Pathological investigations in rainbow trout (oncorhynchus mykiss, walbaum 1792) administered with different levels of sodium hypochloride

This study was aimed to investigate pathological findings occured with toxicity of different concentrations of sodium hypochloride used as fishpond disinfectant in rainbow trouts (Oncorhynchus mykiss). Eighty rainbow trout (mean weight of 80 ± 10 g and lenght of 10-12 cm) was used in the study. Eight experimental groups were assigned as; Group I (2 µl/L/day), Group II (5 µl/l), Group III (10 µl/l), Group IV (20 µl/l), Group V (40 µl/l), Group VI (80 µl/l), Group VII (100 µl/l) ve Group VIII (control), each consisting of 10 fishes. Experiment is lasted on day 35 in Groups I, II and III. There was no dead fish observed in Groups I and II in the entire study. Three deaths were recorded on days 33, 34 and 35 in Group III. Seven dead fishes were observed in different periods of study after administration in Group IV. All fishes were died in Groups V, VI and VII at the end of study. Following of necrops of dead or eutanised fishes, all tissues were fixed in 10% neutral buffered formalin solution, embedded in parafin wax, stained by routine methods with haematoxylin and eosin (H&E) examined under the light microscope. There was no significant finding was observed in Group I and II fishes. Decreased feed intake, activity and floating near the surface are clinical signs seen in fishes of other treatments. Macroscobic findings differed according to dose of sodium hypochloride administration. Gills of Goup I, II and III fishes were pale and their surfaces are covered with mucus in different amounts. Petechial hemorrhagies were significant in a few amount of Group II and III fishes. Fishes with pale gills and flake loss were important signs in Group IV. Most significant macroscobic signs were recorded in gills of fishes treated with high dose of sodium hypochloride administration in Groups V, VI and VII. These lesions were as odema, hyperemia and vascular hemorrhage. Microscobic observations in Group I, II and III were hyperplasia and increase in eosinophilic granular cell count, mild degenerations in epidermis. Odema, hyperemia, hemorrhage, necrosis, epitel loss, telangiectasia and hyperplasia were primary microscobic findings in gills of fishes in Group IV. Degenerations in epitelium were recorded in all samples except two of them. All microscobic signs observed in tissues and organs of high dose Groups (V, VI and VII) were showed vascular properties. In conclusion, experimental admission of fishpond desinfectant sodium hypochloride resulted in mild and mid lesions in a dose of 10 µl/l (Grup III) and 20 µl/l (Grup IV). Beside this, this admission had severe (lethal) effects in rainbow trouts with a dose of 40 µl/l and more in the study. Key words: Rainbow trout (Oncorhynchus mykiss), sodium hypochloride, pathological findings.