The rapid expansion of aquaculture industry is severely restricted by the shortage of key feed ingredients such as fishmeal and fish oil. Application of marine plants (macro and microalgae) as dietary ingredients could potentially overcome the limitation of key feed ingredients used in aquafeed. Macroalgae and microalgae contain considerable amounts of protein, omega-3 long chain polyunsaturated fatty acids-enriched lipid and different bioactive functional compounds. Feeding macroalgae and microalgae meal has been proved to improve growth, overall health, reproductive performance, and fillet quality of fish. This chapter summarizes the current knowledge of the use of macro and microalgae in aquafeed and their effects on overall fish performance.