The Impact of Dichlorvos -Pesticide on African Catfish Clarias Gariepinus
Nwamba Helen O*, Achikanu Cosmas E and Chukwu Ginika P
Department of Applied Biology, Enugu State University of Science and Technology, Nigeria
Submission: November 13, 2018; Published: December 05, 2018
*Correspondence author: Nwamba Helen O, Department of Applied Biology, Enugu State University of Science and Technology, Enugu State, Nigeria.
How to cite this article: Nwamba H O, Achikanu C E, Chukwu G P. The Impact of Dichlorvos -Pesticide on African Catfish Clarias Gariepinus. Oceanogr Fish
Open Access J. 2018; 8(4): 555745. DOI: 10.19080/OFOAJ.2018.08.555745
The toxicity of dichlorvos (18 -20 mg/L) on Clarias gariepinus juveniles (mean weight 41.6±1.2(g) and mean length 18.5±2.5 (cm) was investigated in the present study using static bioassays over a period of 96 hours. The determined 96 hours LC50 of the exposed fishes was 17.21mg/L with lower and upper confidence limits of 15.78–18.19mg/L respectively. When the fishes were exposed there was strong evidence of stress responses characterised by hyperactive swimming with subsequent erratic with jerky movements before death which increases with time and concentration of exposure. The quality of water investigated in this study showed no change in dissolved oxygen, pH and temperature. The hepatosomatic indices (HSI) and condition factors (K) which are stress indices due to environmental pollutants decreased within 15 days of exposure and increase in concentration of dichlorvos indicating that it has detrimental effect on the liver of exposed fish with time.
The useful state of water for humans and animals that is appropriate has become a rife concern . There is a rapid decline in the quality of water from natural water resources arising from the demand of industrialisation which employ application of synthetic fertilisers and use of various insecticides and pesticides. Chemicals of agricultural or industrial origins have been reported to be source of contaminations to aquatic ecosystems by runoff and ground leaching through the area . Dichlorvos (2,2- dichlorvinyl dimethyl phosphate) an agricultural insecticide is used to control household pests in public health and protecting crops and stored products. It is reported to be effective against mushroom flies, aphids, spiders, mites, caterpillars, whiteflies in greenhouse, outdoor fruits and vegetable crops . It has contact and stomach insecticidal effect on food and non-food crop pests  and anticholinesterase action associated with the nervous systems of insects [3,5] stated that the volatility of dichlorvos will favour the vaporisation of a significant proportion of applied substance into the external atmosphere which is expected to dissipate rapidly through dilution, degradation and precipitation, reducing the atmospheric (concentrations well below levels. However, aquatic lives run a risk of toxicity if rain falls within 4 hours of application. Increased use of pesticides results in the excess inflow of toxic chemicals, mainly into the aquatic ecosystem [6,7]. This work aims at investigating the effects of dichlorvos on the wellbeing of aquatic organisms particularly on African catfish C. gariepinus. It belongs to the Claridae family and it is geographically located in Africa, the middle east, Brazil and Indonesia. They make fresh water, lakes, rivers and swamps and human made oxidative ponds
and urban sewage system their habitats. The adult catfish can be 1-1.5m in length and weigh up to 60kg with flat body head, broad terminal mouth with four pairs of barbells and large accessory breathing organs made up of modified gill arches .
One hundred juveniles of C. gariepinus were obtained from Rojenny tourist game village, Idemili LGA. Anambra state, Nigeria in 300 litre capacity plastic containers and transported to Heildin fisheries laboratory unit in Enugu state, Nigeria. The mean body weight and the length of the species were 41.6±1.2 (g) and 18.5±2.5 (cm) respectively.
The fish were acclimatised to laboratory conditions for 14 days and fed with top fish feed with crude protein of 38% on daily basis. The container was cleaned, and the water changed every morning. Less than 2% mortality was observed during the acclimatisation.
The preliminary tests to determine the range of concentrations used in this experiment were performed by exposing 10 juvenile catfish to 25 litres of dechlorinated tap water containing 18,20 and 22μl of dichlorvos respectively for 96 hours until suitable concentration that produced 100% mortality was obtained. The fish were not fed for 24 hours before and during the exposure time.
10 juvenile catfish were exposed to different concentrations
of 18, 20 and 22μl dichlorvos in 10 litres of dechlorinated water
from volume to volume (v/v) stock solution (10ml of concentrated
dichlorvos in 1 litre of dechlorinated water) in triplicates. The
mortality rate, behavioural characteristics of the catfish and the
physicochemical properties of water such as pH, temperature, and
dissolve oxygen were analysed every 24 hours for 96hour period
. The 96 hours lethal concentration (LC50) of dichlorvos was
determined following the probity analysis method . Dead
fishes were removed from the experiment pond every morning
to avoid contamination at every 24 hours interval for 96 hours.
Based on the 96 hours LC50 value, the hepatosomatic indices
(HSI) and condition factor (CF) of the Catfishes exposed to two
sub-lethal concentrations of dichlorvos (21 and 43 mg/L) for
15 days were then determined according to White and Flecher
(1985). A set of 10 fish were also maintained in dechlorinated
tap water (0.00mg/l) as the control. The experiment was set in
Using the SPSS statistical package (version 17), the standard
error mean (SEM) and Duncan’s multiple range test were used
to determine the significance at 10% probability test. The
significance between data were analysed with the one-way
analysis of variance (ANOVA).
