Figure 25 Dead shells of Plnctada mazatlanlca . Inner sides are moderately 



overgro\ini by fouling organisns and shell substance not eroded. 



pearl oysters. Pron my personal observations and from the infonaation given by the fisher- 

 3en, I conclude that predators are not a serious factor in the lives of pearl oysters in 

 PanaEia, and that the depletion of the oyster population cannot be attributed to depredation 

 by these enemies. 



The relatively larre number of dead oysters fo\md in Coiba Channel probably 

 represents the accuiitilation of shells during a period of years. These groxmds \/ere known 

 to be productive, and in past years attracted many fisherr.en. Dead shells probably failed 

 to attract attention v/hen live oysters were abundant, but v;hen they declined in abundancSt 

 each dead shell became conspicuous. 



There is, of couxse, a possibility that a disease reduced the population of 

 oysters to its present state. In order to ejcplore the r.erits of this assunption, I have 

 nade a nicroscopic er.anination of oyster tissue, vfith special attention to the presence of 

 parasites and other pathological evidence. Because of the scarcity of living oysters, 

 this exar:iination \ras not as ertensive as I should like to have it. 



Microscopic era'nination of tissues of pearl oyster 



Every live oyster brought in by the diver v/as dissected, and its tissues exajained 

 within 2k hours after its removal frou. the sea. Ov;in£ to crowded conditions and lack of 

 adequate laboratory facilities aboard the ship, the examination of live tissues v/as rather 

 brief. It v/as limited to the inspection of principal organs, and examination of blood 

 snears and preparations of snail pieces of excised tissues. 



On v/ind;/ da^^s, the laboratory work v/as impossible, and had to be postponed until 

 more favorable conditions prevailed. Altogether, 25 oysters were dissected and examined in 



Ul 



