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Abstract
In the present study 480 specimens of Oreochromis niloticus
were used to determine the adverse effects of different sublethal
concentrations of lead (2.5, 5 and 10 ppm) on behavioral changes,
mortality, growth performance (body weight gain, condition factor
and hepatosomatic index), blood constituents (hemoglobin, glucose,
total protein, albumen, globulin, lipids, trieglycerides, ALT and AST
enzymes) and histopathological characteristics of the liver. The
validity of selenium (0.5 and 1.0 mg) and vitamin E for inhibition of
such effects was testified.
The results can be summarized in the following points:
1- After 21 days of treatment, lead exposed fish showed abnormal
behavior such as nervous manifestation, change in color and fins
stretching. Fishes treated with vitamin E and first dose of
selenium were in better conditions.
2- The individual selenium and vitamin E doses and their
interaction improve fish growth. Higher doses of lead and their
interaction with selenium doses exhibited negative effect on body
weight gains.
3- The condition factor and hepatosomatic indeces of treated
O. niloticus exhibited variations in their values.
Blood constituents: 4- Hemoglobin level was significantly affected by lead doses
and time of exposure. Hemoglobin level increased with addition of
selenium.
5- Glucose level decreased during the second and third weeks
but increased in the fourth week. With increase of lead doses the
glucose level was gradually decreased.
6- Total protein level decreased through the second week and
increased through the third and fourth weeks. wherease, such level
decreased with the increase of lead doses.
7- The albumin level through weeks was fluctuated toward
increase and decrease whereas the main effect of lead was postulated
toward the decrease of albumin level with increase of lead doses.
8- The globulin level decreased through the second and third
weeks then increased in the fourth week. The lead main effect showed
decreased level of globulin with increase of lead doses.
9- A/G ratio was high through the third week then decreased in
the fourth week. Fluctuation of A/G ratio was recorded with increase
of lead doses.
10- The total lipid decreased in the second week, then
increased up to the fourth week. The lead main effect exhibited
fluctuation in lipid level among its increased doses. The selenium and
vitamin E had no significant effect on lipid levels.
11- As regards the trieglycerides level, the lead main effect
was differential among weeks and showed decreased overall trend.
The selenium and vitamin E exhibited insignificant effects.
12- ALT and AST levels decreased through the second and
third weeks then increased in the fourth week. The lead main effect
revealed decreased levels of ALT and AST with increase of lead
doses.
Histopathology
The study included light and electron microscopic detailed
descriptions of the histopothological and cytopthological
characteristics of the liver of fish Oreochromis niloticus in the normal
condition and after exposure to different doses of lead nitrate,
selenium, vitamin E and their combinations for 7,14, 21 and 28 days
Light microscopic changes
Treatment with (2.5, 5,10 ppm) lead nitrate for 7, 14, 21 and
28 days showed histopathological changes and as the duration of the
experiment increased, the alterations become more poronounced:
* Dilatations of blood vessels which often conjested with blood
cells.
* Cytoplasmic vacuolation with densely stained nuclei.
* Proliferation of connective tissue fibres.
* Presence of lipid DROPlets in the cytoplasm of hepatocytes were
pronounced after exposure to high dose.
* Presence of necrotic areas and the appearance of patches of
haemorrhage.
* Increased of melanomacrophage center.
* Marked glycogen depletion in all exprimental groups.
The most characteristic changes in the liver of fish exposed to
selenium (0.5 , 1.0 mg/kg) for 7, 14, 21 and 28 days are:
Marked increase in lipid DROPlet in the hepatocytes.
* Severe vascular congestion.
* Infiltration of lymphocytes.
* Degeneration of most liver cells.
Histological examination of the liver revealed the following
changes in fish treated with selenium plus lead (0.5 mg selenium plus
2.5 ppm lead, 0.5 mg selenium plus 10 ppm lead nitrate).
The hepatocytes appear in different stages of degeneration, swelling
and vacuolation.
* Vascular conjestion and degeneration of most liver cells.
* The presence of macrophages with increased stainability and
surrounded by lymphocytes.
No histopathological changes were observed between
specimens that have been supplemented with vitamin E and those,
which have not been supplemented.
Ultrastructural changes
Ultrastructural examination of the liver revealed the following
changes in treated fish (5ppm, 10 ppm lead ) as compared to control.
* Transformation of the rough endoplasmic reticulum into
concentric arrays.
* Dilated rough endoplasmic cisternae were often filled with
dense material.
* Increased amount of lysosoumes of varying densities and sizes. *
Proliferation of smooth endoplasmic reticulum.
* Increased variability in mitochondria.
* Decreased in the amount of nuclear hetrochromatin.
* Increased lipid DROPlets of varying sizes and densities.
* Fragmentation of the rough endoplasmic reticulum after the high
dose.
Many ultrastructural alterations were observed in fish
following exposure to 0.5 mg/kg selenium:
* Disarrangement of the rough endoplasmic reticulum.
Reduction in the amount of mitochondria.
* Swollen of mitochondria with destructed cristae.
* In other nepatocytes, mitochondial clumping at one side leaving
wide areas of harified hyaloplasm
The ultrastructaral changes in the liver of fish exposed to 0.5
mg selenium plus 2.5 ppm lead are :
* Swelling of hepatocytes with large rarefied areas in the cytoplasm
resulting in dissociation of organelles.
* Severely affected hepatocytes seemed to be swapped from their
cytoplasmic organelles and large lipid DROPlets occupied most of their
cytoplasm.
* Heterochromatin clumping in the nucleus and large vacuolated
spaces in the cytoplasm.