The authors have declared that no competing interests exist.
This study evaluated the behavioural response and toxicity of paraquat dichloride to fingerlings of
In the recent times environmental resources (soil, water and ambient air quality) are threatened due to pollution resulting from anthropogenic activities
Instances of substances recalcitrant to degradation (such as heavy metals) has been reported in surface water system in the Niger Delta
Pesticides are substances that are used for controlling pest in homes and agricultural field. In the recent times, pesticides use is on the increasing trend. As such, pesticides are among the important pollutants of the aquatic ecosystem. Despite their roles in controlling pests in the environment, many of them pose a great problem to the environment probably due to their toxicity to animals and human. Their toxicity level depends on their chemical compositions and as well as the immune system and other metabolic pathways of the target organisms.
Paraquat, a non-selective, quaternary nitrogen based herbicide is use in controlling weeds
The remains of cans of herbicides if not properly discarded could end up in the water ecosystem especially in coastal region where most of their municipal waste are dumped in aquatic ecosystem/ and or close to surface water resources. In addition, after rainfall, runoff could wash herbicides used in agricultural field close to surface water resources were they could impact on the receiving water quality.
Fish are sensitive to aquatic pollutants, and as such they have been widely used to ascertain the effects of contaminants on aquatic ecosystem. Many herbicides have the tendency to cause dysfunctioning in the reproductive, food conversion efficiency, growth and mortality rates in fishes. Fishes have been widely used as bio-indicator in assessing pollution level in aquatic ecosystem. Hence this study focused on the behavioural response and acute toxicity of
Two hundred fingerlings of
A static renewal bioassay technique was employed in this experiment. During the process, the test toxicant (paraquat dichloride) and test solution (water) were renewed daily. A range finding test (trial test) was carried out using the toxicant in the following concentrations (15ppm, 25ppm, 35ppm and 45ppm) to determine a safe sub-lethal concentration for the main experimental run. Each of these concentrations contains 4 fishes each.
A 0.00 mls (control) 0.6mls, 0.8mls, 1.0mls, 1.2 mls and 1.4mls of paraquat dichloride (276g/L) (equivalent to 276000 mg/L) was pipetted into rectangular aquarium containing 10 litres of water (equivalent to 10000 mg/L). This brings the concentration to 0.00ppm (control), 16.56ppm, 22.08ppm, 27.60ppm, 33.12ppm and 38.64ppm for
Mortality was established when they failed to respond to repeated prodding
Mortality rate =
The behavioral changes were determined by physical observation of the fishes at different concentration of the paraquat dichloride. The behavioural response of the fish was assessed based on the features presented by Inyang
The in-situ water quality parameters analyzed include pH, temperature, conductivity and salinity. All the in-situ characteristics were carried out following manufacturers guide. The pH, conductivity and salinity were determined using in–situ portable pH meter. The calibrated pH conductivity and salinity meter electrode was then dipped in water samples, and the readings were taken when the values that displayed in the meters were stable. While the temperature was measured using thermometer.
The statistical analysis was carried out using Statistical package for social sciences version 20. The data were expressed as mean ± standard error, and one-way analysis of variance was used to show significant variations at p=0.05. Waller Duncan statistics was used to ascertain the source of variations at p=0.05. The percentage mortality was transformed to probit using Finney’s table
The water quality characteristics of the aquarium for the various concentrations are presented in
Parameters | Concentration, ppm for |
|||||
0.00 | 16.56 | 22.08 | 27.6 | 33.12 | 38.64 | |
pH | 6.4 | 6.8 | 6.7 | 6.6 | 6.5 | 6.4 |
Temperature, ºC | 25.0 | 25.0 | 25.0 | 26.0 | 26.0 | 27.0 |
Conductivity, µS/cm | 63.2 | 86.5 | 94.9 | 92.4 | 109.6 | 131.5 |
Salinity, ‰ | 0.02 | 0.03 | 0.03 | 0.04 | 0.03 | 0.00 |
The Behavioral response of
The percentage mortality of varying concentration of paraquat dichloride exposed to the fingerlings of
Concentration , ppm | 24, hours | 48, hours | 72, hours | 96, hours |
0.00 | 0.00±0.00a | 0.00±0.00a | 0.00±0.00a | 00.00±0.00a |
16.56 | 10.00±0.00ab | 13.33±3.33ab | 20.00±0.00b | 23.33±3.33b |
22.08 | 13.33±3.33b | 20.00±5.77b | 26.67±3.33bc | 43.33±3.33cd |
27.60 | 16.67±3.33bc | 23.33±5.77bc | 33.33±5.77c | 50.00±5.77d |
33.12 | 20.00±5.77bc | 26.67±3.33bc | 36.67±3.33cd | 56.67±3.33e |
38.64 | 26.67±3.33c | 36.67±3.33c | 46.67±3.33d | 76.67±3.33 |
Data is expressed as mean ± standard error. Different letters indicate significant difference at p<0.05 according to Waller Duncan statistics
Presents LC50 values of fingerlings of Clarias gariepinus exposed to paraquat dichloride. The LC50 values at 24, 48, 72 and 96 were 59.95, 47.59, 38.12 and 26.18ppm, respectively (
This study demonstrated that herbicides such as paraquat dichloride are toxic to fingerlings of