Duckweed as a Sustainable Aquafeed: Effects on Growth, Muscle Composition, Antioxidant and Immune Markers in Grass Carp

Duckweed (<i>Spirodela polyrhiza</i>), a fast-growing aquatic plant rich in protein and bioactive compounds, offers a sustainable alternative to conventional aquafeed protein sources. This study evaluated the effects of incorporating 25-75% duckweed meal into a commercial feed on grass carp (<i>Ctenopharyngodon idella</i>) over a 6-week trial. Fish meal, wheat starch, and vegetable oil was added in amounts to obtain isonitrogenous and isoenergetic diets. Additionally, another grass carps were used for extended feeding until they reached approximately 1000 g, using the feed with the optimal duckweed inclusion rate (25%). Fish fed a diet consisting of 75% commercial feed and 25% duckweed meal (F75D25) exhibited significantly higher weight gain. Muscle analysis revealed increased protein content (up 15%, <i>p</i> < 0.05) and improved amino acid and fatty acid profiles. Liver, muscle, and blood assays showed elevated antioxidant enzyme activities (SOD up 20%, LYS up 18%; <i>p</i> < 0.05) and immune markers (CRP, GOT; <i>p</i> < 0.05), indicating enhanced health status. Transcriptomic and metagenomic analyses confirmed the upregulation of immune-related genes (e.g., SOD1, IL-6; fold change > 2, <i>p</i> < 0.01) and beneficial shifts in gut microbiota (e.g., increased Firmicutes). These findings highlight duckweed's potential as a nutrient-rich, health-promoting ingredient for sustainable aquaculture diets.