253 full-sib families from 33 males and 23 females of European seabass were produced in a partly factorial mating design. All fish were reared in the same tank during 14 months, then 7000 of them were dispatched in four farms to different locations (France, Israel, Italy, Portugal) representing a wide variety of environmental conditions. Around 400 g mean weight, 1177 to 1667 fish in each site were weighed and length was measured. Condition factor (K) was calculated. Pedigrees were redrawn a posteriori using microsatellites markers: parental origin could be retraced for 99.2% of fish. Due to a high incidence of deformities, the useful sample size was reduced to 491-670 fish per site. Maternal effects were small. Using a simple animal model, heritability of weight ranged from 0.38 +/- 0.14 to 0.44 +/- 0.14 in the different sites. Length was highly correlated to weight, with similar heritabilities. GxE interaction, estimated through genetic correlations of weight across the different environments ranged from 0.70 +/- 0.10 to 0.99 +/- 0.05. Genetic correlations between weight or length and K were not similar in the different sites. (c) 2008 Elsevier B.V. All rights reserved.