effect on some odour and texture parameters. Instru- mental measurements of flesh colour and mechanical resistance confirmed these data from sensory analysis. In larger fish, selection affected the same sensory parameters and also odour. doi:10.1016/j.aquaculture.2007.07.121 Cytogenetic characterisation of Crassostrea gigas × C. angulata F1 hybrids: Restriction enzyme digestion chromosome banding and comparison of the aneuploidy levels of the two taxa and their hybrids A. Leitão a,b , R. Chaves a , F.M. Batista b,c , S. Santos a , H. Guedes-Pinto a , P. Boudry d a Departamento de Genética e Biotecnologia, Centro de Genetica e Biotecnologia da Universidade de Trás-os- Montes e Alto Douro, CGB/UTAD, P-5000-911 Vila Real, Portugal b Instituto Nacional de Investigação Agrária e das Pescas-INIAP/IPIMAR, CRIPSul, Av. 5 de Outubro, 8700-305 Olhão, Portugal c Instituto de Ciências Biomédicas Abel Salazar- ICBAS, Universidade do Porto, Largo Prof. Abel Salazar, 2, 4099-003 Porto, Portugal d Institut Français de Recherche pour l'Exploitation de la Mer-IFREMER, Laboratoire de Génétique et Patho- logie, 17390 La Tremblade, France The taxonomic status of the two commercially important cupped oysters, Crassostrea angulata, the Portuguese oyster and Crassostrea gigas, the Japanese oyster has long been questioned. The recent observa- tion of the hybridization between C. gigas and C. angulata and the production of fertile F 1 s led us to search for cytogenetic evidence of both parental genomes in the interspecific hybrids. The cytogenetic characterisation of the hybrids was performed by restriction endonuclease treatment, which has recently shown the potential for individual chromosome identification by banding in oysters. Chromosomes of C. gigas, C. angulata and their hybrids were treated with two different restriction enzymes (ApaI and HaeIII). These chromosome markers allowed the parental haploid sets identification in the hybrids. The analysis of the banded karyotypes of the interspecific hybrids showed that for each chromosome pair, one of the homologues presented a banding pattern consistent with that of C. gigas and the other presented one consistent with that of C. angulata. These cytogenetic results substantiate the reported interspecific hybridization between C. gigas and C. angulata. The aneuploidy levels (phenomenon for which a negative relationship with the growth rate was previously put in evidence for C. gigas) were also studied for both interspecific hybrids and parental species. In view of these results and taking into account the present expansion of C. gigas aquaculture in southern Europe, the question of the need for preservation of pure C. angulata stocks should be raised as only a few populations remain in the south of Spain and Portugal. doi:10.1016/j.aquaculture.2007.07.122 Identification and characterization of QTL markers for growth traits in Kuruma shrimp P. japonicus R.E. Lyons a , L. Dierens a , N.P. Preston b , P. Crocos b , G. Coman b , Y. Li a a CSIRO Livestock Industry, QBP, 306 Carmody Rd., St. Lucia, QLD, Australia 4067 b CSIRO Marine and Atmosphere Research, Cleveland 4163, Queensland, Australia The detection, characterization and use of quantita- tive traits loci (QTL) have significant potential to improve the efficiency of selective breeding of farmed shrimp species. Following the initial isolation of molecular markers in the Kuruma shrimp P. japonicus, CSIRO has progressively identified and characterized QTL markers for growth traits in this species. An F 2 full- sib family of P. japonicus was used for the identification of the QTL markers. A two-stage selective genetic mapping strategy was applied and a total of 401 AFLP markers, following the Mendelian segregation ratio of 1:1, were generated from the population of 102 progeny. Forty-three linkage groups were obtained for the male map and thirty-one for the female map, in comparison to the haploid number of 43 chromosomes of P. japonicus. The QTL analyses using both interval and composite interval mapping methods identified two marker regions on the male map that had significant effects (16% and 7% of phenotypic variation respectively) on the growth traits (weight, carapace length and total length). Following the QTL analysis we have focused on characterizing the AFLP marker region and identifying candidate genes responsible for the traits. Using inverse PCR, 2000 bp of genomic DNA sequence around the AFLP marker was obtained and showed high homology to a fatty acid elongase gene in Drosophila and Mouse. S284 Abstracts / Aquaculture 272S1 (2007) S238–S321