This thesis presents the research results of the impact of marine contamination, with emphasis on microplastics, on the biological responses of red mullet (Mullus barbatus Linnaeus, 1758), hake (Merluccius merluccius Linnaeus, 1758) and common pandora (Pagellus erythrinus Linnaeus, 1758) in the area of the Neretva canal in the southern Adriatic Sea. In order to determine the possible impact of contamination related to ports, tourist and agricultural activities, marine current movements, as well as the Neretva River input, levels of biomarkers in fish muscles were determined as biological indicators of neurotoxicity (acetylcholinesterase, AChE), oxidative (malondialdehyde, MDA and total glutathione, GSH) and general stress (total cytosolic proteins, TP). The presence of microplastics was determined in the digestive tract of the fish by acid digestion using nitric acid and hydrogen peroxide, followed by filtration. Plastics presented 17% of the total trawl catch, and examination on a stereo microscope confirmed the existence of microplastic fragments in the gut content of each analysed fish, indicating food uptake. There were not significant differences in biomarker levels between locations, so significant impact of contamination was not confirmed, but mostly indication of species specific differences. Thus, for the first time, basal levels of biomarkers were defined. Concentrations/activities in the muscles of red mullet, hake and common pandora from the Adriatic Sea ranged for MDA 3-5 nmol g-1, GSH 140-150 nmol g-1, AChE 30-70 nmol min-1 mg-1 and TP 7-12 mg ml-1. Regarding the presence of microplastic fragments in studied samples, it is certainly necessary to further investigate the impact of this form of pollution on the Adriatic Sea.