Background/Objectives: Microalgae are gaining increasing attention as sustainable sources of dietary lipids and other bioactive compounds; however, the relationship between microalgae lipid composition and physiological outcomes in vivo remains insufficiently understood. This study aimed to characterize antioxidant activity, total lipid content and fatty acid (FA) profiles of selected freshwater microalgae and to evaluate their dietary impact using Drosophila melanogaster as a whole-organism model. Methods: Four freshwater microalgal species (Chlorella vulgaris, Nannochloris limnetica, Scenedesmus communis, and Tetradesmus obliquus) were cultivated separately in 3N-BBM+V medium under controlled laboratory conditions. DPPH, FRAP and TPC were measured in microalgae methanolic extracts. Total lipids were extracted using a modified Breuer method and quantified gravimetrically. FA profiles were determined as fatty acid methyl esters by GC-FID. Freeze-dried microalgal biomass (3 mg/mL) was incorporated into standard D. melanogaster diet. Lifespan and body mass were assessed separately in females and males, as well as fecundity in general. Results: Total lipid content ranged from 17.3% to 28.1% of dry weight, with FA profiles dominated by C16 saturated, monounsaturated (omega-9), and omega-6 polyunsaturated fatty acids. Correlation analysis indicates that antioxidant properties of the studied microalgae are more closely linked to lipid fractions than to phenolic content. Dietary supplementation with microalgal biomass of three out of four microalgal species significantly extended median lifespan, particularly in males, without adverse effects on body mass or fecundity. Conclusions: These findings indicate that freshwater microalgae can serve as a physiologically safe dietary lipid source. D. melanogaster represents a suitable in vivo model for screening the nutritional potential of microalgal lipids.

Microalgae are seen as a promising source of sustainable essential lipids for animal and human nutrition. These advantages, however, differ depending on the strain and growing conditions. Furthermore, the link between microalgae lipid profile and their effect on target organisms during dietary consumption is still not well understood. This study examined the lipid content and antioxidant properties of four microalgae strains cultured on 3N-BBM+V medium, and the effect of their dietary inclusions on the lifespan, body mass, and fertility of the common fruit fly Drosophila melanogaster. It was shown that C. vulgaris, N. limnetica, S. communis, T. obliquus exhibit total lipids at 26.7 ± 2.8%, 27.2 ± 0.9%, 16.6 ± 3.0%, and 22.6 ± 0.9% of dry biomass, respectively. All microalgal species produced unsaturated C15:0, C16:0, monosaturated C18:2n6 (omega-6), and C18:1n9 (omega-9) but at different proportions. Feeding D. melanogaster with C. vulgaris, S. communis, or T. obliquus biomass at 3 mg/mL inclusion extended the female median lifespan by 45.9%, 8.1%, and 27.0%, respectively. A more significant extension was observed for fly males, where adding biomass of C. vulgaris, N. limnetica, S. communis, and T. obliquus increased the lifespan of the flies by up to 75.0%, 25%, 29.2% and 50.0% re-spectively. The fertility of flies fed with T. obliquus and S. communis was also increased by 20% and 18% respectively. Meanwhile, no significant difference in the body mass of flies fed with microalgae was detected compared to the control.