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The supply of microalgae to hatcheries is a limiting factor for the mass larval production of sea cucumber ( Apostichopus japonicus) in Fujian Province, China. In this study, Nannochloropsis sp. isolated from the East China Sea was tested as food for A. japonicus larvae. The first trial compared the effect of mono-, bi- and trialgal diets comprising three microalgae ( Chaetoceros muelleri, Dunaliella tertiolecta and Nannochloropsis sp.) on A. japonicus larval growth, survival, settlement and juvenile growth. The results showed that there were no significant differences in survival and settlement between larvae fed with Nannochloropsis sp. and other diets. All diet treatments yielded similar juvenile sea cucumber output. In the second trial, A. japonicus larvae were fed equally four times daily at three different rations (5000, 20 000 and 40 000 cells mL−1 day−1). Larvae fed 20 000 cells mL−1 day−1 were significantly larger than larvae in other groups and experienced the highest survival rate. In the third trial, A. japonicus larvae were fed 20 000 cells mL−1 day−1 in three different frequency (2, 3 and 4 meals day−1). The greatest body length was observed in larvae that received 3 meals day−1. Survival and settlement of larvae fed 2 meals day−1 were significantly lower than other two groups. These results suggest that Nannochloropsis sp. can be used as a diet for the large-scale production of A. japonicus seed, and larvae fed three times daily at a ration of 20 000 cell mL−1 day−1 are recommended for hatchery production of A. japonicus. [ABSTRACT FROM AUTHOR]