148 MARINE FISHERIES OF NORTH CAROLINA 



Within one day a complete animal with a shell and all necessary organs is 

 developed. Gradual changes in size and shape of the larval oyster take place 

 through approximately two weeks, after which the oysters cement them- 

 selves to various objects by means of a secretion from a gland in the foot. 

 The attachment ends the free-swimming state of the oyster, and locomotive 

 structures, such as the foot and swimming organ, disappear. 



SETTING. The period of attachment or setting of the larval oysters is most 

 important to the industry. At this time, shells or similar materials are 

 scattered about to provide a solid substrate to which larval oysters may 

 attach themselves. After the set or "spat" (as the young oysters after attach- 

 ment are called) have been secured, the oystermen may transplant them to 

 more favorable locations or allow development to an adult or marketable 

 size to take place where attachment occurred. 



Through microscopical examinations of water samples for the presence of 

 larval oysters the period of setting can be accurately predicted. This informa- 

 tion is of value when heavy sets are desired in order to have the shells or 

 other collectors function most efficiently. Indiscriminate planting of shells, 

 too early or too late in the season, may result in the shells becoming covered 

 with various animal and plant life or with fine sediment, or failure of the 

 oysters to secure the necessary substrate. Many studies have been made on 

 the periods and intensities of setting. A comprehensive review of the litera- 

 ture on the subject was recently prepared by Korringa (1940). 



RATE OF GROWTH. The rate of growth varies considerably with the locality 

 and environmental factors. Salinity, food conditions, temperature, chemical 

 constituents, type of bottom, and probably heredity all play an important 

 role in controlling growth. Moore (1904) states that in South Carolina 

 oysters not more than six or seven months old may reach a length of 2>4 

 inches, and in some warm sounds of North Carolina an oyster may grow to 

 i^ inches in length in from two to three months. In the southern states a 

 marketable sized oyster of from three to six inches may grow in less than 

 three years. In northern areas, it may require four to seven years for oysters 

 to reach the same size. An unusual growth rate was recently noted in North 

 Carolina waters. Oysters which had set on shells planted in Bay River, a 

 tributary of Pamlico Sound, during the summer of 1947 were found to be 

 three to four inches long after 18 months. Information on periods and rates 

 of shell growth are important in determining the most favorable times when 

 oysters can be transplanted. 



TEMPERATURE. Temperature plays an important role in the physiology of 

 feeding, respiration, spawning, and shell growth, and has a direct bearing on 

 the sanitary control of the industry. Experimental studies by Galtsoff (1928) 

 have shown that at temperatures of5°C. (4i°F.) and below, oysters cease 

 to function normally in their feeding and growth and go into hibernation. The 



