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

Chromosome Manipulation of Mollusks in China

Guofan Zhang, Huayong Que, Xiao Liu, Fusui Zhang, Fanxiu Wu


The production of marine mollusks in China has reached approximate 8 million metric tons, accounting for 81% of the national total output of mariculture. With economic development, the products from traditional molluscan aquaculture hardly meet the growing consumer demand for high-quality proteins. Improvements in the commercial traits of mollusks (e.g., production and growth) are expected to be obtained through biotechnology. Moreover, biotechnology may provide solutions to the problems arising from aquaculture. Before the 1970s, triploids were applied mainly to control of the population quantity in aquatic animals such as fish (Lou 1984). The pioneering work by Stanley et al. (1981) demonstrated the advantage of the commercial characteristics of triploid mollusks, which triggered the intensive research of molluscan triploidy starting in the 1980s.

This major effort contributed to the use of triploids in commercially important marine species. Triploids have various distinguished advantages in commercial traits compared with the diploid siblings. Triploids are sterile. Sterility often leads to fast growth, richness in glycogen, and higher survival rates during the reproductive season. Triploids in some species, such as Pacific oyster Crassostrea gigas, provide marketable products throughout the year. To date, based on available data, triploid induction has been conducted in 24 species of marine mollusks (21 species of bivalves and 3 species of gastropod; Table 1).

Research on polyploids progressed rapidly in recent years. Several favorable factors promoted the progress:

• molluscan artificial breeding technology has reached a level of maturity;
• the reproductive characteristics of mollusks have provided a unique opportunity for chromosome manipulation;
• the application potential of polyploid mollusks is attracting considerable attention from both academic researchers and aqua-cultural industry farmers.

In China, the exploitation of triploids in several species—Pacific pearl oyster Pinctata martensii, Chinese scallop (Zhikong scallop) Chlamys farreri, and Pacific abalone Haliotis discus hannai Ino—has been listed in the National Hi-tech Research and Development Plan (863 Plan). All these species possessed an important position in the Chinese mariculture industry. Advances have been made to various extents in these projects, with some reaching mid- or large-scale production (Zhang et al. 1998, 2000a, 2000b).

Triploids can be produced by two means: direct and indirect. In general, direct induction has been widely accepted in hatcheries. However, the current methods have several disadvantages:

• the induction procedure is relatively complicated, and its efficiency varies greatly depending on many environmental factors;
• triploid induction must be repeated every year;
• treatments lead to the abnormal development of abundant larvae; and
• effective induction methods are expensive, and low-cost methods produce triploids with variable and low proportions.

Therefore, the more effective induction methods await future development and the direct induction methods are currently being optimized. With the recent breakthrough of tetraploid Pacific oysters, investigation of new effective methods of triploid induction (e.g., triploids can be indirectly produced by mating tetraploids and diploids) has intensified.