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Food system is a powerful concept for understanding and responding to nutrition and sustainability challenges. Food systems integrate social, economic, environmental and health aspects of food production through to consumption. Aquatic foods are an essential part of food systems providing an accessible source of nutrition for millions of people. Yet, it is unclear to what degree research across diverse disciplines concerning aquatic foods has engaged food systems, and the value this concept has added. We conducted a systematic review of fisheries, aquaculture and aquatic food literature (2017-2019) to determine the following: the characteristics of this research; the food systems components and interrelations with which research engaged; and the insights generated on nutrition, justice, sustainability and climate change. Sixty five of the 88 reviewed articles focussed on production and supply chains, with 23 considering human nutrition. Only 13% of studies examined low-and middle-income countries that are most vulnerable to undernutrition. One third of articles looked beyond finfish to other aquatic foods, which illuminated values of local knowledge systems and diverse foods for nutrition. When aggregated, reviewed articles examined the full range of food system drivers-biophysical and environmental (34%), demographic (24%) and socio-cultural (27%)-but rarely examined interactions between drivers. Future research that examines a diversity of species in diets, system-wide flows of nutrients, trade-offs amongst objectives, and the nutritional needs of vulnerable social groups would be nudging closer to the ambitions of the food systems concept, which is necessary to address the global challenges of equity, nutrition and sustainability. | 35 SIMMANCE Et Al. 42 4.2.1 Relationships between food systems components researched 44 4.3. Emerging challenges for food systems 45 4.4. Nudging towards the concept of food systems 46 4.4.1 Consider a broader set of aquatic food types amidst diverse diets 47 4.4.2 Examine system-wide flows of nutrients and tradeoffs amongst objectives 47 4.4.3 Focus on vulnerable and marginalized social groups 47 5. CONCLUSION 48

Wild-caught fish provide an irreplaceable source of essential nutrients in food-insecure places. Fishers catch thousands of species, yet the diversity of aquatic foods is often categorised homogeneously as 'fish', obscuring understanding of which species supply affordable, nutritious, and abundant food. Here, we use catch, economic and nutrient data on 2,348 species to identify the most affordable and nutritious fish in 39 low and middleincome countries. We find that a 100 g portion of fish cost between 10-30% of the cheapest daily diet, with small pelagic fishes (herrings, sardines, anchovies) the cheapest nutritious fish in 72% of countries. In sub-Saharan Africa, where nutrient deficiencies are rising, <20% of small pelagic catch would meet recommended dietary fish intakes for all children (six months-four years old) living near to water bodies. Nutrition-sensitive policies that ensure local supplies and promote consumption of wild-caught fish could help address nutrient deficiencies in vulnerable populations. Main TextA nutrient-adequate diet is unaffordable for almost three billion people, particularly in Southern Asia and sub-Saharan Africa, contributing to growing global malnutrition and food insecurity 1,2 . In these regions, fish is a key component of the food system that is often produced by small-scale sectors 3 . Critically, in these settings fish provide a local source of highly bioavailable micronutrients such as iron and zinc 4 that are often lacking in diets 5 . In populations that have access to and consume relatively high amounts of fish, studies have demonstrated improved pregnancy and birth outcomes 6,7 and faster child growth 8 . Fish is expected to contribute to healthy diets where it is affordable and accessible, but the cost and availability of nutrient-rich foods, including fish, is highly variable across and within countries 9-11 . In the Global South, lower household income 9 and proximity to markets 12 and fisheries 13 can restrict access to fish, and thus limit its potential to contribute to people's health. Yet scarcity of data on fish prices at the species-level mean that large-scale analyses of fish affordability typically combine aggregate products by ecosystem category (e.g. pelagic or demersal fishes 14 ) or simply as 'fish' 10 . These data simplifications limit understanding of how the affordability of fish varies among species, production methods, and locations. Furthermore, productivity and nutrient content of wild-caught fish varies greatly 4 , such that micronutrient-rich fish may not be available (i.e. produced or traded) and affordable in every country. Three key questions remain unanswered: 1) where are wild, micronutrient-rich fish affordable?; 2) which wild-caught species are the cheapest, most micronutrient-rich fish?; and 3) where do fisheries provide an abundant supply of nutritious food? Here, we examine the affordability and supply of wild-caught fish in 39 low-and middleincome countries. We compile information on catch weight, price (at point of landing, 'exvesse...

Poverty and food insecurity persist in sub-Saharan Africa. We conducted a secondary analysis of nationally representative data from three sub-Saharan Africa countries (Malawi, Tanzania, and Uganda) to investigate how both proximity to and engagement with small-scale fisheries are associated with household poverty and food insecurity. Results from the analysis suggest that households engaged in small-scale fisheries were 9 percentage points less likely to be poor than households engaged only in agriculture. Households living in proximity to small-scale fisheries (average distance 2.7 km) were 12.6 percentage points more likely to achieve adequate food security and were 15 percentage points less likely to be income poor, compared to the most distant households. Households distant from fishing grounds (>5 km) were 1.5 times more likely to consume dried fish compared to households living close. Conserving the flow of benefits from small-scale fisheries is important for meeting the Sustainable Development Goals in the region.

Small-scale inland capture fisheries provide an important source of nutritious food, employment and income to millions of people in developing countries, particularly in rural environments where limited alternatives exist. However, the sector is one of most under-valued fisheries sectors and is increasingly experiencing environmental change. This study adopts a Sustainable Livelihoods Approach and investigates how important a fluctuating inland fishery is to livelihoods, and how local perceptions on challenges corresponds to global evidence. Through an innovative participatory method; photovoice, the lived experiences and perceptions of fishers are depicted. The findings illuminate the valuable role of the sector to food and nutrition security and the complex nexus with vulnerability to climate change. The study responds to the call for more local level assessments of the impacts of climate change on inland fisheries in data-limited environments, and the value of the sector in underpinning the Sustainable Development Goals.