This thesis presents the results of measuring morphological characteristics of the mussel Mytilus galloprovincialis at two sites. Measurements were made during 3 months (October, November and February) on Lake Prokljan and in the Middle Channel. The difference between the localities is represented by abiotic factors, mostly salinity. The aim of this thesis is to determine the influence of abiotic factors on the acceptance and growth of mussels and the influence of intensive fish farming on mussel growth. To this end, morphological characteristics (length, height, width and weight) of mussels were measured at two locations, near fish cages. The average measured length, width and weight (total weight and wet tissue weight) of mussels after 6 months was higher in mussels from Prokljan Lake, while the average height and weight of the shell was higher in mussels from the Middle Channel. A statistically significant difference was identified between Raslina and Ždrelac stations in terms of shellfish fitness index regardless of time (p<0.001). The results show faster growth of mussels in the Prokljan Lake after lowering the collector to a depth of 6-7 m, where the salinity is stable.