1289 



Menzel, Winston. 1974. 



Clams and oysters as animals for mariculture in the United States. Proc. 

 10th Ann. Conf., Mar. Technol. Soc: 611-617. 



Meroenaria is relatively easy to rear under artificial conditions and brings 

 a high price, thus is a suitable candidate for mariculture. Small clams, 

 which are eaten raw, bring the highest prices, which is another advantage. 

 M. meroenaria ranges from Gulf of St. Lawrence to Gulf of Mexico and includes 

 a subspecies in the south. M. oampeohiensis ranges from New Jersey to Gulf 

 of Mexico and Caribbean, only offshore in the north. The 2 species have 

 several morphological and physiological differences. Northern quahog keeps 

 the shell closed for a considerable period when out of water, southern species 

 quickly gapes and dies. Northern species grows faster in warmer waters of 

 northwest Fla. than in its native habitat, but not as well as native southern 

 species. F]_ hybrids have the fast growth rate of southern parent and keeping 

 qualities of northern. Thus, in southern waters, the hybrid should be used in 

 mariculture. Growth under laboratory conditions is less than in the natural 

 environment. Space requirements and costs work against holding juveniles for 

 long in the hatchery. They can be planted in natural environment when as 

 small as 1 mm, but must be protected against predators. Clams have been 

 grown to market size in plots covered with wire. Below 15 mm mortality was 

 heavy, probably from predators that entered through meshes of wire. When 

 planted at over 15 mm mortality was 10 to 25%. In Fla. waters northern 

 quahog will reach market size in about 2 1/2 yrs after spawning. About 500 

 clams/m 2 was maximum density for good growth. Clams 15 mm or larger, planted 

 in fenced areas at 250 clams/m2 , and allowing for 25% mortality, will yield 

 about 2x10^ clams/ha. At a wholesale price of 3C/clam 1 ha would yield 

 $6 0,000 gross. The method used would not be practical commercially. In 

 Virginia, survival rates of 1 mm clams have been excellent when planted on 

 bottom prepared with crushed shell, gravel, or slag to reduce predation. 

 Experiments in Fla. using crushed oyster shell and pea gravel, and planting 

 2,500 small hatchery-reared clams on each of 8 plots, each 4.55 m 2 , were not 

 so successful. Half the control plots were covered with 12 mm mesh plastic 

 coated wire. In these, survival was better than 50% in 9 months. In all 

 other plots, including experimental, mortality was 80 to 100%. No 

 explanation was given for failure. Various combinations of F^ and F2 hybrids 

 and backcrosses have been tested for growth. Clams from parents selected for 

 rapid growth were larger than controls, and some reached market size of over 

 50 mm within 14 to 15 months. Commercial possibilities for clam mariculture 

 are good if all presently known techniques are used. New techniques and 

 refinements of present methods are needed. Filter-feeding mollusks are 

 superior to other mariculture organisms because, being primary consumers, 

 they waste less energy than animals at higher trophic levels. - J.L.M. 



1290 



Menzel, Winston. 1976, 



Mariculture: Hybridization and selection in clams, Meroenaria spp. ASB 

 Bull. 23(2) : 81. 



" F l hybrids between Meroenaria meroenaria and M. oampeohiensis had desirable 

 traits of both parents, faster growth rates of the southern and good keeping 

 qualities in the shell of the northern. Considerable variation in growth 

 occurred between individuals, presumably under genetic control. Hybrids 

 and backcrosses were made from original wild parents secured from Atlantic 

 and Gulf of Mexico coasts. Certain selected crosses showed about 40% faster 

 growth rates than obtained previously - to commercial size within 15 months 

 of spawning. Only limited progeny testing has been done. - J.L.M. 



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