The impact of natural co-infection of dactylogyrus spp. and aeromonas hydrophila on behavioural, clinical, and histopathological changes of striped catfish, pangasianodon hypophthalmus (sauvage, 1878): a case study

Abstract

The present case study reported the effects of Dactytlogyrus spp. infection on cultured striped catfish, Pangasianodon hypophthalmus. The clinical signs, gross, and histopathological changes inflicted by the parasite on the gills, liver, spleen, and kidney were examined. The fish were sampled from Aquaculture Research Station of Universiti Putra Malaysia, Puchong, Selangor. P. hypophthalmus infected with Dactylogyrus spp. exhibited several clinical signs, including lethargy, unilateral swimming and sluggish movement on the water surface. Post-mortem examination revealed the congestion of the swim bladder and haemorrhages of the external organs. Examination on the gill indicated hypertrophy and hyperplasia, proliferation of epithelial cells and fusion of the secondary lamellas. The liver sections exhibited severe haemorrhages, vacuolation and congestion of the hepatic vein. Haemorrhages were observed in the kidneys; other lesions were rupture of renal tubules and aggregation of lymphocytes in almost all of the organs examined. Bacteriological examination of the moribund fish revealed secondary infection with bacteria, Aeromonas hydrophila. The findings revealed that the damage to the gills could be related to the respiratory impairment caused by Dactylogyrus spp., while the external injuries may serve as the point of entry for bacteria, making the fish vulnerable to A. hydrophila infection that subsequently resulted to mortality.