Waste generated during aquaculture can be converted into bioflocs . Black soldier fly larvae (BSFL) are a valuable resource for the treatment of organic waste. This study evaluated the effect of feeding BSFL with bioflocs for the first time with the aim of providing a new approach for the resource utilization of aquaculture solid waste. Six treatment groups were established by feeding BSFL with fermented bioflocs (A1), bioflocs (B1), fermented wheat bran (A2), wheat bran (B2), fermented mixed diet (A3), and mixed diet (B3). The survival rates (SR) of the six treatment groups were not significantly different. The crude protein and lipid contents of the final BSFL were 50.9–63.94% and 3.96–7.73%, respectively, in the six treatment groups. The BSFL of B2 had the highest crude protein and lowest crude ash content while those of B1 had the lowest crude protein content and highest crude ash content. Oleic and linoleic acids were the predominant fatty acids in BSFL for all groups (more than 53.25%) and B3 BSFL contained three essential fatty acids (EFAs). By analyzing the effect of BSFL culture and biofloc reduction, we determined that bioflocs and wheat bran mixed at a ratio of 6:4 (dry matter) is ideal for cultivating BSFL. Overall we found that BSFL can directly treat bioflocs and the bioflocs intend provide ideal nutrients for BSFL, which implies a potential method for cleaner production in aquaculture.
The bioflocs were obtained from a commercial-scale Litopenaeus vannamei farming system (Chuzhou, China). Hermetia illucens eggs hatched with wheat bran (70% moisture) for 4–5 days. Newly hatched larvae were reared on wheat bran for 3 days before they were used in the ex periments. For fermented wheat bran, dry wheat bran was dissolved in water to 30% dry matter. Six types of food substrate were designed for the experiments. Four materials (bioflocs , fermented bioflocs , wheat bran, and fermented wheat bran) described above as well as two mixed substrates: the combined substrate and fermented-combined food substrate. The combined substrate was created by mixing bioflocs and dry wheat bran at a dry matter ratio of 6:4. The fermented-combined substrate was created by mixing bioflocs and dry wheat bran at dry matter ratio of 6:4 before sterilization at 121 ℃ for 15 min. The experiments were conducted in transparent plastic cans with perforated lids, controlled moisture at 70%, and at 28 ℃. In each can, 400 larvae (0.2–0.5 cm in size, 5 d old) were placed and the feeding larval density was 5.10 tails/cm2 . Feeding frequency was kept consistent for all groups. It began to harvest the BSFL when the first larval was found to pupate in all groups. The experiment lasted for 16 days.