Abstract:
Crude oil contains genotoxic and carcinogenic substances that can bring
about hazardous effects on organisms at different levels. The objectives of
the present study were to investigate long term effects on growth of juvenile
Oreochromis niloticus fish exposed to crude oil under laboratory conditions,
and to test whether the exposure to crude oil educe any signs of genotoxicity
in the fish, using erythrocyte nuclear abnormalities (ENA) as biomarkers.
Three experimental groups in triplicate were maintained over 90 day period
as freshwater control (N), 5ppm crude oil (T1) in water (V/V%), and 25ppm
crude oil (T2) in water, with addition of 35 live fish into each tank under
semi-static exposure conditions. Fish were sampled (n=20 per tank) at 18
day intervals for growth estimation. Giemsa-stained smears of peripheral
blood and cephalic kidney from each fish (n=6 per group) were prepared on
completion of 90 days, and occurrence of abnormal cells under four different
categories (micronuclei, nuclear buds, fragmented apoptotic nuclei and
altered nuclei) was examined. The results revealed that growth rates in
weight and length, and specific growth rates over 90 day period were
significantly lower in both crude oil exposed groups than in the control group
(p<0.05), indicating a significant growth retardation upon exposure to crude
oil. When compared with control group, there was a significant increase in
the frequency (per 1000 cells) of erythrocyte nuclear abnormalities in fish
exposed to 5 ppm (T1) and 25 ppm (T2) of crude oil. There was a
significantly higher frequency of all ENA types in T2 group compared to T1
group as well. The comparison of the different ENA types between the
peripheral blood and cephalic kidney within each experimental group
showed significantly higher induction of all ENA types except altered nuclei
(AN) in the cephalic kidney in the crude oil exposed groups. In conclusion,
exposure to crude oil caused significant growth retardation and higher
induction of ENA in juvenile O. niloticus.
