Abstract: Silicon dioxide is widely used today for different purposes in engineering, biotechnology, medicine and in many daily life products. Large-scale production and use have increased the risk of exposure to silicon dioxide nanoparticles (SiO₂NPs). The present study has focused on the evaluation of this issue by using a nanoparticle, SiO₂NP, in an aquatic model organism, Labidochromis caeruleus larvae. Fish were exposed to SiO₂NPs in three different doses and general histological methods were applied. At the same time, histopathological changes were categorized by semiquantitative scoring. Histological sections of gill, liver, eye and brain tissues were examined under a light microscope after staining with hematoxylin and eosin. Distortion of lamellae shapes in gill tissue, rupture and detachment of primary lamellae, shortening and rupture of secondary lamellae and separation of epithelium were observed. Oedema under the capsule in the liver, pycnotic nucleus in hepatocytes, necrosis in different parts of the parenchyma and large vacuoles were observed. Thinning of the corneal layer in the eye tissue, separation of the lens epithelium and fragmentation of the lens fibres were noted. In the brain tissue, astrocytes were intensely observed in the forebrain, medulla oblongata and spinal cord only in the high dose group. These structural changes are advanced in gill and liver tissues, moderate in the eye, and mild in the brain. These findings reveal that even short-term exposure of fish to SiO₂NPs may pose a potential risk.