62 March 2009 tat used by young game and forage fish species. Concentrated predation by larger fish may positively or negatively affect future sport fish population balance in a pond or lake. Beneficial predation may occur when carnivorous fish are reduced over abundant forage. However, excessive predation of young game and forage fish could limit food availability to larger fish and delay their recruitment into the fishery. Predators, such as water snakes, fish eating birds and river otter may prey more readily on concentrated fish populations confined in shallow water. Aquatic plants and filamentous algae may have more shallow water habitat, less than 1 m in depth, to extend their growth and increase density during low water levels. Increased vegetation growth in shallow water may interfere with fish feeding, seining and sport fishing activities. Ponds filled with aquatic plant and algae growth may increase the habitat in which small game and forage fish species hide and avoid predation by larger fish. Such conditions could contribute to an overabundance of small fish and cause a future imbalance in pond fish populations. Lake managers may struggle to control aquatic vegetation growth in shallow waters. Contact herbicides and algaecides should be used with care to prevent chemical toxicity to fish and to avoid oxygen depletions. Note 1 State Extension Specialist for Aquaculture, Kentucky State University Aquaculture Program, Graves County Extension Office, 251 Housman Street, Mayfield, KY 42066; Tel: 270-247-2334; E mail: fwynne@email.uky.edu References Boyd, C.E. 1990. Water Quality in Ponds for Aquaculture. Alabama Agricultural Experimental Station, Auburn University, Auburn, Alabama. USA Mattinson, M.R. and L.S. Glasscock, editors. 1997. Ponds – Planning, Design and Construction. Natural Resources Conservation Service, Agricultural Handbook 590, United States Department of Agriculture, Washington D.C. USA. Pearl Culture thys molitrix), bighead carp (Aristichthys noblis), mandarin fish (Siniperca chuatsi) or freshwater shrimp (Macrobrachium nipponense). The mussel mainly grazes on plankton for food; the more plankton in the water, the more rapid growth of the mussel and production of better freshwater pearls. So, pearl ponds need to be fertilized to increase plankton blooms. However, fertilization leads to eutrophication. Chinese freshwater pearl culture needs to improve pearl quality and reduce water pollution resulting from the manuring practiced in pearl culture. A bio-promoter containing calcium and other mineral elements is used to promote mussels to secrete nacre to gain good quality pearls. Pearls are divided into nucleus pearls and non-nucleus pearls. Almost all of marine pearls are nucleus pearls. Freshwater pearls are mainly non-nucleus pearls, which account for more than 90 percent of all freshwater pearls. Non-nucleus pearls are formed by inserting cell slices manufactured by the out membrane of the mussel. Generally, it takes 3-5 years to produce a marketable pearl. The sizes of freshwater pearls are unequal and the small size pearls accounts for the greater part of production. This affects the total average price of the freshwater pearl. Actually, the high quality freshwater pearls are equal to the saltwater pearl. In the last few years, as the output of freshwater pearls increased, the nucleus pearl has developed more quickly. Nucleus pearls are formed by inserting the nucleus manufactured from the shell of the mussel or other stiff materials. It takes 1-2 years. Because the freshwater mussels are larger, the types of nucleus pearls are many, for example, button pearls, cross pearls, Buddha pearls and men pearls. The most important factor that limits freshwater nucleus pearls is high mortality of the mussel after inserting the nucleus into the mussel. To improve the quality of the mussel and change the method of insertion are two ways to solve this problem. The primary color of freshwater pearls is white and those account for more than 60 percent of all output. Other colors include orange, red, green, black and purple. Pearl color relates to the host mussel, the cell slices inserted and the minerals in the water. Many companies that manage freshwater pearl culture, process and trade in China. The main companies include Shanxiahu Group, Ruanshi Company, Qidazhou Company, Shanshui company and Suzhou United Pearl Company. Most of the pearls on the mainland were exported through Hong Kong 10 years ago. Now, more and more pearls are exported directly to other countries. Many Chinese pearl companies have their own pearl culture sources. They play an important role in the development of pearl culture by solving the problem of disease, the improvement of water quality and the extension of good strain of mussels. Notes 1Aqua-life Science and Technology College, Shanghai Fisheries University, Shanghai, 200090, P. R., China. References Chen L. S. and J. L. Li. 2007. Study on Pearl Market in China. Fisheries Science & Technology Information 34(2): 76-78. Ge X. P., G. F. Zhang and Y. X. Zhou. 2002. New Technology of Freshwater Pearl Culture. Shanghai Science and Technology Press, Shanghai, China. Li J. L. 2007. Exploitation and protection of germplasm resources of freshwater pearl mussel. Scientific Fish Farming 6:1-2. Li J. L. and Z. Y. Bai. 2007. New variety of freshwater culture----Kanglebang mussel. China Fisheries 10:44-45. Li J. L., Z. G. Dong and Y. S. Li. 2007. Alien Aquatic Animal and Plant in China. Shanghai Science and Technology Press, Shanghai, China. Zhang, G. F. 2005. Culture of freshwater pearl. Agriculture Press, Beijing, China. (Continued from page 60)
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