Figure 6. — Biologist Inducing out-of-season spawning of oysters and clams under laboratory conditions. 



oysters by shipping them, early in May, to 

 Boothbay Harbor, Maine, where the water 

 temperature is considerably cooler than in 

 Long Island Sound. Oysters so kept can be 

 induced to spawn any time between mid- 

 August and late November, thus providing 

 normal sex products which then are unobtain- 

 able from Long Island Sound oysters. 



By use of the two above-described methods 

 of advancing and delaying gonad development, 

 spawning of the Eastern oyster can be induced 

 any time of the year. As a result of these dis- 

 coveries, much more can nowbe accomplished 

 in the field of spawning and propagating oysters 

 and Sonne other species of commercial mol- 

 lusks. 



The conditioning methods described above 

 are not equally successful with all groups of 

 the Eastern oyster. This is probably because 

 populations of this species are not genetically 

 alike, but consist of different physiological 

 races. Some experiments in this field strongly 

 support this assumption by demonstrating that, 

 even though all these oysters belong to the 

 sanne species, the temperature requirements 

 for gonad development and spawning of the 



northern populations are definitely lower than 

 for the southern group. In some of these 

 experiments it was possible in winter to induce 

 spawning of 50 percent of Long Island Sound 

 oysters after only 18 days of conditioning at 

 about 71° F., while 78 days were needed to 

 achieve the same results with New Jersey 

 oysters. Oysters of the more southern groups, 

 kept under conditions identical with those 

 applied to northern oysters, failed, as a rule, 

 to produce 50 percent spawners. 



Eggs and Larvae 



Fertilized oyster eggs vary in diameter 

 from about 45 to 62 microns, but the majority 

 measure between 50 and 55 microns. Amicron 

 is one twenty-five thousandth of an inch and is 

 designated by the Greek letter "//". The size 

 of an egg is not influenced by the size of the 

 mother oyster; for example, eggs discharged 

 by females measuring over 9 inches long 

 averaged 50.4//, while eggs from younger and 

 smaller females only 3 to 4 inches long aver- 

 aged 51 // . 



12 



