Harnessing Agricultural Weeds as Sustainable Feed Alternatives for Herbivorous Aquatic Species

The increasing demand for sustainable aquaculture practices necessitates the development of alternative feed ingredients that are nutritionally adequate, cost-effective, and environmentally sustainable. Agricultural weeds—abundant, fast-growing, and often underutilized—have emerged as promising candidates for non-fin fish herbivorous aquaculture. This systematic review investigates ten species of aquatic and semi-aquatic agricultural weeds: Alternanthera philoxeroides, Eichhornia crassipes, Lemna minor, Azolla pinnata, Amaranthus spinosus, Najas graminea, Ipomoea aquatica, Hydrilla verticillata, Salvinia molesta, and Marsilea crenata. The review evaluates their nutritional compositions, bioactive compounds, anti-nutritional factors, and effects on growth performance, feed efficiency, immunity, and survival rates in non-fin fish species. Results indicate that several weeds, notably Azolla pinnata and Amaranthus spinosus, contain high crude protein levels—up to 30 and 28% respectively—alongside essential amino acids, and beneficial vitamins and minerals, making them suitable candidates for partial or full replacement of conventional feed ingredients. While certain species contain anti-nutritional factors such as tannins and oxalates, these can be mitigated through effective pre-processing techniques. Among these, fermentation has proven particularly effective, reducing tannin levels by up to 40%, while also enhancing nutrient bioavailability. The weeds reviewed also demonstrated positive effects on feed conversion ratios (FCR), immune responses, and antioxidant activity, with minimal environmental impact. This review underscores the untapped potential of agricultural weeds in promoting circular economy principles in aquaculture and highlights the need for further species-specific research, digestibility trials, and cost-benefit analyses to support their practical application in feed formulation.