Aquaculture production in Croatia has experienced rapid growth, nearly doubling since 2017. White fish and tuna farming have seen significant increases, while mussel and oyster cultivation has declined. The production capacity of shellfish falls far short of the target of 5,000 tons set by the Aquaculture Development Strategy (2014-2020). Significant production increases cannot be achieved without incorporating new farming areas and leveraging the potential of integrated shellfish and fish farming. This research was conducted at a commercial shellfish farm in the Novigrad Sea and under the conditions of integrated aquaculture on a fish farm near the island of Vrgada. Biometric characteristics of mussels were monitored on a monthly basis. The aim of the study was to determine whether mussels produced under integrated farming conditions have the same potential for commercial production as those produced in traditional farming areas. The purpose of the study is to use the obtained data for better planning of increasing shellfish farming in the Adriatic. According to the results, the growth of mussels under integrated aquaculture conditions near the island of Vrgada was faster compared to mussels cultivated in the Novigrad Sea. Conversely, a comparison of the condition index indicates that mussels from the Novigrad Sea were better filled with meat over a longer period compared to mussels from integrated aquaculture on Vrgada. The statistically significantly higher value of δ 15Nair in mussel tissue was observed at the location with traditional cultivation in the Novigrad Sea compared to the integrated cultivation of fish and mussels near the island of Vrgada (P<0.001). The Novigrad Sea emerges as an area with higher productivity compared to the location near Vrgada, despite the influx of nutrients from the fish farming site, as evidenced by higher nitrogen stable isotope ratios and reflected in an increased condition index for a significant part of the year