ARTIFICIAL PROPAGATION OF OYSTERS. 5 



a garden hose. For retaining the larvae when 10 days old, fine 

 monel metal screen was used and proved quite satisfactory for use 

 in salt water. 



SUCCESSFUL METHOD OF HATCHING AND REARING YOUNG 



OYSTERS. 



In order that the various important factors affecting the artificial 

 propagation of the oyster may be clearly understood, a i^-sume will 

 first be made of the method that proved successful in hatching and 

 rearing the young oysters. The brood stock of adult oysters used 

 for producing spawn consisted of native oysters grown at Milford 

 and soutliern oysters planted there by the bureau in 1919. These 

 oysters were planted on shallow inshore beds in Gulf Pond, where 

 the warm temperatures would mature them for spawning at an early 

 date. 



Numbers of the large oysters were placed on trays in the spawning 

 tank, and the temperature was gradually increased until the water 

 was filled with the spawn ejected by tlie adults (see fig. 3). Im- 

 mediately after spawning had ceased, the oysters were removed and 

 the eggs allowed to develop to the swimming stage in the warm 

 water. Then the embryo oysters were transferred to the rearing 

 tanks, and when supplied with running water they developed shells 

 in 40 to 48 hours. The use of a mechanical agitato-r at this time 

 helped greatly in bringing about a natural and rapid development 

 of the oyster larvae. For retaining the embryos a combination 

 filter of loose, fine sand and filtros was used until the embryo oysters 

 had reached tlie shell stage. From that time on the larvse were 

 held in by the filtros blocks of various gi'ades, which were changed 

 to suit the growth and size of the forms. When the larvse were 10 

 days old, or older, they were held in by means of fine monel metal 

 screens, which permitted an unusually good flow of water. 



After a period of from 15 to 20 days tlie larvas were ready to " set," 

 and collectors of various materials were placed in the tanks for their 

 attachment. In the first successful test over 150 spat were found 

 " set " on the collectors, and in the last over 1,000 spat became at- 

 tached (see fig. 4) . The loss in numbers from the countless eggs pro- 

 duced by the adult oysters was traced to mechanical defects in making 

 the filters fit closely and not to a mortality of the larvse. After the 

 spat had grown for a day or two in the rearing tanks they were 

 transferred to favorable places in the harbor, where a maximum 

 growth might be obtained. The care of the oyster after attachment 

 is easily accomplished by the modern methods of culture. 



REPRODUCTION AND DEVELOPMENT. 

 SELECTION OF THE OYSTERS. 



The adult oysters used for the production of spawn were taken 

 from the inshore beds early in the summer and from the deep-water 

 offshore beds later in the season. In this way it was possible to 

 obtain mature spawn from oysters in Long Island Sound from early 

 in July until September, as the genital products of the oysters in 

 the warm, shallow waters mature earlier than those of oysters in 

 deep water. 



