REPOPULATION 143 



The physiology of a fishpond consists of two operations 

 emptying and filling ("faire deboire" et "faire boire"). 

 To empty the pond the sluice-gate is raised about 2| 

 inches some two hours before the tide is high. This 

 produces a current running from the pond to the sea ; 

 a somewhat feeble current, which strains through the 

 meshes of the "inner frame," and invites the young 

 fish and fry of the Arcachon basin to enter the pond. 

 When the level is the same in the basin and in the fish- 

 pond the sluice-gate is completely raised. Then, the sea 

 continuing to rise, a current flows from the sea into the 

 pond, which is " made to drink." During this operation 

 the speed of the current, often very considerable, will 

 draw a few more fry into the pond. As for those which 

 have already entered, and the adults contained in the 

 pond, they are prevented from leaving by the barrier 

 formed by the conical " sleeve." Finally the sluice-gate 

 is closed. The ponds are thus partially emptied and 

 refilled from the middle of April to the ist of November, 

 twelve days in the month and twice a day. 



These fishponds are inhabited only by surface fish ; 

 principally bar, whose fry appears at the end of July, 

 white mullet (at the end of March), black mullet, big- 

 headed mullet, jumping mullet (June to the end of 

 September), the common gilt-head, eels, conger, and 

 sometimes soles. In 1786 sardines were common in the 

 fishponds of Arcachon. These various species of fish 

 feed on insects, crustaceans, and algae. The mullet are 

 particularly fond of a plant known as ruppelle. In 

 winter they are forced to take refuge in the "deeps," 

 as the level of the water is lowered until the " shallows " 

 are left dry. In spring and summer the "shallows " are 

 submerged. The shallowness of the water allows it to 

 become heated by day and cooled by night ; the fish can 



