Although the actiology of swimbladder inflation anomalies in important aquaculture species such as European sea bass D. labrax is not fully determined, culture conditions are commonly suggested as main contributory factors. Little information is available on whether swimbladder inflation has a genetic basis for its expression too. In this work, 24 full-sibling sea bass families from a 4 dams x 6 sires factorial crossing were reared under communal conditions. The larvae developing normal and abnormal (uninflated or hyper-inflated) swimbladders were genotyped at four microsatellite loci, Labrax-3, Labrax-13, Labrax-17, Labrax29, and allocated to the individual breeders. Out of 273 offspring, 97% could be assigned to a single parental pair. The genotype and pedigree analysis showed an imbalance in family size due to differential survival of larvae with normally inflated swimbladders, with the offspring generated from one dam and one sire being two- to three-fold superior to the other parents, respectively. In larvae with non-inflated swimbladder, significant differences in family size were observed only among half-sibling sire families, whereas in larvae with hyper-inflated swimbladder such differences were found both among half-sibling sire and dam families. The results suggest that paternally and maternally inherited factors may contribute to the expression of swimbladder anomalies in sea bass along with major environmental clues. (c) 2007 Published by Elsevier B.V.