Microplastics induced histopathological lesions in some tissues of tilapia (Oreochromis niloticus) early juveniles

Although microplastics (MPs) have received increasing focus and currently have become an emerging area of research, there is limited knowledge about their effect on whole body histology of fish. In this study, tilapia (Oreochromis niloticus) early juveniles were exposed to 1, 10, or 100 mg/L of MPs for 15 days and 15 days post-exposure, after which whole body histological examinations were performed. Histological analysis of kidney revealed congestion of blood capillaries, inflammatory cells, loss of basophilic cytoplasm in several tubules, vacuolated tubules, shrinking of convoluted tubules, widening of intertubular space, complete deformation, glomerular atrophy, vacuolated glomerular cells, and signs of fatty tubules. The liver tissue exhibited vacuoles, hydropic degeneration, necrotic area, severe deformation of hepatocytes, pyknotic nuclei, and dilation and congestion of blood sinusoids. The pancreatic tissue revealed shrunken and degenerated acini with pyknotic nuclei, hemorrhage, necrotic area, inflammatory cells, fatty cells, and congested blood capillaries. In the muscle tissue, fiber core dissociation, edema, necrosis, segmented fibers, and inflammatory cells were detected. The gill tissue demonstrated dilation and congestion of blood vessels, complete lamellar fusions, lifting of epithelium, shortening and degeneration of secondary lamellae, hyperplasia, and deposition of MPs between primary lamellae. In the spinal cord and notochord, the effects were degeneration and protrusion of meninges, deformation and deviation of notochord from its central axis, edema, degeneration of notochord (disappearance of vacuolar cells), deviation of spinal cord from the central axis, and loss of vacuolar cells in notochord. The intestinal tissue exhibited degeneration of basement membrane, inflammatory cells, goblet cells, atrophy of submucosa, pyknotic nuclei, hemorrhage, and vacuolization of mucosal cells. The histopathological changes in different organs were noticed even post-exposure in fish exposed to MPs compared to those in control fish and these changes were concentration dependent. In conclusion, these data together with our previous data suggest that MPs can cause different changes, ranging from biochemical alterations in single cells to lesions in the entire tissue, which can affect the vitality and life of fish.