熊本牡蛎多嵴和无嵴品系F_1生长性状的群体选育

Population selection for growth in two strains of the Kumamoto oyster Crassostrea sikamea

为了改良熊本牡蛎(Crassostrea sikamea)生长性能,以多嵴品系和无嵴品系熊本牡蛎为材料,以壳高为指标,按照10%留种率,采用截头法进行了两个品系的群体选育研究,结果表明:选择反应及现实遗传力随着个体增大而增加,且多嵴品系选择反应略高于无嵴品系。对于多嵴品系而言,幼虫期、稚贝期、养成的选择反应及现实遗传分别为0.33±0.04、0.19±0.02,0.46±0.03、0.26±0.02,0.63±0.11、0.36±0.07;无嵴品系的分别为0.30±0.04、0.17±0.02,0.43±0.03、0.25±0.02,0.58±0.10、0.33±0.06。经过1周年的养成,多嵴品系和无嵴品系的壳高遗传改进量分别为8.41%、7.71%。由此可见,两个品系的现实遗传力相对较高,说明存在着一定程度的遗传变异。研究为熊本牡蛎遗传改良及新品系培育提供了理论与实践基础。

The Kumamoto oyster （Crassostrea sikamea） is an important wild oyster resource in Southeast Asia, including China, Japan and Korean. They are not only distributed naturally in China, but also live in abundance over a wide geographical distribution, ranging from Jiangsu to Guangxi, and Hainan Island. Traditionally, this species is a wild fishery resource; farmers capture these oysters from the reef or stone on the inter-tidal zone. Al-though the artificial breeding of this oyster was successfully conducted, but no relative information for genetic improvement was found. Selective breeding is the genetic manipulation of a cultured species for the purpose of improving specific traits of interest to humans. A variety of approaches have been taken in the study of the genetic breeding of mollusks, including Mendelian genetics, quantitative genetics, and cytogenetic and molecular genetic studies. However, not all of these approaches have contributed equally to the immediate development of geneti-cally improved strains. Classically, population selection indicates the method of selection for the offspring bred by free mating among individuals with superior phenotypic traits in the majority from populations of original species according to the selective breeding objective via a comparison and appraisal between the original species and local species. Due to its simple operation and easy promotion, it has been widely used in the improvement of plant and animal species. Through continuous population selection, better cultivated species with rapid growth, strong stress resistance, high meat rate and high yield can be obtained. To improve the growth trait, response to selection and realized heritability for shell height was evaluated using the many radial rib line （Stock M： a number of ribs of left shell≥6） and the non-radial rib line （Stock N： a number of ribs of left shell=0） of the cultchless Kumamoto oyster in southern China. The shell height of Kumamoto oyster was considered to be a growth characteristic due to the positive association between shell height and yield. Truncation selection was conducted by selecting the largest 10% oyster from two stocks as parents for selected groups, while the equal number parents were randomly chosen as control groups before the removal of parents for truncation selection. Progeny from four groups were cultured the identical environmental conditions at larvae, spat and grow-out stage. Genetic index increased with oyster growth, strain M showed slightly higher response to selection and realized heritability than strain N during the whole history life. For strain M, response to selection and realized heritability were 0.33±0.04, 0.19±0.02 for lar-vae, 0.46±0.03, 0.26±0.02 for spat, and 0.63±0.11, 0.36±0.07 for grow out stage, respectively. The response to selection and realized heritability of Strain N were 0.30±0.04, 0.17±0.02 for larvae, 0.43±0.03, 0.25±0.02 for spat, and 0.58±0.10, 0.33±0.06 for growing out stage, respectively. At the end of 360 day, current genetic gain was 8.41% for Strain M, 7.71% for Strain N, respectively. The relatively high realized heritability has been obtained from the two strains, suggesting that there existed a degree of genetic variation between selective and control lines of this species. Our results clearly demonstrate that population selection can effectively improve growth trait and it is a promising way to Kumamoto oyster aquaculture.