Seascape connectivity is widely recognised as a key driver of fish population structure, yet there is limited synthesis of the spatial scales over which these effects operate. We review studies globally that assessed connectivity effects on adult and juvenile finfish to determine whether “rules of thumb” can be established for the spatial scale of connectivity between ecosystems for coastal management. A structured literature search identified 69 studies (1997–2025) reporting significant relationships between spatial metrics (distance or area) and fish assemblage attributes. In total, 499 spatial patterns were extracted across six ocean basins and ten ecosystem types. Most patterns (87%) showed positive effects of connectivity, with more fish at sites nearer to or connected with larger habitat patches. Connectivity with mangroves and seagrass was most influential in structuring fish assemblages. Benefits extended from tens of metres to >100 km, with spatial scales generally predictable within ecosystems. Vegetated ecosystems were typically linked over hundreds to a few thousand metres, whereas open-coast features extended over several to tens of kilometres. However, values varied across ocean basins, indicating regional uncertainty. Connectivity benefits are pervasive and generally positive, but spatial scales vary among ecosystems, supporting context-specific, evidence-based conservation and restoration planning.