Introduction
Biofloc can be used as a source of live feed for farmed organisms . Furthermore , its excess and by-products have been also used successfully as a feeding source for insects, such as Hermetia illucens (Zhang et al., 2023) . What is more, feeding larvae with biofloc waste may be a sustainable strategy which does not only help to recycle aquaculture’s waste but that also converts it into a valuable alternative protein source (APS). Such approach would help lead aquaculture towards more sustainable practices that also align with the circular economy principles. C onsequently, there is a current need to assess biofloc by-products as a potential feed for larvae to confirm if those insects can be turned into a nutritious protein-rich flour for aquafeed production.
Materials and methods
Tenebrio molitor larvae were farm ed in plastic containers for two weeks in a room with controlled environmental parameters. All experimental groups were fed wheat bran as dry feed. The control group received carrots twice a week as a source of hydration, while the other experimental groups were given biofloc 1, 2, or 3 times per week as substitute for the carrot. Larvae weight, non-eaten food weight and feces weight were measured weekly. At the end of the experimental trial , zootechnical parameters such as weight gain , mortality rate, feed conversion ratio (FCR) and frass production ratio (FPR) were calculated. Larvae were frozen and stored for their posterior nutritional composition analysis.
Results and discussion
As shown in Table 1, control group s reached higher final biomass levels and provided lower FCR and FPR values during the first and second week of the experimental trial, reaching bigger larvae sizes too (Figure 1) . In contrast, biofloc and wheat bran fed groups showed higher FCR and FPR values, indicating a lower feed conversion efficiency and confirming that some of the administered biofloc was not turned into biomass. However, biofloc was consumed at a higher rate when administered more frequently and no mortality rate could be observed in any of the experimental groups (Fig ure 2).
Although no literature has been found regarding biofloc’s potential as a moisture source for insect feeding, one study evidenced that biofloc by-products mixed with wheat bran provided optimal growth results when tested as an alternative dry diet for blacksoldier fly larvae (Zhang et al., 2023) . Despite the fact that fly larvae performed better than T.molitor when fed with the above-mentioned mix , our carrot-fed group provided similar results to other works in which mealworms were fed different moist raw materials (such as tangerine shells or mushroom spent substrate) (Kim et al., 2017) . Therefore, even though biofloc may be a nutrient-rich substrate with probiotic effects, mealworm larvae seem to prefer, digest and assimilate better other moist ingredients like carrots. Nevertheless , biofloc may still be a promising dry ingredient when mixed with vegetal by-products.
Conclusion
Although biolfoc by-products can be used as a suitable and safe ingredient for T.molitor larvae feeding, carrots were a more effective moisture source. Nevertheless, biofloc may still be a potential nutrient-rich ingredient for larvae feeding when mixed with other dry raw materials.
Acknowledgments
This work was supported by I+D+i Research Project: “Pursuing the zero waste in Biofloc Technology to produce a sustainable and biosafe aquaculture product (ZeroFloc )” (PID2023-149570OB-I00). J. Gómez-Aguilera contract was supported by European Union Next Generation-Plan of Conselleria d’innovació , Universitats , Ciència i Societat Digital of Generalitat Valenciana (INVEST/2022/434).
References
Kim, S. Y., Kim, H. G., Yoon, H. J., Lee, K. Y., & Kim, N. J. (2017). Nutritional analysis of alternative feed ingredients and their effects on the larval growth of Tenebrio molitor (Coleoptera: Tenebrionidae). Entomological Research , 47(3), 194–202. https://doi.org/10.1111/1748-5967.12236
Zhang, H., Sun, T., Tan, H., Lv, X., Liu, W., & Luo, G. (2023). Using black soldier fly larvae (Hermetiaillucens ) converted the bioflocs produced with shrimp solid waste. Aquaculture , 568, 739329. https://doi.org/10.1016/J.AQUACULTURE.2023.73932