International Journal of Aquaculture, 2025, Vol.15, No.5, 221-228 http://www.aquapublisher.com/index.php/ija 224 Based on the studies presented, there is a clear convergence regarding the potential of microalgae as viable and sustainable alternatives to traditional sources of fishmeal (FM) and fish oil (FO) in aquafeeds. This substitution has gained prominence not only due to its ecological appeal but also because of the ability of microalgae to provide key nutrients, such as polyunsaturated fatty acids (PUFAs) and essential amino acids, although some nutritional limitations remain. In the study by Sarker et al. (2020), for example, the total replacement of FM and FO with Schizochytriumsp. and Nannochloropsis oculata resulted in a significant increase in DHA levels in tilapia fillets, demonstrating the efficiency of these microalgae in supplying beneficial lipids. However, variations in amino acid composition particularly the reduction in methionine and histidine levels in certain diets point to a specific nutritional limitation of these sources, suggesting the need for targeted supplementation. In the investigations conducted by Karapanagiotidis et al. (2022), although an increase in n-6 PUFA levels was observed following FO replacement, there was also a reduction in n-3 fatty acids such as ETA and DPA. This raises concerns regarding the nutritional value of the fish flesh from a human consumption perspective. These results suggest that the lipid composition of microalgae must be carefully balanced to avoid imbalances between omega-3 and omega-6 fatty acids an essential factor in determining the nutritional quality of farmed fish. In this context, the study by Seong et al. (2021) adds an important dimension to the discussion by demonstrating that combining different species of microalgae (Nannochloropsis, Schizochytrium, and Chlorella) was more effective in promoting adequate levels of n-3 PUFAs, including long-chain PUFAs (LC-PUFAs), in Pagrus major. These findings suggest that synergistic interactions between microalgal species may compensate for individual nutritional deficiencies, representing a promising strategy for developing more complete feed formulations. In the case of shrimp, the findings of Pakravan et al. (2017) and Allen et al. (2019) reveal a dose-dependent response to substitution: intermediate inclusion levels (25%) of Spirulina platensis, for example, were the most effective in increasing concentrations of beneficial fatty acids. Furthermore, replacement with Schizochytriumsp. led to an increase in DHA content but also a reduction in EPA levels, again reinforcing the importance of lipid balance in diet formulation. Finally, the study by Li et al. (2022) reveals a critical limitation: the total replacement of FM with Chlorella sorokiniana significantly impaired the essential amino acid profile in shrimp, resulting in a considerable reduction in their nutritional value. This finding underscores the need for a careful assessment of the protein quality of microalgae, with particular attention to the amino acid profile in formulations with high inclusion levels of these biomasses. In addition to the nutritional assessment, it is essential to analyze the impact of partial or total replacement of fishmeal (FM) and fish oil (FO) on the immunological parameters of fish and shrimp, as well as to investigate the potential antimicrobial activity that microalgae may exert against organisms with pathogenic potential. 3 Microalgae in Aquaculture: Ommunomodulation, Antimicrobial Activity, and Antioxidant Effects Studies have shown that the inclusion of microalgae such as Spirulina platensis, Chlorella vulgaris, Nannochloropsis spp., and Haematococcus pluvialis in diets with reduced fishmeal (FM) and fish oil (FO) promotes positive effects on immune parameters. For example, in experiments with Clarias gariepinus and Carassius auratus, the partial replacement of FM by Spirulina sp. and Chlorella sp. resulted in significant increases in red and white blood cell levels, hematocrit, hemoglobin, and expression of the genes TLR2, IL-1β, and TNF-α, as well as improved survival rate after challenge with Aeromonas hydrophila (Raji et al., 2018; Cao et al., 2018). Similarly, in Nile tilapia (Oreochromis niloticus), the replacement of 15% to 20% of fishmeal by Nannochloropsis oculata led to increased lysozyme activity, higher IgM (immunoglobulin) concentration, greater protection against infection byA. hydrophila, and preservation of intestinal integrity (Salem et al., 2022).
RkJQdWJsaXNoZXIy MjQ4ODYzNA==