الفهرس 
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Abstract
The Studies were conducted using a total number of 180 Oreochromis niloticus with different mean weight 30.0 ± 5.0 g .They were obtained from private fish farm in kafr-Elshike governorate, Egypt and transferred alive to a laboratory of the department of Poultry and Fish diseases - Faculty of Veterinary Medicine- Alexandria University where they were held in aquariums.
Tilapia fish were exposed to Microcystin MC-RR by both of injection intraperitoneally and immersion for 14 days and by feeding with cyanobacterial cells under laboratory conditions for 21 days.
Exposure by injection ( First experiment ):-
Nile tilapia (Oreochromis niloticus) was obtained from a local farm in kafr-Elshike governorate - Egypt and maintained at26 °C for 15 days. They were daily fed with commercial feed, except during the exposure.
Sixty Oreochromis niloticus fish were randomly placed in six aquarium 60-L /capacity containing of dechlorinated tap water under constant aeration. The in vivo exposure period lasted 7th and 14th days at 27 ±1 °C and the fish were intraperitoneally injected to a single dose of crude extract from Microcystis aeruginosa corresponding to MC-RR equivalent 500μg /kg. The treatment exposure groups and the control (control with sterile saline) were performed in triplicate (n=3×10).
At the 7th, 14th days of the exposure period, Oreochromis niloticus were sacrificed, and then stored at −85 °C to await biochemical analysis. Fish mean bodymass was 30.0 ± 5.0 g (Table 1).
Also, during this experiment the recorded parameters were; clinical signs; postmortem changes during different periods. In addition to serum and specimens from gills, liver, kidneys and muscular tissues were collected from different groups to measurement of different antioxidant enzymes namely reduced glutathione (GSH), activities of superoxide dismutase (SOD); catalase (CAT); the level of Lipid peroxidation (Malondialdehyde, MDA); glutathione peroxidase (GPx) and total antioxidant activity (TAC).
Finally Changes in enzyme activities of serum of Aspartate amino transferase; Alanine amino transferase (IU/L); Total protein (mg/dL); Albumin (mg/dL); Creatinine (mg/dL) and percent of Ammonia (%).
Exposure by immersion (Second experiment):-
Nile tilapia (Oreochromis niloticus) was obtained from a local farm in kafr-Elshike governorate, Egypt, and maintained at 26 °C for 15 days. They were daily fed with commercial feed, except during the exposure. Sixty Oreochromis niloticus fish were randomly placed in 6 aquarium 60-L / capacity containing of dechlorinated tap water under constant aeration. The in vivo exposure period lasted 7th and 14th day’s at27 ±1 °C and the fish were immersed in crude extract from Microcystis aeruginosa corresponding to MC-RR equivalent 500 μg / L. The treatment exposure groups and the control (control with sterile saline) were performed in triplicate (n=3×10). At the 7th, 14th days of the exposure period, Oreochromis niloticus were sacrificed, and then stored at −85 °C to await biochemical analysis. Fish mean body mass was 30.0 ± 5.0 g Also, during this experiment the all parameters mentioned in the 1st experiment were recorded.
Exposure by feeding (third experiment):-
Nile tilapia (Oreochromis niloticus) was obtained from a private fish farm in kafr-Elshike governorate, Egypt, and maintained at26 °C for 15 days. Sixty Oreochromis niloticus were randomly placed in 6 aquarium 60-L / capacity containing of dechlorinated tap water under constant aeration. Fishes were fed with commercial fish food plus lyophilized cyanobacterial cells, containing 3500 µg/g MC-RR.
M. aeruginosa cells were fed to the fish by manually crushing mixture of both components (fish food and toxic cells) in a mortar followed by sonication. This procedure resulted in small sticky pellets and was designed to replicate the type of exposure that may occur when a bloom of cyanobacteria under goes lysis under field conditions. It was ensured that all the pellets were eaten within an hour. Also, during this experiment the all parameters mentioned in the 1st experiment were recorded.
1- Results of Clinical examination (Clinical signs and Postmortem (PM) lesions):-
1- a. Results of clinical signs :-
clinical signs of injection experiment :-
No fish died after Intraperitoneal injection or during the exposure periods of 7or14 days. In general visual inspection throughout the experiments revealed that the fish behaved similarly to the control group. Except in some fishes there were discernible differences in swimming behavior, manifested by lethargy, accumulation toward one side of the aquaria as well as stagnation on the bottom of the aquaria. Some fish exhibited abnormal fight/fright response to the stimulus in comparison with control. Moreover, there were some external alterations observed in some fish as slight ascites, slight exophthalmia and pale skin coloration.
clinical signs of immersion experiment :-
No fish died during the exposure periods of 7or14 days. Visual inspection throughout the experiments revealed that some fishes were abnormal slowly swimming behavior, manifested by lethargy, accumulation toward one side of the aquaria as well as stagnation on the bottom of the aquaria. There were some external alterations observed as different stages of eye opaqueness (partial to complete opaqueness), sever bilateral exophthalmia, complete loss of the eye. Some fish showing erythema hemorrhagic patches around the mouth , operculum and pectoral fins, ulcers on the skin and penetrate to the underlying musculature, ulceration at the caudal peduncle and dorsal fin ,Corrosions at dorsal and caudal fin and detached scales.
Histological finding
The skin, muscle, liver and gills of different fish were examined for any histopathological alterations induced by microcystin within the different groups either through supplementation in diet or immersion in water or by experimental injection. Semi-quantitative analysis of the histopathological lesions in muscle, parenchymatous and gills tissue were illustrated in table 1. The lesions were interestingly varied by the route of administration. The musculature and parenchymatous organ degenerative changes were greatly affected with injection rather than the other treatments. Also, the skin lesions were greatly affected in immersion-treated group. Moreover, the immersion of the microcystin induced marked mitogenic effect on the hep