46 JUNE 2025 • WORLD AQUACULTURE • WWW.WAS.ORG moderate inclusion rates (4 - 5%) of BSFL to provide its beneficial bioactive compounds, such as antimicrobial peptides (AMPs), encoding around 50 different AMP-related genes and medium-chain fatty acids like lauric acid. It is suggested that the presence of such AMPs and lauric acid may enhance disease resistance or stimulate an immunomodulatory effect, although this has been scarcely studied in fish. However, recently, we found enhancing rainbow trout performance and gut health while mitigating the negative effects of high SBM diets (Fawole et al. 2021; Hossain et al. 2021; Kumar et al. 2021; Singha et al. 2025). Besides providing a background on the concept of functional feed ingredients in general, this article synthesizes our recent research findings exploring the integration of BSFL as a functional ingredient, highlighting its positive impacts on trout growth, nutrient utilization, gut health, and immune function, thereby supporting sustainable and economically viable aquafeed solutions. Feed Additives, Functional Additives, Ingredients, and Functional Ingredients: Clarifying the Confusion A ‘feed additive’ is a substance deliberately added to animal or aquaculture feed in relatively small quantities to achieve specific outcomes, including improving feed quality, nutritional value, digestibility, shelf-life, palatability, or animal productivity. Feed additives may also Feed formulations for farmed fish have traditionally relied on fishmeal to provide the bulk of dietary protein. Many alternative feed ingredients such as soybean meal (SBM), soy protein concentrate, canola meal, canola protein concentrate, corn gluten meal, cottonseed meal, peas, and wheat gluten meal have been investigated and used in aquaculture feeds to replace fishmeal and reduce the cost of fish production. Currently, SBM is a core ingredient in feed formulation rather than an alternative ingredient because of its availability, favorable amino acid profile, and relative cost-effectiveness. Despite these advantages, high inclusion levels of SBM pose significant challenges, particularly for carnivorous species like rainbow trout (Oncorhynchus mykiss), due to the presence of anti-nutritional factors (ANFs) including phytic acid, oligosaccharides, saponin, trypsin inhibitor, and lectins. These ANFs can induce intestinal inflammation, disrupt gut epithelial integrity, and compromise nutrient absorption, ultimately affecting overall fish health and performance. The black soldier fly larvae (BSFL, Hermetia illucens) meal has emerged as an alternative source of protein in many industries, with aquaculture being a prominent interest. However, practical challenges, including economic feasibility and adverse effects at higher inclusion levels, suggest that BSFL is optimally positioned not as a complete replacement for traditional protein sources but rather as a complementary functional feed ingredient. This strategic repositioning utilizes FIGURE 1. The concept of feed additives, functional Additives, ingredients, and functional ingredients. FIGURE 2. Lauric acid content in the whole and defatted BSFL (Source: EnviroFlight LLC). Feed formulations for farmed fish have traditionally relied on fishmeal to provide the bulk of dietary protein. Many alternative feed ingredients such as soybean meal (SBM), soy protein concentrate, canola meal, canola protein concentrate, corn gluten meal, cottonseed meal, peas, and wheat gluten meal have been investigated and used in aquaculture feeds to replace fishmeal and reduce the cost of fish production. Repositioning Black Soldier Fly Larvae (BSFL) in Trout Diets Krishna Pada Singha and Vikas Kumar
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