The determination of 63Ni was carried out on fish samples of cod (Gadus morhua), herring (Clupea harengus), sprat (Sprattus Sprattus) and samples of sediment core from the Gdańsk Bay. In contrast to stable nickel, 63Ni is non-uniformly distributed within the fish. More than 95% of total 63Ni content in cod and herring is located in fillet with skin and scale. Our data suggesting, that mechanism for uptake of 63Ni in cod and herring is by passive adsorption onto the surface of skin and scale mucus. The concentration of 63Ni in analysed sediment lies within the range from 0.5 to 3.8 mBq.g-1 dry wt, while values of its specific activity ranged between 10 and 70 Bq.g-1.