Astaxanthin, a carotenoid pigment found in several aquatic organisms, is responsi-
ble for the red colour of salmon, trout and crustaceans. In this study, astaxanthin production
from freshwater microalga Chlorella sorokiniana and marine microalga Tetraselmis sp. was
investigated. Cell growth and astaxanthin production were determined spectrophotometrically
at 620 and 480 nm, respectively. Astaxanthin was extracted using acetone and measured
subsequent to biomass removal. Aerated conditions favoured astaxanthin production in C.
sorokiniana, whereas Tetraselmis sp. was best cultured under unaerated conditions. C.
sorokiniana produced more astaxanthin with the highest yield reached at 7.83 mg/l in
6.0 mM in nitrate containing medium compared to Tetraselmis sp. which recorded the highest
yield of only 1.96 mg/l in 1.5 mM nitrate containing medium. Production in C. sorokiniana
started at the early exponential phase, indicating that astaxanthin may be a growth-associated
product in this microalga. Further optimization of astaxanthin production was performed using
C. sorokiniana through a 23 full factorial experimental design, and a yield of 8.39 mg/l was
achieved. Overall, the study has shown that both microalgae are capable of producing
astaxanthin. Additionally, this research has highlighted C. sorokiniana as a potential
astaxanthin producer that could serve as a natural astaxanthin source in the current market.