Indian Journal of Experimental Biology Vol. 37, February 1999,
pp. 166-168
Effect of endosulfan on oxygen equilibrium curves of blood of
food fish Oreochromis mossambicus (Peters)
C Rangaswamy* & B Padmanabha Naidu
Department of Zoology, Sri Venkateswara University, Tirupati
517502, India
Received 14 August 1997; revised 7 October 1998
Oxygen equi librium curves of the blood of the control
o.mossambicus was sigmoid and Pso and ' n' va lues were 12. 5 mm Hg
and 3.57 respectively: Upon exposure to sub-lethal and lethal
concentrations of endosulfan the oxygen equilibrium curves of the
blood moved to the right. Thus, the P50 value in the treated fi sh
tended to increase signifying the reduction in the affinity of the
pigment for oxygen . A decrease in blood p H due to increase in CO2
content was noticed . Th is caused in-crease in Pso and consequent
shifting of oxygen equilibrium curves to the right in the
endosulfan treated fish and showed the existence of normal or
negative Bohr effect. Thus endosulfan exposure causes not only the
direct harmful effects on the fish , but also the indirect effect
on gas exchange property of blood.
Endosulfan (C9H6CI60 3S) a broad spectrum cyclodiene pesticide
is widely used in agriculture for the control of pests of food
crops. These pesticides cause mass mortality of fish and other
non-target aquatic organisms l-3. Respiratory properties of
haemoglobin is well known 4-10. However, the effects of pesticide
contamination on the oxygen equilibrium curves of the fish blood is
not well described . The present study reports the effects of
lethal and sub-lethal concentrations of endosulfan toxicity on the
oxygen equi librium curves of the blood of Oreochromis
mossambicus
Materials and Methods
Live fi sh ( 10 ± 2 g) were collected from the loca l ponds
around Tirupati and were acclimated to laboratory conditions.
Static bio-assay experiments indicated the LCso value to be 2.78
Ilg/L for endosulfan for the spec ies. Fish were exposed to lethal
(LCso/96 hr) and a sub-lethal ( lj. of LCsof96 hr for 24,72, 120
and 240 hr) concentrations of endosul fan to evaluate their
toxicity on oxygen equil ibrium curves of the blood. Bio-assay of
controls were also performed. The experiments were conducted in 50
L aq uari a containing fresh water. The water quality parameters of
the experimental aquaria were recorded to be: temperature 26±2°C;
pH: 7.4-7.6 ; dissolved oxygen: 7.8-8.0 ppm and salinity; 0.191 gi
L. .
B iood was collected from the ventricle using EDT A as
anti-coae.ulant. The preparation of haemoglob in was carried out as
s~ggested by Manwe ll ll - 13 The different spectra of
oxy-haemoglobin were determined in the vis ible range
• Present Address: Central Institut e or fS rilckishwaler
Aquacullure Chennai 600 008, India
using deoxygenated blood as blank. pH of the blood of control
and endosulfan exposed fi sh were recorded_
Oxygen equilibrium curves of the haemoglobin were determined at
26 ± 1°C and 575 nm (the peak of maximum absorption) using a
Spectrophotometric method with certain modifications 14. 15.
Haemoglobin (3ml) solution was taken for the determinations . Five
separate samples of blood of the control fish and that exposed to
sub-lethal and lethal concentrations of endosulfan were collected
for the determination of oxygen equilibrium curves and other
parameters. The oxygen equilibrium curves were drawn by plotting
the values of percent oxy-haemoglobin (Y) against the partial
pressure of oxygen (P02) . The values of ' n' (Hill's Coefficient)
at Pso were determined from the slope of the curve obtained by
plotting log Y 1100-Y against Log P02. The values of . n' related
to other va lues of Y were also calculated.
Results and Discussion
The relation between the oxygen tension and the percentage
saturation of haemoglob in of the blood of contro l and endosulfan
exposed fish at sub-lethal and letha l concentrations are
represanted in Fig. I . The oxygen equi librium of the blood of the
contro l fish depicted a sigmoid curve indicating the positive inte
raction among the oxygen combining sites of the haemoglobin .
Sigmoid oxygen equil ibrium curves have been reported in trout and
mackerel9 The P50 va lue for the control fish is 12.5 111m Hg. The
Pso value varies from species to spec ies. In the catfish,
Saccobranchus fossilis and Clarias batrachus Pso of the blood was
reported to be 6.7 and 16.2 mm I-I g respectivel/ 6. 17 ,
Sub-lethal and lethal concentrations of endosulfan induced a
gradual increase in the P50 and Pqs va lues (F igs. I and 2) and
shi fting of the oxygen equilibrium curves towards the right, which
is due to the
RANGASW AMY & NAlDU : EFFECT OF ENDOSULF AN ON BLOOD OF
OREOCHROMIS MOSSAMBICUS 167
inability of the pigment to extract more oxygen trom water under
toxicity stress. The P 50 values for 24,72,120 and 240 hr
sub-lethal and 96 hr lethal exposures of endosulfan were 14.0,
15.5, 16.0, 17.5 and 18.5 mm Hg (Table I) indicating that the
affinity of the pigment for oxygen is reduced upon exposure to
endosulfan. It is for this reason that the oxygen equilibrium
curves of endosulfan exposed fish are shifted to the right of the
control fish.
Endosulfan toxicity induced certain behavioural changes such as
restlessness, muscular spasm with jerky and violent movements in
the fish . A reduCtion in the opercular movements was observed. The
rate of ventilation was perhaps inadequate for the rate of CO2
production. A reduction in the oxygen consumption of the fish was
also recorded under the pesticide stress. Thus, an overall decline
in the physical ability of the fish was recorded under endosulfan
toxicity.
FIG .
100
80
z Q ~
« 60 a: ;:) ~
« Vl
I-Z lJJ U
40 a: lJJ Q.
F I G.
C7' 20 I
20 E E
~ 10 Q.
The values of ' n' at P 50 for the contro l and fish exposed to
24,72, 120 and 240 hr sub-lethal and 96 hr lethal concentrations of
endosulfan were found to be 3.57, 3.41 , 3.24,3.21,3.19 and 3. 14
respectively (Table I) . The values of ' n' at other percentage
saturation of the pigment are shown in Fig.3, which indicated that
the degree of interaction of the oxygen combining sites in control
fish increases upon progressive oxygenation . Majority of the
oxygen equi librium curves are more or less sigmoid and the ' n'
values are greater than I . The ' n' va lue for the catfish,
Saccabranchus fassilis and clarias batrachus were determined to be
1.13 and 2.0 while that of Ictalurus nebulas us varied trom 1.22 to
2.22 (ref. 9, 17, 19). The high 'n' value reported for the control
fish indicated greater interaction amongst the oxygen combining
sites of the haemoglobin molecule. However, in the endosulfan
exposed fish the ' n' values are less than that of the control
2
l Sl _.
C 24. 72 96 120 24.0
EXPOSURE PERIOD (hrs)
10 20 30 40
P02 (mm Hg)
Fig. I--Oxygcn cquilibrium curvcs o f the blood of contro l and
cndosu lfan cxposed 0. mossamhiclis Fi g.2- Efrcct of sub-kthal and
k thnl concenlrations of en do sui fan on the hal f saturation
tension (Pso) ofo.mossamhiclIs.
