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

## TL;DR

Duckweed can be used as a sustainable fish feed for grass carp, improving growth, muscle quality, and health while reducing reliance on traditional feed.

## Contribution

This study demonstrates that duckweed inclusion in aquafeed improves fish growth and health markers in grass carp.

## Key findings

- Fish fed 25% duckweed had higher weight gain and better food efficiency.
- Duckweed improved muscle protein content and antioxidant enzyme activity in fish.
- Gut microbiota shifted toward beneficial types with duckweed inclusion.

## Abstract

Feeding fish is one of the biggest costs in aquaculture, and traditional ingredients such as soybean meal and fishmeal are becoming more expensive and place pressure on the environment. Duckweed, a small floating water plant, grows very fast and is rich in protein and healthy compounds. This study tested whether duckweed could constitute part of the normal diet of grass carp, one of the most important farmed fish in Asia. We compared diets where commercial feed was partly or fully incorporated with duckweed. The best results were found when 25% of the feed was incorporated. Fish in this group grew faster, used their food more efficiently, and developed better muscle quality than fish fed only commercial feed. We also observed improvements in fish health, including stronger antioxidant defenses and better immune responses. The gut bacteria of these fish also shifted toward more beneficial types. These results show that duckweed is a promising and environmentally friendly feed ingredient. Using duckweed could lower costs for farmers, reduce reliance on conventional feed ingredients, and improve the sustainability of aquaculture.

Duckweed (Spirodela polyrhiza), 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 (Ctenopharyngodon idella) 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%, p < 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%; p < 0.05) and immune markers (CRP, GOT; p < 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, p < 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.