-■I 



1] ounce by the former. This disparity continued toiucrease more slowly thereafter, 

 but unfortunately for want of data we cannot give the exact amount for the age of 4| 

 years. 



It is a pity that we have not available a record of the yearly weight increase of 

 the oysters fished on the Ceylon Muttuvaratu Par in the same years as those of the 

 Tolayiram Par. If we had I think we should hud that there would be shown close 

 approximation between the two ; the Muttuvaratu oysters of that generation were 

 markedly stunted and poor and the fishery of 1SS9 was decided upon only after 

 considerable hesitation. 



The only datum I possess is the weight given above of three typical oysters from 

 the 1891 fishery. This which is equivalent to a weight of 179 L6 ounces for 10 

 shells at 6| years of age as against 17 - 64 ounces for a similar number of 6f years old 

 oysters from the Tolayiram Par in 1890 indicates practical identity in growth-rate. 



By the courtesy of Captain Carlyon I have been enabled to measure a few indivi- 

 duals of this last fished generation of Tolayiram Par oysters and append a table 

 thereof in which the measurements of some of the oysters from the Muttuvaratu 

 Par are included for the sake of comparison. The numbers are too restricted to 

 give an average that may be taken as thoroughly trustworthy. They constitute, 

 however, the only data available and till systematic records extending over a consider- 

 able series of years be obtained by work in the future it is well to place them on 

 record : — 



Date. 



Age. 



Size. 



Average. 



March 1B35 



1J years .. . . | 



40 X 64 X 23 Millimetres 

 60 X 53 X 22f 



"I 66 X 58-5 X 22-75 







62X58X23* 



1 



April 1886 



2| years . . 



63 X 58 X 27J 

 67 X 61 X 31 



I 63-5 X 70-5 X 27-5. 





r 



62 X 62 X 30 



71 X 70 X 32 „ 



J 

 1 



October 1S8 7 



4 4, years 8 , 



79 X 70 X 32 „ 



76-66 X 71-33 X 33. 







80 X 74 X 35 „ 



J 







77 X 80 X 32 ,, 



] 



November 18S8 



5 A years . > . . ■ 



78X78X33 



f 76-66 X 77-33 X 32-83. 







78 X 74 X 33i 



March 18S9 



5 J years . . 



78 X 80 X 33 



80 X 74 X 31 „ 



] 79 X 77 X 31-33. 





" 



72 X 6S X 31 



1 



„ 1890 



6J years . . 



70X73X34 



72-66 X 71 X 32-16. 





<- 



76 X 72 X 31£ 



J 







Muttuvaratu Par, Ceylon. 





r 



i 



6^ years (deep short 

 oysters covered with 



1 

 1 





1 



living growths — 



1 73 X 63 X 36 Millimetres 



" 



March 1891 . . . . ^ 



Lithothamnion and 



S>67 X 57 X 35| 



73-33 X 59 33 X 35-83. 





corals ; much corro- 



1 80 X 58 X 36 ,, 







ded by the tunnel- 







I 



ling of Clionej. 



J 





It would appear from the preceding tables that the growth of the Indian oysters 

 is distinctly retarded after the third year, the life conditions being more favourable 

 to the young than to the old — a condition which I believe will be found due largely to 

 the great abundance of encrusting organisms, sponges and polyzoa especially, which 

 begin to flourish upon the valves of the Indian oysters in wonderful abundance from 

 the age of li year. A similar state of marked retardation in growth is charac- 

 teristic of the oysters from the Ceylon South M oderagam Par, after the attainment of 

 the same age, a retardation coincident with the appearance of luxuriant sponge,, 

 tunicate, and polyzoa growth upon the valves. On the South Cheval where such 

 commensal growth is rare, no such marked slackening in the rate of growth is 

 apparent.* 



The oysters of the Tolayiram Par in October 1887, when 4J years old, gave a 

 pearl valuation of but Es. 3-11-5 per 1,000 and as this was much too low to justify 

 a profitable fishery, it was not till after the valuation of November 1888, affording a 

 Valuation of Es. 18-12-8 per 1,000, that a fishery was decided upon. The oysters 

 were therefore 5f years old when first fished in 1889. 



* See my "Report on the Biological results of the Ceylon Pearl Oyster Fishery of 1904", Ceylon Marine 1 

 Biological Keports, No. 1, Colombo, 1S05. 



