Microplastics (MPs), as emerging pollutants in aquatic environments, pose a serious threat to aquatic health and human food safety due to their biopersistence and ability to accumulate in the food chain. The aim of this study was to investigate the amount and pattern of microplastic accumulation in the gills, gastrointestinal tract (stomach and intestines), and liver under different exposure treatments, including feeding with contaminated feed, exposure to water containing microplastics, and combined exposure to microplastics and nickel metal.The study hypothesized that the route of exposure, type of polymer, and presence of co-pollutants play an important role in the tissue distribution and accumulation intensity. In this experimental study, 300 Asian sea bass fry with an average weight of 38.5 ± 0.3 g were obtained from a nursery and after 14 days of acclimation, they were divided into 12 experimental groups. Treatments included dietary exposure to 1, 3, and 5 mg of microplastic per gram of feed, aquatic exposure to 50, 100, and 150 mg per 100 liters of water, combined exposure to microplastics and nickel, and a control group.The exposure period was four weeks and weekly tissue sampling was performed. After chemical digestion and filtration, the samples were counted by stereo microscopy and confirmed by FTIR. The results showed that the accumulation of microplastics in tissues was heterogeneous and dependent on the route of exposure. The gastrointestinal tract, especially the intestine, was the main reservoir with 51.4% of the total particles and its accumulation increased from 10 particles in the first week to 21 particles in the fourth week, indicating the cumulative and non-degradable nature of the pollutants. The stomach and gills acted as the primary reservoir and respiratory uptake route of the particles, respectively.Accumulation in the liver was limited and transient, indicating limited transport from the gastrointestinal tract to the circulation. Dietary