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

Ensis siliqua is regarded as an increasingly valuable ¢shery resource with potential for commercial aquaculture in many European countries. The genetic variation of this razor clam was analysed by randomly ampli¢ed polymorphic DNA (RAPD) in six populations from Spain, Portugal and Ireland. Out of the 40 primers tested, ¢ve were chosen to assess genetic variation. A total of 61 RAPD loci were developed ranging in size from 400 to 2000 bp. The percentages of polymorphic loci, the allele e¡ective number and the genetic diversity were comparable among populations, and demonstrated a high level of genetic variability. The values of Nei's genetic distance were small among the Spanish and Portuguese populations (0.0510 .065), and high between these and the Irish populations. Cluster and principal coordinate analyses supported these ¢ndings. A mantel test performed between geographic and genetic distance matrices showed a signi¢cant correlation (r 5 0.84, Po0.05), suggesting an isolation by distance process.

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