FISHERY RESOURCES OF THE PHILIPPINE ISLANDS. 93 



accurate information regarding the age and growth of shells obtained 

 from direct observations and measurements is very desirable. 



Mr. Seville Kent states in regard to the rate of growth of the pearl 

 oj'ster : 



Under favorable conditions a period not exceeding three years suffices for the 

 shell to attain to the marketable size of 200 to 230 millimeters (8 or 9 inches) 

 in diameter, and heavy shells of 2.3 kilos (5 pounds) weight per pair may be the 

 product of five years growth. 



' The food of the pearl oyster consists of minute marine infusoria, 

 DiatomaceWj etc. We discovered that in fully 75 per cent of the specimens 

 examined, the food consisted of Diatomacece with a small amount of 

 vegetable matter. 



The pearl oyster' does not travel to any great distance; in fact, after 

 the spat stage;, it remains in one spot for the greater part of its life, 

 although it can^ and does at times, cast off the byssus attachment and 

 reattach to some more desirable place, moving very slowly by means of 

 its small foot. The very old shells of M. maxima Jamson were, with 

 but few exceptions, without attachment, probably the weight of the shell 

 being sufficient to keep them in place. 



ENEJIIES OF THE PEAllL OYSTER. 



The pearl oyster, especially in its younger stages, is exposed, to 

 constant danger. Numerous fishes consider it a great delicacy, and 

 such fish are found in large numbers about the pearl banks. The various 

 species of sharks, rays, sparoides, and balistes feed largely upon shell 

 fish, including the pearl oyster. However, these are not wholly an evil, 

 as they are probably the intermediate host for the cestode which is the 

 cause of the growth of pearls ; the fish becoming infested with this cestode 

 by eating the oyster. Doubtless, star fishes also cause much destruction 

 to the banks, and, in old specimens, the boring sponges, boring worms, and 

 gastropods, do great damage. 



In addition to these enemies which affect the oyster directly, there are 

 an enormous number of marine animals and plants that, by using up 

 the available space and food which otherwise would fall to the lot of the 

 pearl oyster, affect the life of the oyster indirectly. 



One pearl diver reported the finding of a very large pearl bank south 

 of Basilan Island, where the shells were abundant and of very large size, 

 but of no value, as they were dead and had lost their luster. In cases of 

 this kind, it is almost impossible to state the cause of the destruction. 

 It may have been brought about by some epidemic due to the crowded 

 condition of the shells, or possibly by some volcanic disturbance, or a 

 dozen other causes might be assigned, but without facts it is useless to 

 theorize on the subject. 



