HISTOPATHOLOGICAL IMPLICATION OF ZINC OXIDE NANO-PARTICLES ON GILLS AND LIVER OF Heterobranchus longifilis AND AMELIORATIVE POTENTIALS OF ASCORBIC ACID

Zinc Oxide nano-particles (ZnO-NPs) are more useful in the production of commercial goods than other nano-particles because of their unique properties. The effluents of ZnO-NPs get into the aquatic ecosystems and accumulate in fish tissues causing serious health consequences. This study was therefore designed to investigate the toxicity of ZnO-NPs on histopathology of gills of Heterobranchus longifilis. Juveniles H. longifilis were exposed to chronic (6.00, 8.00, 10.00, 12.00 mg/l) concentrations of ZnO-NPs for 60 days. ZnO-NPs-exposed fish were depurated for 30 days to evaluate recovery. Fish were fed on diet supplemented with varying concentrations of ascorbic acid (AA) (50.00, 250.00, 500.00, 1000.00 mg AA/kg diet) for 30 days to ameliorate the toxicity of ZnO-NPs. After each experiment, fish were sacrificed to remove gills and liver for histopathological assay.

Gills of exposed fish revealed different types of histopathological alterations such as epithelial hyperplasia; lamellar fusion; lamellar disorganization; epithelial lifting; disruption of cartilaginous core; epithelial oedema; aneurysms; rupture of epithelial cell and epithelial necrosis. While different alterations such as vacuolation of nucleus, Fatty degeneration, distended Sinusoids with a marked damage in the central vein surrounded by red blood cells, cytoplasmic degeneration, focal fibrosis and necrosis of the cell were recorded in the liver of ZnO-NPs-exposed fish. However, varying degrees of tissue change (DTC) were exhibited in the ZnO-NPs-exposed groups compared to control group, and severity of tissue alterations was concentration-and-time-dependent. The severity of tissue damage increased from slight (13.8 & 15.15) to severe (57.7 & 60.15) in the gills and liver respectively as the concentration and exposure period increased (Figures 1, 4, & Table 2). In depurated groups, the severity of damage gradually recovered from severe (57.7 & 60.15) to slight (19.8) in gills and slight moderate (25.05) in liver after 30 days of depuration (Figures 2, 5 & Table 2), while in the group ameliorated with 500 mg AA/kg diet, the tissue damage were completely reversed (Figures 3, 6 & Table 3) from severe (57.7 & 60.15) to normal (9.3 & 10.3) in both the gills and the liver respectively (Figure 3 & Table 3). The results implied that ZnO-NPs are toxic to H. longifilis and recovery under depuration was slow. However, 500 mg/kg of AA was able to ameliorate the pathological lesions induced by ZnO-NPs.

Keywords: Histopathology, H. longifilis, ZnO-NPs, Depuration, Amelioration, Ascorbic acid