["Business Strategy and the Environment, EarlyView. ", "\nABSTRACT\nResearch on sustainable fish supply chain transformation remains fragmented across governance, financial, technological and behavioural domains, offering limited explanation for why similar initiatives produce uneven outcomes across contexts. This systematic review synthesises 213 peer‐reviewed studies from Scopus and Web of Science (1999–2025) using qualitative thematic content analysis. The synthesis develops the Layered Conditional Transformation Model (LCTM), a middle‐range theory organised across institutional, relational and operational layers and transferable to other fragmented value chains. LCTM proposes a structural feasibility mechanism in which sustainability outcomes depend more consistently on enabling institutional and relational conditions than on intervention design alone, reframing transformation as a readiness‐conditioned process. Three contributions follow: a conditional effectiveness logic explaining the divergence of outcomes, a structural coordination failure mechanism identifying how sustainability signals are transmitted or suppressed and a feasibility threshold defined as a minimum‐sufficiency diagnostic boundary that guides intervention sequencing. An integrative vignette illustrates LCTM as a pre‐investment diagnostic for identifying bottlenecks and sequencing transformation strategies.\n"]