At the highest concentration of 22mg/L dichlorvos, 87 percent
mortality of juvenile catfish was recorded within the 24 to 96
hours exposure. The least percentage mortality was observed in
in the lowest concentration of 18mg/L. No death was recorded in
the control during the period of exposure (Table1).
The following keys represent; - None, + Mild, ++ Moderate, +++ Strong
The percent mortality increased with increasing concentration.
The behavioural responses of the juvenile catfish exposed to 18,
20 and 22mg/L dichlorvos for 24,48,72 and 96 hours respectively
showed faster swimming, opercula activity, surfacing and gulping of air in almost all concentrations at exposure time compared to
the control. However, at higher concentrations of 20 and 22mg/L,
within 40 minutes of exposure the fish appeared to be hyperactive
and swimming became erratic with jerky movements while at
18mg/L, the fish showed normal behaviour for the first 48hours
then stopped swimming and remained static in response to the
changes in the surrounding environment. There was mean pH
7.1, temperature 27 ⁰C and dissolve oxygen 5.1 for water quality
in various treatments with dichlorvos. The lethal concentration
of dichlorvos that will kill 10-90% (LC10-90) of the experimental
organism at 24, 48, 72 and 96hours was significantly different
(P<0.05). At the exposure period, the median LC50 ranges from
17.21 (15.78-18.19) to 17.98 (16.27-19.35). The hepatosomatic
indices (HSI) with 95% confidence limits showed a significant
difference across the sub-lethal concentrations for day 1 and
15. The condition factor (CF) of C.gariepinus exposed to sublethal
concentrations of dichlorvos was significantly different
throughout the exposure duration compared to control (Table
1-6) (Figure 1).
Values outside the brackets are Lethal Concentrations (LC). First value within the bracket is the lower confidence and the second value is the
upper confidence respectively. Value with different numeric superscripts differ significantly (P<0.05) between different concentrations within the
same exposure duration.
Values with different alphabetic (lower case) superscripts differ
significantly (P < 0.05) between exposure periods within the same
concentration. The values with different numeric superscripts differ
significantly (P<0.05) between different concentrations within the
same exposure duration.
Values with different alphabetic (lowercase) superscripts differ
significantly (P<0.05) between exposure periods within the same
concentration. Value with different numeric superscripts differ
significantly (P<0.05) between different concentrations within the
same exposure duration
The present study is to demonstrate the toxic effects of
dichlorvos in the juveniles of the freshwater fish Clarias gariepinus.
In this study, the survival rate of C. gariepinus decreased as the
concentration of dichlorvos increased. At 96hour exposure to
dichlorvos, the mortality percent for control, 18, 20 and 22mg/L
test samples were 0, 27, 67 and 87 respectively. This finding
agrees with earlier reports by Asuquo et al. Oti, Adakole [11-13].
Toxicity of dichlorvos to organisms has however been shown to
be dependent on concentrations, sex, developmental stages and
exposure periods .
Behaviour provides a unique perspective linking the
physiology and ecology of an organism and its environment and
allows the organism to adjust to external and internal stimuli to
best meet the challenge of surviving in a changing environment
. The results showed that dichlorvos affected the behavioural
characteristics of C. gariepinus. The control specimens were not
hyperactive and showed normal swimming patterns, skin colour,
equilibrium status and fin movements throughout the exposure
period. However, with increasing dichlorvos concentrations and
exposure duration, hyperactivity, air gulping, erratic swimming
and equilibrium instability increased. Besch  reported that
there are contact (high excitability in a moment), exertion (fast
swimming, leaping and attempts to jump out of the toxicant),
equilibrium instability and death phases characterising behavioural
responses of fish to toxicants. Prolonged exposure to dichlorvos
imposed tiredness and stress on the fish suggesting that there is
insufficient intake of oxygen accompanied with detrimental effect
on energy production, body building mechanism and ultimately
nervous breakdown of fish. Heath, Kormakik & Cameron, Kumar
& Krishna Moorthy [17-19] reported deleterious limitations in the
use of energy synthesising macromolecules in fish subjected to
environmental stress. The quality of water for dichlorvos did not
show any significant change in the mean value of pH, temperature
and dissolved oxygen compared to the control. The values fall
within the normal range of water quality for aquaculture . In
this research the 96 hours exposure has 17.21mg/L LC50 values
with lower and upper confidence limits of 15.78 and 18.19
respectively. Ofojekwu et. al.  reported LC50 value of 15.85g/L
for fingerlings of Tilapia zilli exposed to urea fertiliser. Toxicity of
pesticides to organisms is affected by the strains of species, size,
age, sex, temperature, water quality and formulation of the test
chemicals . Fishes are more susceptible to the environmental
variations and respond more to pollutants than mammals. The
fish liver has been shown as a model for studying the relationship
between environmental factors with the hepatic structures and
the functions . Hepatosomatic Index (HSI) and Condition
Factor (CF) gives an indication of the overall health condition
of fish and have been widely used as stress indicator due to
environmental pollutants . In the present study, there was a
significant reduction in HSI and CF on day 15 following exposure
to 21 and 43mg/L compared to day 1 respectively. Jordan et. al.
 reported decreased CF in fish exposed to various toxicants.
The HSI values are generally elevated in vertebrates experiencing
induction of hepatic microsomal P-450 for detoxification of the
pollutants while decline in the HSI and CF may suggest a general
detrimental effect of dichlorvos pesticide on the liver of fish .