As sardine oil became a crucial raw material for the Japanese empire’s industrial expansion in the hydrogenated oil industry in the early twentieth century, colonial Korea’s sardine oil industry emerged as a key site of scientific engagement for capital accumulation. Shaped by their fishing experiences and aquatic knowledge, Korean laborers not only developed local practices for sardine oil production but also adapted and adjusted them to enhance oil output and quality. Focusing on colonial subjects’ technological prowess, this project examines the formation of vernacular science in colonial fisheries. It argues for the agency of Korean fishery laborers as technologists and knowledge producers. By centering the role of the colonized in shaping fishery science, the project offers a new framework for understanding science and technology in the context of colonialism.