Background Scenedesmus species can synthesize beneficial nutrients such as protein and lipids, which exert positive effects on the growth and disease resistance of aquatic animals. However, photoautotrophic cultivation of Scenedesmus species currently suffers from low biomass and target product yields. Therefore, it is essential to ascertain the optimal cultivation mode for maximizing biomass accumulation and the yields of target products.

Objective This study aims to screen for suitable cultivation methods that support efficient growth and the synthesis of high-value nutritional components in Scenedesmus species, thereby facilitating their development and application in aquatic feeds.

Methods In this study, Scenedesmus sp. SS-303 was selected as the experimental microalga, internal transcribed spacer (ITS) sequencing tool was adopted for microalgal species identification. Subsequently, biomass, glucose and urea consumption from the medium, algal cell size, and the contents of lipids, proteins, fatty acids, and amino acids in Scenedesmus sp. SS-303 were compared and analyzed under three cultivation modes (photoautotrophy, heterotrophy, and mixotrophy).

Results The algal strain was identified as S. bijugus via ITS molecular identification, and it has been named as S. bijugus SS-303. Microalga by the mixotrophic mode achieved a biomass of 18.98 g/L (dry weight) that was significantly higher than that of the heterotrophic group (12.95 g/L) and the photoautotrophic group (1.25 g/L), with larger algal cell size. It could fully utilize glucose and urea, showing the highest nutrient utilization efficiency. In terms of nutritional components, the contents of protein (41.46%), essential amino acids (16.92%) and total amino acids (34.88%) in the mixotrophic group were remarkably higher than those in the other two groups. No significant difference was observed in lipid content among the three groups. The photoautotrophic group had the highest content (14.98%) of α-linolenic acid (C18:3ω-3), while the heterotrophic group had the highest content (12.73%) of linoleic acid (C18:2ω-6). Carotenoid contents in photoautotrophic and mixotrophic groups were significantly higher than those in the heterotrophic group. Compared with previously reported algal strains, S. bijugus SS-303 presented high yields of biomass, protein, lipids, essential fatty acids and essential amino acids 2710.00, 1123.57, 804.06, 122.70, and 190.11 mg/(L·d), respectively under mixotrophic culture conditions.

Conclusion Mixotrophy is the optimal cultivation method for S. bijugus SS-303, which can simultaneously achieve high biomass production and synthesis of high-quality nutritional component. These findings provide theoretical basis and technical support for the high-value utilization of this alga in aquaculture industry.