THE SHELLFISH INDUSTRY 301 



remains stagnant and in summer becomes very hot and, by 

 evaporation, very salty, conditions which result in a 

 tremendous increase in the microscopic plant life, notably 

 diatoms, which forms the ideal food for the oysters which 

 are laid on the bottom of these claires. These grow and 

 fatten at an exceptional speed and soon reach a remarkable 

 size, when they are taken out of the claires and placed in 

 stone tanks, known as " bassins de d6gorgement," con- 

 taining fresh, clean sea water in which they are left for 

 several days in order that they may become thoroughly 

 cleansed internally (Plate 108). The water is then run 

 off, the outsides of the shells brushed clean, and the oysters 

 are packed ready for transport. 



It is in the claires at Marennes that the well-known 

 green oysters are produced. These obtain their colour, 

 which has become known as Marennin, from a particular 

 diatom named Navicula fusiformis var. ostrearia. Although 

 there is no discernible difference in taste, these green oysters 

 are considered a delicacy in many places and command 

 a high price. 



Originally the native oyster was exclusively cultivated 

 in France but of recent years it has been almost completely 

 ousted in the more southern beds by the Portuguese oyster 

 of which the vast majority of oysters reared at Arcachon 

 or fattened at Marennes now consist. The Portuguese 

 oyster obtained its footing in France in a peculiar manner. 

 A cargo of these oyv^^ters, considered to have gone bad, was 

 thrown overboard near the mouth of the Gironde, but 

 apparently some at least recovered, for a number of years 

 later a large and flourishing bed of Portuguese oysters 

 was discovered on the spot where the supposed rotten 

 cargo had been thrown overboard. In the more northern 

 beds, mainly on the north and south coasts of Brittany, 

 the native oyster is still cultivated. It suffers however. 



