International Journal of Aquaculture, 2025, Vol.15, No.5, 221-228 http://www.aquapublisher.com/index.php/ija 222 the growth and reproduction processes of aquatic organisms (Thiruvasagam et al., 2024). However, the intensive use of these inputs raises important concerns related to the sustainability of their production. According to FAO (2024), approximately 19% of fish aquaculture production is directed toward the manufacture of these ingredients, which raises significant environmental concerns, as this practice is closely linked to overfishing (Satyakumar et al., 2024) of species such as anchoveta (Engraulis ringens), the main raw material used. This fishing pressure has led to a progressive reduction in natural stocks of the species, compromising the long-term sustainability of the production chain. Given the concerns regarding the sustainability of FM and FO production, initiatives have emerged aimed at replacing these ingredients in aquaculture diets. However, such replacement presents a considerable challenge, as alternative ingredients must not only be safe for farmed organisms but also possess a nutritional composition compatible with that of traditional inputs, particularly regarding the PUFA profile, with emphasis on long-chain polyunsaturated fatty acids (LC-PUFAs), such as DHA and EPA (Zhang et al., 2024). A deficiency of these compounds in the diet can significantly impair the zootechnical performance of fish and shrimp, affecting their growth, reducing their immunocompetence, and decreasing their final nutritional value, which may negatively impact their commercial acceptance. In this context, microalgae have emerged as a promising alternative due to their high nutritional and functional value. These microorganisms are important sources of essential amino acids, carbohydrates, carotenoids, polysaccharides, and long-chain polyunsaturated fatty acids (LC-PUFAs) (Bergmann et al., 2024), in addition to containing bioactive compounds with antioxidant potential, such as flavonoids, alkaloids, glycosides, β-carotene, and phenolic compounds (Salem et al., 2022). Given this multifunctional potential, the present work aims to compile updated scientific evidence on the feasibility of using microalgae as partial or total replacements for fishmeal and fish oil in diets formulated for fish and shrimp, with a focus on nutritional and immunological aspects. 2 Effects of Microalgae Inclusion on The Nutritional Quality of Fish and Shrimp The wide diversity of microalgae species, combined with their high nutritional value, has sparked growing interest in research aimed at developing sustainable solutions. These investigations primarily seek to mitigate the environmental impacts associated with conventional aquaculture practices, particularly the intensive production and use of fishmeal (FM) and fish oil (FO) in commercial feed formulations. In this context, Sarker et al. (2020) investigated the total replacement of FO and the gradual replacement of FM using whole cells of Schizochytriumsp. and defatted biomass of Nannochloropsis oculata in the feeding of Nile tilapia (Oreochromis niloticus) over a period of 183 days. The authors observed that the fillets of fish fed with the total replacement diet (100NS) of FM and FO had a significantly higher lipid content (1.8%) compared to the control diet (commercial feed with FM and FO). Regarding amino acid composition, methionine and histidine levels were lower in the 33% replacement diet (33NS) and numerically higher in the 66% replacement diet (66NS), when compared to both the control and 100NS diets. Additionally, the levels of polyunsaturated fatty acids (PUFAs) were significantly higher in the microalgae-based diets, regardless of the replacement level, especially docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). DHA deposition in the fillet was highest in the 100NS diet (5.15 mg/g), contrasting with the lowest value observed in the control diet (2.47 mg/g). Supporting the potential of microalgae as alternative nutrient sources in aquafeeds, Karapanagiotidis et al. (2022) evaluated the replacement of FM with Chlorella vulgaris and FO with a blend of Schizochytrium sp. and Microchloropsis gaditana (SM) in the diet of Sparus aurata over 12 weeks. The results indicated that fish fed with 100% FO replacement (SM100) showed increased levels of muscle PUFAs, including linoleic acid (18 : 2n-6), γ-linolenic acid (18 : 3n-6), arachidonic acid (20 : 4n-6), adrenic acid (22 : 4n-6), and docosapentaenoic acid (DPA, 22 : 5n-6). On the other hand, SM diets with 50% and 100% replacement led to lower concentrations of n-3 PUFAs such as stearidonic acid (18 : 4n-3), eicosatetraenoic acid (ETA, 20 : 4n-3), and DPA (22 : 5n-3), compared to the control group.
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