Using black soldier flies as a component of aquafeed is a common approach, and so is using black soldier fly frass as a soil amendment. As it turns out, this frass can also be used to fertilize water in multilevel recirculating aquaculture.

Abdessan, R., Zhumanova, M., Luo, X.L., Yan, J.J. and Ji, H., 2024. Influence of direct supplementation of different levels of black soldier fly larvae (Hermetia illucens) frass to a recirculating aquaponic system: focusing on fish (Cyprinus carpio var. specularis), plant (Lactuca sativa var. ramosa Hort) and water quality. Aquaculture, 741608. https://doi.org/10.1016/j.aquaculture.2024.741608

The production of insects tends to increase due to their capacity to convert organic waste into protein. Nonetheless, insects cannot process all organic waste entirely. Consequently, a substantial quantity of frass - a by-product composed mainly of larval excrement along with chitin remains post-production, serving as an excellent organic supplement to promote plant growth. Therefore, this study firstly conducted to find the optimal level of black soldier fly larvae frass (BSFLF) for media-based aquaponic systems. Various levels (control - 0 mg/L, 2.8 mg/L, 5.6 mg/L, 11.2 mg/L) of BSFLF were directly supplemented to the aquaponic systems on a weekly basis. Totally 120 mirror carp with an average body weight of 21.59 g were randomly distributed into four groups, each with three replicates. Each tank held 10 fish, and the experiment lasted for 56 days. The results showed that: (1) The supplementation of BSFLF had no significant effect (P > 0.05) on the growth performance, feeding efficiency and biological indexes of mirror carp. However, the muscle crude protein level of mirror carp significantly increased (P < 0.05) with 2.8 mg/L of BSFLF supplementation compared to the control group; (2) Adding 11.2 mg/L of BSFLF into the system led to significant reductions (P < 0.05) in total n-3 PUFA and n-3 long-chain polyunsaturated fatty acids (LCPUFAs) content in mirror carp muscle; (3) The addition of 2.8 mg/L of BSFLF led to a significant increase (P < 0.05) in zinc (Zn) levels in the mirror carp muscle; (4) The weight of lettuce significantly increased (P < 0.05) with the supplementation of 5.6 mg/L and 11.2 mg/L BSFLF into the system; (5) Plant leaves iron (Fe) concentration in the 5.6 mg/L BSFLF supplemented group was significantly higher (P < 0.05) compared to the control group; (6) The addition of BSFLF had not significant impact (P > 0.05) on the water quality parameters. Overall, adding between 2.8 mg/L and 5.6 mg/L of BSFLF directly into the system each week is recommended for better mirror carp muscle protein content, fatty acid profile, zinc levels, and lettuce growth performance without compromising water quality.