As climate change drives aquaculture into more energetic and exposed offshore environments, the sustainability of fish farming increasingly relies on resilient mooring systems. In this study, a numerical model of an offshore fish pen was developed and analysed using OrcaFlex and the Morison force model, accounting for flow effects such as blockage and wake to better predict hydrodynamic forces due to wave-current interactions. The model was validated against experimental data, though some deviations were noted, likely due to limitations in the net model mesh and the Morison model’s inability to fully capture floating collar deformations. Despite these limitations, important insights were gained. Results show a strong relationship between mooring line tension and floating collar motion, with heave increasing alongside wave height and period, highlighting the need for mooring designs that withstand high-amplitude waves. Surge motion also significantly impacted mooring tension. A catenary mooring system outperformed a taut mooring system, displaying lower tension under high wave and current conditions but larger collar motions, particularly in surge. The most significant wave-current interactions occurred when waves and currents were in opposite directions, while perpendicular interactions had minimal impact.