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Abstract
The present study was planned to investigate the toxic effect of MG in different concentrations for different periods of exposure on Nile tilapia fish.
Clinical and pathological manifestations, qualitative histopathology and alteration in blood cells were used as parameters for evaluation of the toxic effects.
More over, histopathology was determined quantitatively by mathematical calculation of lesion indices and all the parameters as in the acute and chronic exposure were done.
The ability of MG to accumulate in fish muscle of intoxicated fish were determined by high performance liquid chromatographic method. This had done for acute and chronic exposure.
The results achieved are summarized in the following points:
1. Lethal dose (LC50) assessment of MG in Nile tilapia fish was 0.76 mg/liter.
2. In the acute exposure to MG by dose 0.38 mg/L for seven days, all fish of the intoxicated group show respiratory manifestations, ascitis, exophthalmia and petechial hemorrhages allover body surface.
3. In the chronic exposure to MG by dose 0.076 mg/L for 8 weeks, all fish of the treated group show respiratory manifestations, mild ascitis and petechial hemorrhages allover body surface. Obvious signs were noticed during 3rd -5th weeks then gradually disappeared and fish return normal apparently.
4. The pathological lesions in the acute experiment revealed that:
Gills showed lamellar congestion, separation of epithelium of secondary lamellae, telangiectasis, lamellar necrosis, necrosis of filamentous tips, hyperplasia and EGCs infiltration. Hepatopancreas suffered from congestion with sinusoidal dilatation, fatty and hyDROPic degeneration, necrosis and EGCs infiltration. Posterior kidney showed congestion, necrosis, hyDROPic degeneration, depletion of interstitial haemopoitic tissue and inflammatory cell infiltration. Spleen showed congestion, lymphocytic necrosis and depletion and activation and enlargement of MMCs.
5. The pathological lesions in the chronic experiment revealed that:
Gills showed telangiectasis, hyperplasia with lamellar fusion and necrosis, and inflammatory cells within gill arch. Hepatopancreas suffered from congestion with sinusoidal dilatation and hyDROPic degeneration. Posterior kidney showed congestion, tubular and interstitial necrosis and hyaline DROPlets inside P.C.T. Spleen showed congestion, lymphocytic necrosis and depletion and activation and enlargement of MMCs.
6. Regarding to Quantitative assessments of the microscopical lesions, the most affected organs during acute MG exposure were gills, posterior kidney, hepatopancreas and spleen; respectively. Generally, induced histopathological lesions were time dependant as it gradually increased with exposure time, except spleen which showed gradual increase until the 4th day then become constant.
7. Regarding to Quantitative assessments of the microscopical lesions, the most affected organs during chronic MG exposure were gills then hepatopancreas, while spleen and posterior kidney have same degree of affection. Generally, induced histopathological lesions were gradual ascending till the 5th week then gradually decreased and its high effect noticed during the 3rd- 5th weeks.
8. Determination of some blood parameters in Nile tilapia fish acutely intoxicated with MG revealed a significant decrease in PCV; RBCs; MCHC with a significant decrease in TLC. and during chronic exposure to MG revealed that PCV; RBCs; MCHC; And TLC showed a significant decrease during the 2nd and 4th weeks. While all these blood parameters were not significantly different during the 8th week.
9. Result obtained from the calculation of MG residue in Nile tilapia fish muscle was 16.78 ng/ml during the acute experiment, while during the chronic exposure were (9.38; 10.48 and 10.15ng/ml) in 2nd; 4th and 8th week, respectively and all these results of residue were more than the minimum required performance limit according to European Union.