A step further from waste to feed: Integrating duckweed (Lemna spp.) into circular aquaculture via black soldier fly (Hermetia illucens) production

• Application of black soldier fly larvae (BSFL), reared on duckweed, as fish feed • BSFL reared on duckweed shows early growth advantage but lower final weight • African catfish feed were partially replaced by BSFL meal, reared on duckweed • No relevant differences found in key indicators compeared to control fish feeding The aim of our study was to investigate the integration of duckweed ( Lemna spp .) as an aquaculture by-product into circular farming systems. In this research, black soldier fly ( Hermetia illucens , BSF) larvae were reared on duckweed, and the resulting larval meal was subsequently utilized in the feeding of African catfish ( Clarias gariepinus ). During BSF larval rearing, duckweed-containing substrate (DW) and, as a control, chicken layer feed (CLF) was used. The results indicated that larvae feed on the DW exhibited faster initial growth during the first three days; however, over five days, the CLF group achieved significantly higher final weight (DW: 85.6 ± 6.3 mg; CLF: 97.8 ± 4.9 mg). No significant differences were observed between the DW and CLF groups in terms of crude protein, fat, ash, chitin content, or survival rate (P > 0.05). However significant differences were found for several fatty acids (C10:0, C12:0, C14:0, C14:1, C16:1, C17:0, C18:2, C18:3, C20:4). A commercial fish feed was used as the African catfish control, while the experimental groups had 33% of the complete feed replaced with larval meal produced from the different substrates (DW33; CLF33). During catfish fry rearing, no significant differences were observed in measured key performance indicators (survival rate, biomass, average body weight, average body length, feed conversion rate, and specific growth rate). According to our results the integration of duckweed into circular aquaculture systems represents a promising approach with substantial potential for sustainable feed production via the valorization of a natural and underexploited vegetal resource.