Abstract
The present study investigated toxic effects of an agro-pesticide cypermethrin on embryonic and
larval development, haematological parameters, gonadal development and liver of a freshwater
fish Mystus cavasius. Embryonic and larval toxicity were studied by exposing fertilized eggs
(n=100) and newly hatched larvae (n=100) to 0, 2, 4, 8, 16 and 32 µg L-1 concentrations of
cypermethrin in triplicate. The LC50 values (µgL-1) for embryo and larvae were calculated using
probit analysis. The 24-h LC50 for embryo was obtained 5.57 and for larvae 24-h, 48-h and 72-h
LC50 were obtained 9.97, 6.81 and 5.68, respectively. The hatching rates (%) were estimated
75.33±2.52, 64.67±5.03, 45.33±3.21, 38.33±4.16, 28.67±3.21 and 8.33±3.51 for the corresponding
concentrations of cypermethrin. The mortality of larvae significantly increased with increasing
concentrations of cypermethrin. Malformations i.e., damaged germinal ring, edema, egg shell
cracking, cell fragmentation in embryos; and edema, notochord deformity, damaged dorsal and
caudal fin, abnormal body shape in larvae were observed. To examine the effects of
cypermethrin on haematological parameters, gonad and liver, adult male and female of М.
cavasius were exposed to four sub-lethal concentrations of cypermethrin viz. 0, 4, 8 and 16 µgL1 for a period of three months in triplicate. Twenty female and twenty male fish were exposed in
each plastic drum having 100 L of water and followed by monthly sampling. Blood glucose
In levels (mmoIL-1) increased significantly with increasing concentrations of cypermethrin.
female, it ranges from 5±0.59 to 5.53±0.53 in control and 6±0.15 to 10.13±0.53 in treatments, and in
male, it ranges from 4.9±0.25 to 5.3±0.57 in control and 5.73±0.14 to 9.6±0.47 in treatments. Blood
Hb levels (gdL-1) dropped significantly with increasing concentrations of cypermethrin.
female, it ranged from 8.6±0.34 to 9.5±0.59 in control and 4.6±0.31 to 7.86±0.29 in treatments, and
in male, it ranged from 9.06±0.43 to 9.8±0.75 in control and 4.8±0.41 to 8.2±0.30 in treatments.
In
RBC counts dropped significantly with increasing concentrations of cypermethrin. In females,
the RBC values (10'mm-3) ranged from 2.03±0.36 to 3.27±0.03 in control and 0.59±0.06 to 1.88±0.95
in treatments. In males, it ranged from 2.48±0.014 to 2.61±0.06 in control and 0.38±0.03 and
1.88±0.36 in treatments. WBC counts were elevated in most of the fishes exposed to
cypermethrin. In female, the WBC values (103mm-3) ranged from 34.4±10.2 to 36.8±15.8 in control
and 41.5±3.3 to 58.3±23 in treatments, and in males, it ranged from 37.7±6.1 to 44.3±14.9 in
control and 44.5±27.5 to 71.65±7.9 in treatments. To examine the effects of cypermethrin on
gonads, fishes were sacrificed on 30, 60 and 90 days of exposure. There were no significant
differences in gonadosomatic index values of control and treatment. However, histopathological
changes were observed in both ovary and testes histo-sections. In ovary, deformities observed
were wrinkle oocyte, cytoplasmic clumping, atretic follicle, degenerated granulose layer,
degenerated oocyte wall, increased inter follicular space, adhesion, cyst, necrosis, etc. In testes,
deformities observed were break down of tubular epithelium and focal loss of spermatocytes,
increase in the interstitial area, dilation of the lumen, sertoli cells degeneration, spermatozoa
mixed with the cells wall and structures like early primary spermatocytes in the lumen and
elongated seminiferous tubules, etc. In both ovary and testes, intensities and occurrences of
deformities were higher with increasing concentrations and durations of exposure.
Histopathological changes in liver were also studied and pyknosis of hepatocytes, mild to severe
necrosis, haemorrhage, degeneration of muscle and vacuums were identified as notable
pathologies. Hepatosomatic index showed higher values for treatments compared with control.
Mean values of water quality parameters viz. pH, temperature, dissolved oxygen and alkalinity
did not differ significantly between treatments and control. The findings of this study suggest
that agro-pesticide cypermethrin, at very low concentrations, is capable of adversely affecting
development of embryo and larvae, haematological parameters, liver functions and gonadal
development of a freshwater fish M. cavasius.