Chinese Journal of Oceanology and Limnology Vol. 26 No. 1, P. 76-80, 2008 DOI: 10.1007/s00343-008-0076-6 Morphological and karyotypic variation in three wild populations of Meretrix meretrix* DENG Yuewen ( 邓岳文), DU Xiaodong ( 杜晓东)**, HUANG Ronglian ( 黄荣莲), WANG Qingheng (王庆恒) (Fisheries College, Guangdong Ocean University, Zhanjiang 524025, China) Received June 6, 2006; revision accepted Jan. 16, 2007 Abstract Three wild populations of Meretrix meretrix sampled from Dongxing, Beihai, and Shankou along the coast of Guangxi, China, were investigated with morphometry and karyometry. Six morphological indices (shell length, shell height, shell width, hinge length, total wet weight and shell weight) were measured. Differences in all morphological indices except hinge length were significant among the three populations (P < 0.05). The mean values of these indices (except for the hinge length) in the Dongxing population were larger than those in the Beihai and Shankou populations, although the latter had the largest hinge length. The karyotype of the Beihai, Shankou and Dongxing samples had ten metacentric, six submetacentric, and three subtelocentric chromosome pairs. No significant difference was shown in the centromeric index values of the chromosomes in the populations (P>0.05). However, the order of metacentric, submetacentric and subtelocentric chromosome pairs was variable among the three populations. The results indicate a high level of inter-population variation in morphology and karyotype. Keywords: Meretrix meretrix; population; morphology; karyotype 1 INTRODUCTION Meretrix meretrix (Bivalvia: Veneridae), an important economic species, is naturally distributed along the coastal waters of China, Korea, Japan and India. In China, the species is one of the commonly cultured bivalves with well-developed cultivation techniques. In the past decade, much attention has been paid to polyploidy induction (Chang et al., 1996; Lv et al., 2003) and culture such as seed production, hatchery and planting (Wang et al., 1993; Tang et al., 2005). Recently, the genetic structure of wild populations of M. meretrix at both allozymic and DNA molecular levels have been presented (e.g. Yan et al., 2001; Shen et al., 2003; Chen et al., 2004; Du et al., 2004; Li et al., 2006; Xue et al., 2006). Differentiation existed to some extent among the wild populations studied, demonstrating adaptive differences among genotypes (Shen et al., 2003; Feng et al., 2005), or barriers to larval dispersal (Du et al., 2004; Li et al., 2006). Chromosome karyotyping can contribute significantly to the interpretation of polygenetic relationships in shellfish species (Ladrón et al., 1996; Zheng et al., 1996; Sun et al., 2003). Population variability has been detected at the karyotypic level (Insua et al., 1994; Huang et al., 2001). Although both the chromosome number and karyotype of M. meretrix have been described (Chang et al., 1996; Wu et al., 2002; Lv et al., 2003), no information to date on its karyotype has been available in wild populations collected from different places. Additionally, high variations in morphology have been found to exist in wild populations of M. meretrix (Du et al., 2004; Feng et al., 2005). This paper describes the morphometry and karyometry of three wild populations of M. meretrix from different locations along the coast of Guangxi to evaluate population variation at both the morphological and karyotypic levels. 2 MATERIALS AND METHODS 2.1 Populations Wild animals were sampled from Beihai and Shankou and Dongxing in Guangxi for one week in May 2000, transported to the laboratory, acclimated in 1000 L banks for a few days with daily water refreshing and fed with cultured microalgae Nitzschia closterium. * Supported by the Natural Science Foundation of Guangdong Province (2002C60115) and the foundation of Guangdong Ocean University (E06031). ** Corresponding author: zjdxd@21cn.com