behavioural changes including opercular movement, air gulping and irregular swimming pattern. The mortality rate significantly increased as the concentration of the 2,4-D Dimethylamine salt increased for each of the exposure duration. The LC50 values at 24, 48, 72 and 96 were 86.15 ppm, 36.28 ppm, 18.72 ppm and 15.68 ppm, respectively. From the findings of this study, there is a need for exercise caution in the use of 2,4-D Dimethylamine salt based herbicides close to the aquatic ecosystem.


Introduction
Pesticides have been found useful in the control of different kind of pest in both homes and agricultural fields [1]. Pesticides are often classified based on the target organisms. For instance, the group of pesticides used to control, mitigate or eradicate pests include insecticides, acaricides, herbicides, fungicides, rodenticides, fumigants. According to Inyang et al. [2], pesticides can also be grouped based on the formulation (soluble in solvent or dust-like), origin (synthetic or organic) and mode of action (contact or systemic).
In recent times, the use of herbicides in controlling weeds in agricultural and home fields have increased. This has raised the concern of many environmentalists, possibly due to the toxicity nature of many herbicides to non-targeted organisms. Herbicides just like other pesticides (such as insecticides, acaricides, etc) tend to cause pollution in the environment depending on the concentrations and exposure duration.
Over a prolonged period, herbicides could cause an alteration in the biochemical and physiological responses of exposed organisms especially fishes in the aquatic ecosystem and small mammals such as rabbits in the terrestrial environment.
Several herbicides have been studied in different parts of the world. But in Nigeria, some of the commonly used herbicides for controlling weeds in agricultural setting include paraquat dichloride [3,4], glyphosate [5] and 2,4-D Dimethylamine salt [6]. Generally, herbicides may find its way into the aquatic ecosystem when they are applied close to surface water resources, and/ or when empty cans of herbicides are discharged into the water bodies directly.
Runoff resulting from precipitation are the major methods through which pesticides enter the aquatic ecosystem [3], where they impact on the water quality and some of the associated fauna and flora.
Fish have been widely used to assess the effect of herbicides such as 2,4-D Dimethylamine salt on surface water resources. Toxicants such as herbicides could cause dysfunction in the reproductive, food conversion efficiency, growth, and mortality rates in fishes [3]. Hence, this study assessed the mortality rate of Clarias gariepinus fingerlings exposed to 2,4-Dimethylamine salt.

Fish Sources and Acclimatization
A total of two hundred and ten Clarias gariepinus fingerlings (mean length of 5.6cm) were procured from a private fish farm in Yenagoa metropolis, Bayelsa state, Nigeria. The fish were acclimatized to an ambient environmental condition in a rectangular aquarium. A sub-lethal concentration of 2,4-D Dimethylamine salt was made and renewed daily. During the process, the fish were fed with their normal coupen fish diet (fish meal).

Range Finding Test (Trial Test)
A renewal bioassay was employed in this study, and the solution of the 2,4-D Dimethylamine salt was renewed daily. A range-finding test of the toxicants was carried out at 10ppm, 25ppm, 40ppm and 55ppm. This  hours. These concentrations were made by using the formula previously described by Inyang et al. [7][8][9][10][11], Aghoghovwia and Izah [4,5], Akinsorotan et al. [12]: mls x stock solution (mg/L) = aquarium water (ml) x desired concentration (ppm or mg/l).

Mortality Determination
The fish was confirmed dead when they did not respond to repeated prodding [3,4], and the percentage mortality was calculated as: Percentage mortality =

Statistical Analysis
Statistical package for social sciences version 20 and graph pad prism 5 was used for the statistical analysis. The data were expressed mean ± standard error, and the charts were plotted using Graph pad prism 5 and Microsoft excel. One way analysis of variance was used to show significant deviations at p=0.05, and Duncan statistics were used to determine the source of observed dissimilarity at p=0.05 The LC 50 values were calculated using Finney  [3,15], Izah [16]. Figure 1 shows the percentage mortality of Clarias gariepinus fingerlings exposed to 2,4-D       [3 -5, 12, 15]. As the acute toxicity duration increases, it could alter the cellular and biochemical processes in fish due to possible changes in enzymatic, haematological, histopathological, physiological and metabolic processes due to hassle and stress.

Conclusion
In recent times, the rate of pesticides use