Feed constitutes a significant portion of the environmental impact embedded in farmed fish production, making it a pivotal factor in enhancing aquaculture sustainability. Greater dependence on agricultural ingredients in place of fishmeal and oil has been necessary to sustain aquaculture growth, however, the implications of this shift for biodiversity impacts remain unknown. We apply a spatially explicit model to compare the biodiversity impacts of a fish-dominant and plant-dominant feed for farmed Atlantic salmon. We assess habitat impacts on 55,236 marine and terrestrial species, finding 75-77% impacted, yet the magnitude of impact is very small. On average, agricultural ingredients present greater biodiversity impacts than fishmeal and oil, underscoring the importance of responsible sourcing practices for both marine and terrestrial ingredients. Additionally, applying effective biodiversity impact assessments will be critical for the development of sustainable new feed ingredients, such as omega-3 enriched crops or single-celled proteins, going forward. We emphasise the significance of contextualising these findings through comparisons with other farmed seafood and livestock products to understand strategies for minimising biodiversity impacts across our food system.