SHELLFISH 97 



preserved the next stage is to extend the area of the 

 natural beds. This involves a knowledge of the con- 

 ditions of depth, temperature, salinity and character 

 of bottom that are necessary to the successful growth 

 of the oyster. Finally the productivity of an oyster 

 " park " and the quality of its produce can be greatly 

 improved by providing artificial " stools " for the recep- 

 tion and development of the spat. Many substances 

 can be used for this purpose. The Romans used 

 earthenware tiles, and similar tiles are used to this day 

 in France. Brushwood, trees, stones and stakes, and 

 old oyster shells (cultch) are also used. 



The earthenware tiles used in France are hollowed 

 on one side to receive the spat, and are coated with lime 

 to facilitate the removal of the oysters when they are 

 a year old. They are then from \ to 1 in chin diameter, 

 and are picked off the stools and placed on stands 

 where they are thinned out from time to time as they 

 grow. 



The chief oyster fisheries in Britain are at Whitstable, 

 Colchester and Bright lingsea. Nearly 40,000,000 

 oysters were gathered on the coasts of England and 

 Wales in 1920, and were sold for about 250,000. 



Perhaps the next most important edible bi-valve is 

 the mussel. Frequently, mussel beds are situated near 

 the mouth of rivers, and consequently tend to be con- 

 taminated by sewage. It has been established by 

 various investigators notably Dr. Klein and Professor 

 James Johnstone that mussels are able to cleanse 

 themselves of sewage pollution in a comparatively short 

 time if they are re-laid in sterilized water. Experi- 

 ments on a large scale have been carried out with the 

 mussel beds at the mouth of the Conway river since 

 September, 1916. The mussels are gathered from the 

 beds and placed about two deep on wooden grids in a largp 



