44 SPOLIA ZEYLANICA. 



under close and accurate observation, and spawning centres will be 

 establislied in all parts of the lake. 



The following is an indication of the main lines which future work 

 at Lake Tamblegam should follow. 



Distribution. — ^Yearly systematic inspections, similar to the one 

 described in this report, should be made ; and based upon the 

 results of these inspections charts showing distribution of living 

 oysters and dead shells should be drawn up. For purposes of 

 comparison such charts would be extremely useful. 



Ager — By having these regular annual surveys much information 

 about the condition of the beds might be obtained. Thus a fall of 

 spat could be detected and the subsequent development of the bed 

 of oysters determined. From these records it would be an easy 

 matter to compute the age of the oysters on any particular bed. 



Rate of Groivth. — By taking measurements of oysters recorded at 

 the various stations it would be possible with successive inspections 

 to determine the average rate of growth. After a sufficient number 

 of observations had been made it will be possible to correlate age 

 and size. This knowledge would be of great practical value. 



Age of Maturity. — ^This could be determined by an examination of 

 the reproductive organs, and correlating this with the age and size 

 of the oyster. 



Spawning Period. — The evidence with regard to tliis should be 

 derived from three sources : — 



(1) Frequent examinations, to determine the ripeness of the 



gonads. 

 (3) Frequent tow nettings, to find out the period of the year 



when the Placuna larvte occur in the plankton. 

 (3) Determining the probable date of spatfalls. 



In addition to the above, some protection of the oysters against 

 the unreasonable rapacity of man must be ensured. This is parti- 

 cularly important in the case of adult oysters with ripe gonads. In 

 an ordinary case the problem would be a comparatively simple one, 

 and would merely require a knowledge of the spawning period of the 

 oyster, and protection could be afforded by establishing a close 

 season during that period, and also by the formation of a few reserve 

 areas. In the case of the windowpane oyster at. Tamblegam, 

 however, the stress of weather from May to January practically 

 makes diving during those months prohibitive, and fishing is neces- 

 sarily confined to the first five months of the year. Hence there is a 

 natural close season extending over more than half the year, so that 

 Hornell's recommendation that the fishing season should be limited 

 to the period between January 15 and May 15 is perfectly sound, 

 although made without any knowledge of the spawning period of 

 the oyster, but merely on the local conditions of weather. Even 

 should it be shown upon further investigation tlxat spawning takes 



