Fish are essential as income and food in many developing countries. In the international policy arena, there is increasing emphasis on promoting ‘nutrition-sensitive’ fisheries – which focus on enhancing social, food security and human nutrition benefits. But what does this actually mean for practical fisheries management? And how do the ecological complexities that underpin fisheries resources constrain or enable this type of approach? In Timor-Leste, a country with widespread poverty and undernutrition, small-pelagic fisheries are small-scale, under-developed and un(der‑) regulated, and hence there is potential to enhance these fisheries’ contributions to people’s diets and livelihoods. Using Timor-Leste’s sardine fisheries as a case-study, this paper explores the social and biophysical challenges and opportunities for developing a sustainable fishery with a ‘nutrition-sensitive’ approach. These fisheries are seasonal and comprised of mixed species; catches fluctuate from year-to-year and there is limited data on stock size or connectivity. Through this study, it is concluded that a nutrition-sensitive approach requires a whole-of-(food)-system perspective. While increasing fish supply through higher catches may lower prices and increase economic access to fish, other food system components should also be addressed, such as reducing post-harvest waste, promoting processing opportunities and food safety, and public awareness to encourage fish consumption.