8 



U. S. BUREAU OF FISHERIES. 



various collectors are placed in the tanks previous to the setting stage 

 and become quite evenly covered with the spat. The number of spat 

 desired on any particular collector can be regulated by the length 

 of time they are left in the tanks and by observing the numbers that 

 have become attached from time to time. 



GROWTH OF SPAT. 



The growth of the oyster spat after " setting " is quite rapid under 

 favorable conditions. Observations made in 1922 of the growth 

 from the time of setting showed that in 13 days the spat attained an 

 average size of one-fourth of an inch (6 mm.) when placed just 

 below the surface of the water. The daily average sizes (maximum 

 diameters) of set measured in August, 1922, are given below in 

 millimeters : 



(larval shell 



Just attached 

 only) 0. 83 



1-day-oId spat . 402 



2-day-old spat . G03 



3-day-oId spat . 737 



4-day-old spat 1. 005 



5-day-old spat 1. 139 



l)-(lay-ol(l spat 1. 27:s 



Average 

 diameter 

 in ma* 



14 

 13 

 12 

 IX 

 10 



8 

 7 

 6 

 5 

 4 

 3 

 2 



1 



7-day-old spat 3 . 675 



8-day-()ld spat 2. 144 



9-day-old spat 2. 680 



10-day-old spat 3. 216 



18-day-old spat 6. 000 



18-day-old spat 10. 000 



23-day-old spat 14. 000 



Number of days old« 



Fig. 5. — Average rate of growth of spat after setting, from August 2 to August 25, 1922, 

 Milford Harbor, Conn, a, Size of spat at time of setting. 



