Feed efficiency (FE) is one of the most economically and environmentally important target traits for genetic improvement since feed accounts for 50–70% of total production expenses in aquaculture worldwide. In addition to lowering production costs, reducing feed consumption per unit of biomass output also reduces emissions of nitrogen and phosphorus, which is in line with global sustainability goals for food production. The genetic framework of FE traits, molecular dissection of the targeted loci, conventional selective breeding frameworks, genomic selection, emerging biotechnological applications, major implementation challenges, and prospects are all covered in this review, which summarizes current developments in genetic improvement of FE in aquaculture. We incorporate empirical data from important farmed finfish and crustacean species, emphasizing that FE-related traits show measurable genetic variation available for selection, although reported heritability estimates vary substantially among traits, populations, phenotyping methods, and production conditions. Compared to conventional breeding techniques, the integration of high-throughput phenotyping, genomic prediction and multi-omics approaches has expanded opportunities to characterize FE variation and improve selection accuracy. However, most reported candidate loci and genes remain supported by associative rather than causal evidence, and functional validation in aquaculture remains limited. Integrated breeding approaches therefore offer feasible pathways to mitigate major constraints to genetic improvement of FE, although their practical application differs substantially among species and production systems.