Proceedings of the Third World Fisheries Congress: Feeding the World with Fish in the Next Millenium—The Balance between Production and Environment

Growth Comparison between Triploid and Diploid Pacific Oyster during the Reproductive Season

Zhaoping Wang, Yun Li, Ruihai Yu, Qiang Gao, Chuanyuan Tian, Xiaodong Zheng, Rucai Wang


Polyploid shellfish have become a high-priority research area worldwide because of their merits (e.g., sterility and fast growth) since Stanley (1981) succeeded in inducing triploidy in the American oyster Crassostrea virginica. Polyploidy has been studied in nearly 30 shellfish species (reviewed by Beaumont 1991), and polyploid breeding in shellfish has been highly regarded in China. In 863 projects, studies on polyploid breeding in Pacific oyster Crassostrea gigas, Chinese scallop (farreri scallop) Chlamys farreri, pearl oyster Pinctada martensii, and abalone Haliotis discus hannai Ino were done simultaneously, and many breakthroughs were obtained. Now, triploid breeding in oysters has developed into an industry in coastal China. Triploid mollusks grow more quickly than diploids in almost all species studied, including American oyster (Stanley et al. 1984), bay scallop Argopecten irradians (Tabarini 1984), Pacific oyster (Allen and Downing 1986), nobilis scallop Chlamys nobilis (Komaru and Wada 1989), pearl oyster (Jiang et al. 1991), and Chinese scallop.

The energy-reallocation hypothesis was first proposed to explain the increased growth in triploids (Purdom 1972). Triploid Pacific oyster and bay scallop being larger than diploids around the time of sexual maturation (Tabarini 1984; Allen and Downing 1986; Jiang et al. 1991) support the energy-reallocation hypothesis. But the hypothesis does not explain cases in which triploids are significantly larger than diploids before sexual maturation (Lyu and Wang 1992; Guo and Allen 1994a, 1994b; Liang et al. 1994).

Pacific oyster is the most important marine culture species in China. Its reproductive season is from June to mid-August in the coastal area of Shandong, and its peak spawning time usually is the first 10 days of July. In this study, we tested the energy-reallocation hypothesis by comparing the growth of diploid and triploid Pacific oyster during the reproductive season.

One-year-old Pacific oysters were sampled from Sanggou Bay in Rongcheng, Shandong Province. Triploid oysters were induced by inhibiting the release of the second polar body in the fertilized eggs using 6-dimethynolaminopurine (6-DMAP) (referred to as the treated group). The triploid rate was 60% as measured by a flow cytometer. Diploid oysters served as the control group.

More than 50 individuals were sampled randomly every 2 weeks during the 1999 reproductive season from the control and treated groups. Shell growth was measured with a vernier caliper. The maximum intervals from the umbo to the edge of the shell, from the anterior extremity to the posterior extremity of the shell, and from left shell to right shell were measured as height, length, and width, respectively. Tissue weight and whole body weight were measured with an electronic scale. The ploidy of oysters in the treated group was checked individually with a flow cytometer.

The growth measurements of shells in the control and treated groups are listed in Table 1. Analysis of variance (ANOVA) analysis indicated no significant difference in shell height between the control and treated groups (P > 0.05). However, oysters in the treated group were significantly larger than the controls in shell length and width (P < 0.05). These results suggest that growth in triploid oyster is stereoscopic.