24 CEYLON PEARL OYSTER REPORT. 



The respective increases during the first two annual intervals are as follows : 



It will be noted that while the growth of the Modragam and of the South-east and 

 South Cheval oysters has been greater and more rapid than that of those upon the 

 Western Cheval, the Modragam oysters, growing more quickly than those of the 

 South-east and South Cheval up to the age of 14; to 1|- years, and thereby attaining 

 larger size, suffered retardation in the rate of increase thereafter, making but 

 7'51 millims. X 9'66 millims. X 3'00 millims. increase, whereas the South-east and 

 South Cheval oysters made 1271 millims. X 11 "41 millims. X 6'86 millims. in the 

 same period, and so reduced the disparity in size caused by the more rapid growth of 

 the Modrap-am individuals at the earlier age so much so that the difference between 

 them at the age of 2^ to 2\ years is but 1*56 millims. X 3"00 millims. X 0'04 millim. 



This lends support to our previous statement (this Report, Part I., 1903, p. 136) 

 that shell growth is most vigorous during the first two years of life, or, as we may 

 now put it, up to the size of about 60 millims. X 54 millims. X 24 millims., and that 

 thereafter it slackens to a very slow rate, actually coming to a stand, or even retro- 

 grading as regards height and length in the case of the stunted oysters of the 

 Muttuvaratu and the Mid-west Cheval. 



As examples of this slowness of growth in older oysters we may take those fished 

 this year from the South-west Cheval. These were the most vigorous and freely 

 grown as regards the general average, and yet the increase made from November, 

 1902, to March, 1904, was but 5 31 millims. in depth by 377 millims. in length, i.e., 

 between the ages of say 3^- to 3 J and 4^- to 4f years (size in November, 1902, was 

 71 '25 millims. X 65 "39 millims.). Contrast with this the increase within the same 

 period (16 months) when the oyster is younger, say between the ages of \\ to l-j- 2 - 

 and 2\ to 2^ years. In the case of oysters of this age from the South Cheval, the 

 increase has been, as shown above, as much as 16 '5 5 millims. X 13 - 64 millims., and in 

 the case of the North-west Cheval 13'69 millims. X 13*04 millims. a remarkable 

 difference indeed. 



Again we see that the disparity of growth is most marked during early life up to 

 the age of 2 years so that oysters situated in exceptionally favourable conditions 

 attain such dimensions that they are liable to be credited with greater age than 



