Reconciling Cost and Environmental Sustainability in Finfish and Crustacean Aquafeeds: A Critical Narrative Review of Ingredient, Formulation and Feeding Strategies

Abstract

Feed is the dominant economic cost and the principal environmental hotspot of fed aquaculture, yet the two objectives of lowering feed cost and lowering environmental burden are frequently assumed to coincide rather than demonstrated to do so. This critical narrative review examines strategies intended to make feeds for farmed finfish and crustaceans simultaneously cost-effective and environmentally sustainable, and evaluates whether the available evidence supports that dual claim. Literature was identified through structured searches of multidisciplinary and life-science scholarly indexes, institutional sources and citation chasing, with emphasis on peer-reviewed evidence published from 2000 onwards and selective use of foundational earlier work. The synthesis is organised around five themes: the metrics used to judge cost and sustainability; replacement of marine ingredients with terrestrial plant proteins and oils; novel ingredients, including insect meals, microbial biomass and algae; circular use of processing by-products and residual streams; and efficiency gains achieved through feed management, precision feeding, genetic selection and in-situ nutrient recycling. The evidence is strongest that improved feed conversion and by-product valorisation reduce both cost and environmental pressure. Evidence for plant-based substitution is robust for growth at moderate inclusion levels but indicates burden shifting towards land, freshwater and phosphorus use and a dilution of omega-3 long-chain polyunsaturated fatty acids in farmed products. Novel ingredients frequently perform well in controlled trials, but their environmental advantage depends strongly on substrate, energy source and allocation choices, and their economic competitiveness is demonstrated in only a small number of context-specific analyses. Crustacean feeds, smallholder systems in Asia and Africa, and long-term performance under commercial conditions remain under-represented. Conventional indicators such as feed conversion ratio and fish-in to fish-out ratios capture only part of the relevant trade-offs, and conclusions often reverse when nutrient retention, economic allocation or consequential life cycle perspectives are applied. The review concludes that no single ingredient class offers a general solution; the most defensible pathway combines nutrient-based least-cost formulation, efficiency-oriented feeding and breeding, and preferential use of residual streams, evaluated with harmonised economic and environmental metrics at commercial scale.