Feed efficiency is a major goal for aquaculture sustainability, and selecting fish to genetically enhance this trait would be highly valuable. However, no selective breeding program specifically targeted to feed efficiency exists for farmed fish, mostly because of the difficulty of measuring individual feed intake. However, a negative phenotypic correlation between feed efficiency and weight loss at fasting has been previously demonstrated in sea bass submitted to feed deprivation (FD). We mated sea bass parents selected for their high (FD+) or low (FD-) weight loss at fasting to produce FD+ and FD- progeny, which were reared in a single tank to avoid common environmental effects. At 8 months of age, 1200 of those fish were submitted to three alternating periods of fasting (3 weeks) and re-feeding (3 weeks). Individuals were weighed at the end of each feeding and fasting period. Their line of origin was identified by genotyping of 12 microsatellite markers, resulting in 1130 unambiguously assigned fish (484 FD-, 686 FD+). FD- offspring lost significantly less weight than FD+ offspring in this feed deprivation trial. After that the feed efficiency of eight groups of 50 FD+ fish and eight groups of 50 FD- fish was evaluated in four successive 20-day periods. At the end of the fourth period, 10 fish per tank were sacrificed to evaluate their carcass yield. The FD- fish had a better overall growth and were fatter, and FD+ fish had a better carcass yield. A better feed efficiency was expected for the FD- fish, but differences between the two groups for this trait, measured either with feed efficiency ratio or with residual feed intake, were not consistently significant Although the two lines were clearly divergent for several traits, demonstration of feed efficiency differences between the FD+ and the FD- lines was not consistently observed in sea bass. A second generation of selection may allow further divergence in the lines and reveal differences in feed efficiency. (C) 2013 Elsevier B.V. All rights reserved.