A review of using duckweed (Lemnaceae) in fish feeds

One of the primary sustainability challenges in aquaculture is replacing fish meal with plant-based ingredients in aquafeeds. Plants are not optimal due to low protein content and antinutritional factors which can cause gut dysbiosis. Duckweed (Lemnaceae) is a family of aquatic plants with high protein content and has been used successfully for various types of animal feeds. In this systematic review and meta-analysis of 58 papers, we summarize the extent by which duckweed has been used in fish production including the species of fish tested, the grow-out stage of fish, and method of application. Duckweed studies spanned a total of 18 species of fish (16 freshwater and two marine) that collectively are valued at 263 billion USD annually, and comprise 28% of total aquaculture production by mass. The average experiment length was 72 days (SD 42), primarily at the fingerling life stage. Duckweed was fed to the fish through live grazing, dried, and pelleted forms with 20% inclusion as the most common formulation. The Lemna spp., dominated by L. minor, L. gibba, and unknown Lemna species, were the most commonly used for feeds. Spirodela polyrhiza was the second most common. Duckweed inclusion levels between 15% and 30% were associated with positive outcomes on fish growth and feed conversion ratio without any negative impact on survival rates. Most duckweed species, especially from Wollfiella have not been tested as a fish feed but should be explored whereas most studies focused on freshwater fishes rather than marine.