WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2025 47 support animal health, growth performance, and efficiency in various ways but do not necessarily provide significant nutritional value on their own. A ‘functional feed additive’ is a specific component included at low inclusion rates (typically 1-2%) in animal diets, specifically designed to improve the ‘physiological and health status of the animal beyond basic nutritional needs.’ These often include substances like probiotics, prebiotics, enzymes, organic acids, phytogenic compounds, antioxidants, immunostimulants, and other bioactive compounds. So, functional feed additives are a subset of feed additives, as illustrated in Figure 1. A ‘feed ingredient’ is any component included in animal feed to provide essential nutritional value, such as protein, carbohydrates, fats, vitamins, or minerals, or to contribute energy required for animal growth, maintenance, reproduction, and overall performance. Feed ingredients typically constitute the main nutritional foundation of animal feeds and are included at relatively high levels in the feed formulation. Whereas a ‘functional feed ingredient’ is a dietary component included at moderate levels (typically between 2% and 5%) in animal feeds to provide specific physiological, health, or performance benefits beyond basic nutritional value (Figure 1). Unlike standard feed ingredients, which primarily meet nutritional requirements, functional feed ingredients contain bioactive compounds, such as antimicrobial peptides, specific fatty acids, antioxidants, or other health-promoting substances. This concept differs from functional feed additives, which are used at lower inclusion rates and do not contribute to the feed formulation significantly. BSFL as a Functional Feed Ingredient We consider BSFL as a function feed ingredient due to the presence of various compounds such as bioactive peptides, chitin, and lauric acid (Figure 2) with antimicrobial functions. These components offer significant physiological benefits, including enhanced gut health, improved immune responses, and antimicrobial properties. However, the current economic feasibility of BSFL remains limited by high production and processing costs relative to conventional ingredients like fishmeal or soybean meal. While this cost barrier may limit BSFL’s role as a complete fishmeal substitute in the near term, our approach focuses instead on its sustainable use as a functional feed ingredient- not to replace fishmeal, but to complement plant-based diets and enhance fish performance and health at economically viable inclusion levels. Consequently, incorporating BSFL at moderate inclusion rates (~5%) rather than as a complete protein replacement represents an economically sustainable strategy, effectively leveraging its health-promoting properties while managing costs. Recent Research Findings Our recent studies investigated the effects of supplementing high-SBM diets with different forms (whole and defatted) and inclusion levels (2.5% and 5%) of BSFL in rainbow trout through a dietary feeding trial (Singha et al. 2025) and a bacterial-challenge study (Ma et al. 2025). In the feeding trial, we used six isonitrogenous (crude protein 50%) and isolipidic (20%) diets, namely fishmeal-based diet (FM), high SBM (SBM), whole BSFL at 2.5 and 5% (WB2.5 and WB5), and defatted BSFL at 2.5 and 5% (DB2.5 and DB5) supplementation in high SBM-based diets. Trout juveniles (initial weight- 5.2 g) were randomly distributed in twenty-four tanks (30 fish/tank) with four replications for each diet and fed six experimental diets at apparent satiation for 10 weeks. After the feeding trial, we investigated the effects of BSFL supplementation on growth, feed utilization, proximate and nutrient (amino acids, fatty acids, and minerals) compositions, immune-related gene expression, and intestinal histopathology (Singha et al. 2025). Additionally, fish from representative diets were transferred to Dr. Jie Ma’s lab for a bacterial challenge study after the end of the growth trial (Ma et al. 2025). The summarized outcomes of our studies are presented here. Improving growth and nutrient utilization: Trout fed a diet containing 5% whole BSFL exhibited significantly better growth performance compared to groups fed traditional fishmeal or SBMbased diets (Figure 3a). Additionally, diets supplemented with BSFL improved feed conversion ratio (Figure 3b) and protein utilization efficiency, supporting the beneficial functional role of BSFL. Improved nutrient profile of the fish: Fatty acid analysis revealed significantly elevated levels of lauric acid in BSFL- (CONTINUED ON PAGE 48) FIGURE 3. Weight gain (a) and feed conversion ratio (b) of rainbow trout fed experimental diets for 10 weeks (Source: Graphical representation from Table 5 in Singha et al. (2025)). Experimental diets: FM, fishmeal-based diet; SBM, soybean meal-based diet; WB2.5 and WB5, whole BSFL at 2.5 and 5% supplementation in high SBM-based diets, respectively; DB2.5 and DB5, defatted BSFL at 2.5 and 5% supplementation in high SBM-based diets, respectively. 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 support animal health, growth performance, and efficiency in various ways but do not necessarily provide significant nutritional value on their own.
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