162 MARINE FISHERIES OF NORTH CAROLINA 



development of spawn in the clam has been described in detail by Loos- 

 anoff (1937-a). Soon after spawning has ceased in the fall, the sex products 

 commence to develop, often reaching maturity by mid-winter, but because 

 of cold temperatures, spawning of the new generation is delayed until the 

 next spring. Normally the ovaries and testes are white in color, but in old 

 clams they may have a reddish or yellow tint (Kellogg, 1903). Spawning is 

 believed to be directly correlated with temperature, but other factors may 

 exert an influence making it as complicated as it is in the oyster. Belding 

 (1912) found spawning to occur in Massachusetts from mid- June to mid- 

 August, commencing at a temperature of 76° to 77° F. (23-25° C). 

 Loosanoff (1937-b) found spawning to occur earlier at about 73° F. and 

 to continue for a longer period in Long Island Sound. Studies have not 

 been conducted in North Carolina to determine the period of spawning 

 but it would be expected that spawning occurs earlier in North Carolina 

 and continues longer than it does in the north. Some practical clammers 

 and dealers believe that hard clams may spawn throughout the year in 

 North CaroHna, especially during mild winters. 



Sexual maturity in the clams occurs at a very early age. Loosanoff 

 (1943) states that young clams may spawn at an age of three or four 

 months, but the majority spawn after they reach their first year. Belding 

 (1912) found on an average, that clams must be two years old before they 

 spawn. He states that "little necks" and "blunts," or old clams, do not 

 spawn and that only the small "sharps" (2^ to 3 inches) and large clams 

 (3 to 3^ inches) spawn, although both "little necks" and "blunts" con- 

 tain varying amounts of spawn. 



The embryology and early development of the clam are similar to that of 

 the oyster. The sex cells are extruded into the mantle cavity and pass out 

 of the animal through the excurrent siphon (Belding, 1912; Loosanoff, 

 1937-b). After fertihzation of the eggs in the water, cell division occurs 

 and continues until a small mass of cells capable of swimming is developed. 

 Within 36 hours a small shelled animal called the veliger results. Increase 

 in size continues during the next 6 to 12 days, when free swimming ceases 

 and attachment of the larval clam occurs. Meanwhile, a byssal gland has 

 developed in the foot. This gland secretes a substance which hardens on 

 contact with the water to form a tough thread, called a byssus, by means 

 of which the larval clam attaches to or "sets" upon such objects as sea- 

 weed, stones, and shells. This attachment marks the transition period 

 between the free swimming stage and the beginning of the adult. 



The primary function of the byssus is believed to be protective, for the 

 young clams are liable to be covered by fine silt and mud or be washed 

 ashore during strong winds. Attachment in a suitable location thus protects 

 the small clams and affords them an opportunity to grow to a size when 



