Background Isochrysis sp. is a fast-growing alga rich in polyunsaturated fatty acids such as docosahexaenoic acid (DHA) and stearidonic acid (SDA), as well as high-value pigments like fucoxanthin, and holds potential for both carbon sequestration and emissions reduction and the development of high-value products. However, significant differences exist among algal strains from different sources in terms of carbon sequestration efficiency and the ability to accumulate high-value products. The lack of systematic comparison and screening has hindered the development and utilization of superior algal strains.

Objective This study aims to screen for superior Isochrysis strains that possess both high carbon sequestration efficiency and the potential to synthesize high-value products, thereby providing algal resources for large-scale production and the development of functional feed.

Methods Four Isochrysis strains (I. galbana FJ-1, Isochrysis sp. H29, Isochrysis sp. 8701, and Isochrysis sp. PK) as study subjects. The strains were cultured for 12 days under continuous 5% CO₂ supply, and their growth characteristics, urea nitrogen utilization, pH changes, biochemical composition, pigment accumulation, fatty acid composition, and CO₂ fixation parameters were systematically compared.

Results The results showed that I. galbana FJ-1 exhibited the best overall performance. After 12 days of cultivation, its cell density reached 8.40 × 10⁶ cells/mL, biomass was 0.48 g/L, and the CO₂ fixation rate was 27.63 mg/(L·d); the contents of lipids, chlorophyll, and fucoxanthin were 27.32%, 12.74 mg/g, and 20.78 mg/g, respectively, all of which were the highest among the four strains; SDA and DHA accounted for 11.51% and 5.31% of total fatty acids, respectively.

Conclusion I. galbana FJ-1 possesses strong carbon sequestration capacity and the ability to simultaneously accumulate multiple high-value products. Its fucoxanthin content exceeds that reported in many previous studies, making it an excellent algal strain with high development potential. It can serve as an excellent algal resource for the subsequent large-scale production of high-value products and the development of functional aquatic feed.