Heterotrophically produced microalga Asterarcys quadricellularis: A superior feed for growth and survival of the brine shrimp

Microalgae are crucial bioresources in the aquaculture industry due to their high nutritional value and bioactive components. This study compared the growth and viability of Artemia franciscana nauplii fed with a newly isolated microalga Asterarcys quadricellularis AQYS21 cultivated under photoautotrophic (PA) and heterotrophic (HT) conditions. HT cultivation, optimized with 8 g/L glucose and 4 g/L yeast extract, resulted in approximately 11.4-fold higher algal biomass productivity than PA cultivation. Feeding trials demonstrated that A. franciscana nauplii showed significantly higher growth (1.42-fold) and survival rates (1.78-fold) when fed HT microalgae compared to those fed with PA microalgae. Nutritional composition analysis of the microalgae revealed that HT cultivation led to a 3.03-fold increase in the carbohydrate content compared with the PA condition. Additionally, HT microalgae produced lower levels of chlorophyll a and carotenoids but higher levels of linoleic acid (omega-6) and oleic acid (omega-9) than PA microalgae. Amino acid analysis indicated that HT microalgae had lower amounts of proteinogenic amino acids and higher amounts of free amino acids than PA microalgae. Interestingly, HT microalgae had 1.62-fold thinner cell walls, as observed through TEM images, leading to easier digestion and absorption. This, coupled with high carbohydrate content, likely contributed to the enhanced growth and survival of A. franciscana. To the best of our knowledge, this study is the first to compare PA and HT microalgae as potential feed sources for brine shrimp. Collectively, the findings suggest that HT cultivation of microalga A. quadricellularis AQYS21 is a useful strategy for producing aquatic feed, enhancing both algal biomass productivity and brine shrimp growth.