Black Soldier Fly Frass Helps both Fish and Plants Grow

Romano, N., Datta, S.N., Pande, G.S.J., Sinha, A.K., Yamamoto, F.Y., Beck, B.H. and Webster, C.D., 2023. Dietary inclusions of black soldier fly (Hermetia illucens) larvae frass enhanced production of channel catfish (Ictalurus punctatus) juveniles, stevia (Stevia rebaudiana, and lavender (Lavaridula angustifolia) in an aquaponic system. Aquaculture, 739742.

In aquaponic systems, adding supplemental nutrients to enhance plant production is common. Frass, which is the manure of insects, can be used to enhance fish and plant production, but no study has yet examined the potential to enhance both using a dietary approach in an aquaponic system. In this 8-week study, channel catfish (Ictalurus punctatus) juveniles were fed diets with, or without, 10% black solider fly (Hermetia illucens) larvae (BSFL) frass in an aquaponic system. Each aquaponic system had two different plant bed types; floating raft or media. Each plant bed consisted of three stevia (Stevia rebaudiana) and three lavender (Lavaridula angustifolia) plants in a 2 × 2 factorial design, with the main effects of dietary frass inclusion and media type. After 8 weeks, channel catfish grew significantly faster when fed a diet containing 10% BSFL frass compared to fish fed the control diet. Further, dietary frass upregulated the hepatic expression of IGFβ, IGF-1 and GHR as well as reduced intestinal inflammation based on histological observations. The muscle proximate composition of channel catfish was unaffected by diet, while only taurine was significantly reduced by dietary frass. Muscle calcium and phosphorus as well as C14:0 and C15:0 were significantly elevated by dietary frass. For plants, both stevia and lavender had significantly more biomass when frass was added to the system, while plants grown in media beds were larger than plants grown in a floating raft subsystem. Frass significantly increased phosphorus in both stevia and lavender at week 8. The higher water calcium, magnesium, and nitrate levels may have allowed for better plant growth as these are essential nutrients. The significant increase of catfish growth was likely due to the upregulation of genes responsible for growth, mitigating intestinal inflammation, and significantly enhancing diet intake. Thus, it may be recommended that feeding catfish with BSFL frass and culturing stevia and lavender in media beds can substantially improve overall productivity.