Successful bivalve larval growth and survival depend on stored reserves provided by diet. The aim of this study was to evaluate the effects of microalgal diet on growth, survival, together with biochemical and fatty acid composition during larval development in grooved carpet shell (Ruditapes decussatus). Four mono- and multi-species diets were tested: (1) Isochrysis galbana, Pavlova lutheri and Chaetoceros muelleri (1:1:1, IPC); (2) I. galbana, P. lutheri and C. muelleri (1:1:2, IP2C); (3) I. galbana and P. lutheri (1:1, IP); (4) C. muelleri (C). Our results showed that feeding regime greatly influenced larval growth and survival, as well as biochemical and fatty acid composition. Higher growth and survival rates were observed in the IPC, IP2C and C diets, which all include C. muelleri. Despite the fact that the larvae fed with IP exhibited the lowest length at settlement and survival, they stored more total lipids than any of the diets including C. muelleri. The IP and IPC diets exhibited a higher percentage of total lipids, whereas IP2C and C showed a higher proportion of proteins. Lipid and carbohydrate concentration in these diets negatively affected growth and growth and survival of the larvae, respectively. Protein content of the larvae was however positively related to larval survival, whereas lipid content of the larvae negatively affected growth. Fatty acid (FA) profile of neutral lipids (NL) and polar lipids (PL) of 22-day-old larvae clearly reflected the FA proportion of each diet. Dietary DHA and DHA in NL of the larvae were negatively related to larvae growth. DHA incorporation into PL in larvae fed with DHA-deficient diets was compensated by an enrichment in EPA, 18:0dma, 22:5(n-3) and 22:2 non-methylene-interrupted dienoic FA. According to these results, the presence of C. muelleri in the diet seems to promote better growth and survival of R. decussatus larvae.