Histopathological study of parasitic infestation of skin and gill on Oscar (Astronotus ocellatus) and discus (Symphysodon discus)

Histopathology provides a rapid method to detect effects of irritants and pathogens in different organs and it can be considered as the indicator for abnormal condition for fish environment. The present study was initiated to record the histopathological lesions of gill and skin associated with external parasites in two common aquarium fish, Oscar (Astronotus ocellatus) and Discus (Symphysodon discus) fish. Twenty Oscar and twenty Discus were obtained from aquarium shops and wet mount was prepared from skin and gill mucosa and histopathological study was performed on tissue samples of gills and skin on tissue sections which were stained with haematoxilin-eosin. Based on the results, Dactylogyrus sp. was the most prevalent parasites in Oscar and Discus fish. Ichthyophthirius multifliis, Trichodina sp. and Gyrodactylus sp., Epistylis sp. and Vorticella sp. were seen in the skin and gill of fish. In histopathological examination, fusion of secondary lamella associated with hyperplasia, aneurysm, edema, purulent bronchitis were seen. Sections of Ichthyobodo sp. and purulent bronchitis are rare and in skin. Dermatitis was observed. Histopathological lesions in Oscar were in high rate in comparison with lesions which were seen in Discus and they are in relation to parasitic infestation.