ARTIFICIAL PEOPAGATION OF OYSTERS. 9 



Artificially grown spat that set on sea-scallop shells placed in the 

 rearing tanks on August 2, 1923, attained an average growth of 27 

 mm. (l^'e inches) in two months. Some of the others, wliich set 

 on August 18, 1923, were kept in the rearing tanks, while the rest 

 were placed in the harbor. The average growth, for a period of 

 three weeks, was 12.5 mm. for those in the harbor and 14 mm. for those 

 kept in the tanks (see fig. 4) . The temperature of the running water 

 in tlie tanks was generally higher than that found in the harbor and 

 undoubtedly accounts for the better growth. In one year the oysters 

 attain an average length of 3 inches and width of If inches when 

 placed on inshore beds in Milford Harbor. In two years they can 

 l>e taken up for the half-shell trade, and measure on the average 4;^ 

 inches in length and 2f inches in width, and are much deeper. This 

 rapid development occurs only on the inshore flats where food is 

 abundant and the temperature of the water is high. On the deep- 

 water beds of the Sound it requires about four years for an oyster 

 to attain a length of 4 or 5 inches, or a marketable size. 



FACTORS OF ENVIRONMENT. 

 TEMPERATURE. 



The temperature of the w^ater during the development of the 

 oyster from the egg to the spat is of considerable importance. It is 

 undoubtedly the greatest influence in determining the rate at which 

 growth and development take place and is coincident with the suc- 

 cess of the experiments. The life processes of the egg, embryo, and 

 larval oyster are hastened by a high temperature and retarded by a 

 low one. A violent change or extreme high or low temperature will 

 kill the young oysters or considerably impair their vitality. Several 

 attempts were made to hasten the development of larvae by keeping 

 the temperature from 80 to 85° F., but this invariably resulted in 

 a total loss of the forms. In the successful experiments the tem- 

 perature ranged from 65 to 75°, and was kept as near 70® as possible. 



DENSITY OF AVATER. 



The water used for rearing the larvse was pumped on the flood 

 tide and had a density ranging from 1.019 to 1.0218 during July and 

 August. Just how great an influence the density of the water has on 

 the oyster embryos can not be stated, though it seems probable that 

 any considerable change in this respect would be detrimental to such a 

 delicate organism. Changes in density and temperature are closely 

 correlated so that it is hardly possible to state the exact influence of 

 either without allowing for the other. Due to the supply of fresh 

 water from the land the density of the water in the harbors and on the 

 inshore beds is generally lower than that found offshore, and when 

 within a range of density between 1.011 and 1.022 is most suitable 

 for oyster growth. 



LIGHT. 



A comparative study of conditions in the rearing tanks that were 

 placed in the simlight with those that were kept in indirect light 



