Haemato-immunological and histological responses in Nile tilapia, Oreochromis niloticus exposed to titanium dioxide nanoparticles.

Abstract

Increased industrial application of nanotechnology has potential to increase nanoparticle contaminations in aquatic ecosystems. However a large knowledge gap exists on influence of nanoparticles on fish populations inhabiting receiving waters. The present study reports the effects of exposure to aquatic suspensions of titanium dioxide nanoparticles (TiO2 NPs, anatase, particle size <25nm: 0, 1, 10 mg l-1, for 7 and 14 days) on some haematological/ innate immune responses and histological structure of gills, liver and intestine of Nile tilapia, an economically important freshwater fish in tropical regions. The results show that TiO2 NPs exposure conditions were not lethal to Nile tilapia but lead to blood parameter alterations and histopathological changes in the organs. Upon exposure of fish to both concentrations of TiO2 NPs for 14 days, erythrocyte counts, haemoglobin levels, total leucocyte counts and percent neutrophils in the peripheral blood were increased significantly (P <0.05) in comparison to the control fish. Despite increases in neutrophils, total phagocytic and myeloperoxidase activities of the blood of fish exposed to 10 mg L-1 TiO2 NPs were depressed significantly (P <0.05) whereas respiratory burst activity was not altered. Serum lysozyme activities in the fish exposed to 10 mg l-1 TiO2 NPs were elevated significantly (P <0.05) compared to the controls. Histological changes seen in the tilapia exposed to TiO2 NPs were epithelial separation, mucous cell proliferation, hyperplasia and lamellae fusion in the gills; hepatocytes with vacuolations, pycnotic nuclei, apoptosis and necrosis in the liver; eroded villi epithelium, reduction of mucous cells and degeneration of mucosa of the intestine. Although blood parameter alterations seen in Nile tilapia can be considered as physiological responses of the fish to cope up with the TiO2 NPs induced stress, observed organ pathologies could lead to serious health implications. Hence, detail studies with a range of environmentally relevant levels are warranted to investigate chronic effects of TiO2 nanoparticles on health of fish populations in the receiving water bodies. We recommend use of Nile tilapia as a tropical fish model for further studies on nanotoxicity.