southern grew almost as rapidly as in spring and fall. Southern species 

 had greater annual growth. Shell growth of hybrids resembled southern 

 parent more than northern. The F\ hybrid surpassed the southern parent in 

 shell growth in the third year. The two species are separated ecologically 

 in the northern part of the range on the Atlantic coast, but half way down 

 the east coast of Fla. opportunities for hybridization should be plentiful. 

 The subspecies of M. mercenaria, which is common where the two species grow 

 together, closely resembles laboratory-spawned F2 hybrids. In laboratory 

 experiments the southern species gaped within 2 4 hrs under refrigeration and 

 in 60 hrs all were gaping or dead. All northern species were alive and most 

 in good condition after 350 hrs. Less than 20% of Fi hybrids were gaping at 

 end of 350 hrs. Storage time depends on physiological condition of clams. 

 Experiments suggest that hatchery-reared hybrids might be best for planting 

 in clam farms. Satisfactory techniques for large-scale rearing of commercial 

 quantities of clams from metamorphosis to the size at which they can be 

 planted safely under protection have not yet been developed. Success of clam 

 mariculture in the Caribbean is speculative. In tropical waters spawning 

 will be more or less continuous, mitigating against successful controlled 

 spawning in hatcheries. (Abstracter's note: this paper has an extensive 

 list of literature cited.) - J.L.M. 



1283 



Menzel, Winston. 1971. 



Selection and hybridization in oysters and clams. Mollusk Chaser, South 

 Florida Shell Club, Inc., Miami, Fla. 9(10), 2 p. 



Selection is that process in which -certain alternative traits inherent in a 

 species are transmitted to the progeny. Hybridization is one way to develop 

 those traits. Two species of quahog clams occur on the east coast, Mercenaria 

 mercenaria from Canada to Florida, and M. campechiensis from New Jersey to 

 Florida, the Gulf of Mexico and the West Indies. The northern quahog can be 

 held out of water under suitable conditions for considerable periods. Annual 

 growth of the southern quahog is about twice as fast as the northern. Fi 

 hybrids have the keeping quality of the northern parent and the fast growth 

 of the southern. They must be produced in a hatchery. Various characteristics 

 could be selected for ideal clams, and certified seed could be produced. - 

 J.L.M. 



1284 



Menzel, Winston. 1971. 



The mariculture potential of clam farming. Am. Fish Farmer World Marie. 

 News 2 (8) : 8-14. 



Clams of genus Mercenaria appear to be suitable subjects for mariculture. 

 Clam farming was advocated in Massachusetts about 50 years ago, but it was 

 not until Dr. Loosanoff and colleagues at Milford, Conn, developed 

 techniques for rearing shellfish larvae that molluscan mariculture could 

 become a reality. Laboratory-spawned quahogs from that source have been 

 grown in Florida for some years. Growth was faster in these semitropical 

 waters. Northern quahog, M. mercenaria, occurs from the Gulf of St. 

 Lawrence to Florida, and sparsely in some places in northern Gulf of Mexico. 

 Southern quahog, M. campechiensis , ranges from New Jersey to Gulf of Mexico 

 and West Indies. Northern species is found in mouths of estuaries, bays and 

 inlets, in salinities above 20°/ °o. In the northern part of its range, and 

 south to about Cape Kennedy (Canaveral) southern species is found in shallow 

 waters off the coast. Below C. Kennedy southern quahog is found inshore also, 

 sometimes on same grounds as northern species. The two have differences in 

 morphology and physiology. Shells of southern quahog are more obese and 

 growth ridges are persistent on exterior of valves, even in old clams. The 

 exterior central portion of valves in northern quahog are smoothish, 

 especially in larger clams. Purplish-blue pigment characteristic of 

 northern quahog is rarely found in the southern form. Especially in larger 

 clams, the lunule of the southern species is about as wide as long, longer 



359 



