The sustainability of aquaculture has been a key topic since the beginning of the millennium. Over the years, efforts have been made , especially for carnivorous species, to achieve nutritional efficiency in the sector by lowering the fish-in-fish-out ratio of feeds. And by finding sustainable and cost-effective terrestrial ingredients that can meet the necessities of carnivorous species, while still maintaining the quality of the final product1 . In recent years, many plant-based ingredients have been proven as viable alternative ingredients for aquaculture feeds , with soybean meal (SBM) becoming one of the most used alternatives for the partial replacement of fishmeal (FM) in commercial aquafeeds . However, SBM use comes with challenges. Significant inclusions of SBM in fish diets may negatively impact fish health due to intrinsic anti-nutritional factors, which might induce inflammatory responses in fish’s distal intestine2. This issue can be mitigated by using sophisticated processing techniques, that come at considerable cost3,4. Additionally, replacing FM with SBM may not produce feeds that provide reliable all-round nutrition for carnivorous fish species, as earlier studies had indicated. Furthermore, practices associated with soy production, such as deforestation and pesticide use are environmentally problematic. One promising alternative to SBM are insect meals (IM). As a component of their natural diet, i nsects provide a sound balance of amino acids, lipids, vitamins and minerals for salmonids5 , such as rainbow trout (Oncorhynchus mykiss) . Moreover, insect production can utilise food waste : forming part of the circular economy. Plus, the utilisation of normally wasted products makes insect production economically competitive.
This study evaluated the effect of substituting up to 100% of SBM protein with Black soldier fly (Hermetia illucens) meal (BSFM) with and without addition of 0.3% guar gum, with respect to growth performance, feed utilization and health of rainbow trout.
Materials and Methods
A dose-response study was conducted with a homogeneous group of juvenile rainbow trout (initial body weight: 135.8 ± 15.3g), randomly distributed in twenty 0.33m3 circular tanks. Ten balanced experimental diets were formulated to be isonitrogenous (45 %) and isolipidic (28 %) by replacing SBM with increasing levels [0% (control), 25%, 50%, 75%, and 100%] of BSFM, with and without addition of guar gum (0.3%) . The fish were fed ad libitum by hand for a period of 69 days (6 days a week) and growth performance, feed utilization efficiency, and nutrient digestibility were evaluated.
At the end of the experiment, all groups showed a linear positive correlation between the increasing replacement of SBM with BSFM with all measur ed fish performance parameters [final body weight (FBW), specific growth rate (SGR), total feed intake (TFI) and feed conversion ratio (FCR)]. The addiction of 0.3% guar gum had no effects on fish performance.
The results suggest that the inclusion of high amounts of BSFM in rainbow trout diets can be a viable option to replace plant-based ingredients in aquafeeds, with respect to important performance parameters . However, although there is growing evidence of the benefits of insect components in aquafeeds , further research is needed to fully understand the potential advantages and limitations of including insect protein in aquafeeds .
This work was funded by the European Union´s Horizon 2020 research and innovation programme under the Marie Skłodowska -Curie grant agreement No. 956481.
1. Naylor, R. L., Hardy, R. W., Buschmann , A. H., Bush, S. R., Cao, L., Klinger, D. H., Little, D. G., Lubchenco , J., Mann, R., & Troell , M. (2021). A 20-year retrospective review of global aquaculture. Nature, 591(7851), 551–563. https://doi.org/10.1038/s41586-021-03308-6
2. Merrifield, D. L., Olsen, R. E., Myklebust , R., & Ringø , E. (2011). Dietary Effect of Soybean (Glycine max) Products on Gut Histology and Microbiota of Fish. In InTech eBooks. InTech . https://doi.org/10.5772/20101
3. Schumann, M., Holm, J., & Brinker, A. (2022). Effects of Feeding an All-Plant Diet on Rainbow Trout Performance and Solid Waste Characteristics. Aquaculture Nutrition, 2022, 1–11. https://doi.org/10.1155/2022/1694245
4. Kumar, V., Hossain, M. S., Ragaza , J. A., & Benito, M. (2020). The Potential Impacts of Soy Protein on Fish Gut Health. In IntechOpen eBooks. IntechOpen . https://doi.org/10.5772/intechopen.92695
5. Nogales-Mérida, S., Gobbi, P., Józefiak, D., Mazurkiewicz, J., Dudek, K., Rawski, M., Kierończyk, B., & Józefiak, A. (2019). Insect meals in fish nutrition. Reviews in Aquaculture , 11(4), 1080–1103. https://doi.org/10.1111/raq.12281