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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. |