Nutritional Landscape of Fish Sold in Portugal: Composition, Ratios, and Nutrient Density Across 40 Species

This study applies an integrated nutrient-density and multivariate classification framework to benchmark the nutritional quality of fish using harmonized food composition data. Energy, macronutrients, fatty acids, vitamins, and minerals were quantified and combined into lipid and mineral ratios (PUFA/SFA, Na/K, Ca/P, Fe/Zn) and a modified Nutrient Rich Foods Index, followed by principal component analysis and k-means clustering. The framework was applied to 40 raw fish species commonly available on the Portuguese market. Three coherent nutritional groups were identified: lean white fish (low fat, high protein density), oily pelagics (high lipid and vitamin content), and lipid-rich outliers (eel, lamprey). Oily fish provided the highest EPA+DHA concentrations, with median 1400 mg/100 g, all oily species exceeding the EFSA adequate intake of 250 mg per portion. Lean fish maximized protein yield per calorie, whereas oily species concentrated vitamins D and B12 and exhibited favorable PUFA/SFA (>0.4) and Na/K (<1.0) ratios. Ca/P ratios were uniformly below adequacy levels, reflecting low calcium in fillet tissue. Overall, fish species displayed complementary nutrient-density profiles, with lean species optimizing protein efficiency, while oily species delivering cardioprotective lipids and fat-soluble vitamins, and outliers represented concentrated but energy-dense nutrient sources. The proposed analytical framework provides a transferable approach for comparative nutritional profiling of fish and seafood across food composition databases. GRAPHICAL ABSTRACT Created by the authors using Canva (https://www.canva.com) and Python (v3.14) with matplotlib (v3.9.2) and seaborn (v0.13.2). • Fish distribute along dual axes of protein efficiency and lipid-associated nutrients • Oily fish provide the greatest omega-3 content, often >1.4 g EPA+DHA/100 g. • Lean fish maximize protein density, reaching ~21 g protein per 100 kcal. • Oily species concentrate vitamins D and B12 with favorable PUFA/SFA ratios. • A dual-axis framework outperforms single-metric nutrient rankings for fish comparison.