Ž . Aquaculture 193 2001 39–48 www.elsevier.nlrlocateraqua-online Negative correlation between aneuploidy and growth in the Pacific oyster, Crassostrea gigas: ten years of evidence Alexandra Leitao a , Pierre Boudry b , Catherine Thiriot-Quievreux a, ) ˜ ´ a ObserÕatoire Oceanologique, UniÕersite P. et M. Curie — CNRS — INSU, BP 28, ´ ´ 06230 Villefranche sur-Mer, France b Station IFREMER, Laboratoire de Genetique et Pathologie, BP 133, 17390 La Tremblade, France ´´ Received 25 March 2000; received in revised form 10 July 2000; accepted 18 July 2000 Abstract This study unites previous and new observations that chromosome loss in somatic cells of juveniles of the Pacific oyster Crassostrea gigas is associated with reduced growth rate. New data were obtained from four hatchery-produced progenies. Within each progeny, oysters of identical age were sampled and classified as fast-growing or slow-growing according to their shell length, or live weight. Chromosome numbers were individually scored from 30 randomly chosen metaphases from gill tissue. Although the diploid chromosome number in C. gigas is 2 N s20, hypodiploid cells of 2 N s19, 18 or 17 were observed in all progenies. The difference in percentage of aneuploidy between fast- and slow-growing oysters ranged from 5% to 22% and Ž 2 . was highly significant. In one progeny, a highly significant negative correlation R s0.58 was observed between individual level of aneuploidy and growth performances individually recorded under common controlled conditions. The consistency of the negative relationship between growth rate and aneuploidy was obvious in all populations studied between 1988 and 1999. However, when comparing aneuploidy between fast- and slow-growing oysters, two different groups of populations can be clearly distinguished. The question remains to determine the cause of these differences. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Aneuploidy; Growth; Chromosome; Oyster; Crassostrea gigas ) Corresponding author. Tel.: q 33-4-93-76-38-25; fax: q 33-4-93-76-38-93. Ž . E-mail address: thiriot@obs-vlfr.fr C. Thiriot-Quievreux . ´ 0044-8486r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. Ž . PII: S0044-8486 00 00488-9