Conditions Governing Oyster Growth 99 



mature oysters is possible, are greater than those limiting 

 reproduction. The optimum has not been precisely de- 

 termined in either case. When food and temperature 

 conditions are favorable, growth apparently is most rapid 

 in water with a salinity varying from about 1.012 to 

 1.016. There may be no very narrowly limited opti- 

 mum salinity, but whatever its limits, it is possible that 

 they are not the same on all parts of the coast. 



In the matter of reproduction, also, very few experi- 

 ments have been made to determine the optimum salin- 

 ity. Some observations made several years ago indi- 

 cated an optimum much lower than that of growth, and 

 these are usually quoted. It would naturally be expected 

 that the most favorable density for growth would also be 

 best for reproduction, and recent observations confirm 

 this. Where it has been noticed by a trained observer, 

 the best set of spat occurs in water the density of which 

 varied between i.oio and 1.017. Whether or not there 

 is an optimum of narrower limits, is not known. 



Sudden changes of density, so common everywhere 

 in shallow water near the shore, are always harmful and 

 sometimes fatal. Swimming embryos, for example, are 

 often destroyed by a fall of rain. Though the resulting 

 * change of temperature may play a large part in it, it is 

 possible that the sudden change of density is also very 

 harmful. Recent experiment has proved that the trans- 

 planting of oysters to water of a different density, 

 whether greater or less, has a bad effect even when the 

 difference is slight. If the difference is considerable, 

 oysters may cease to grow or may die. These effects are 

 specially marked on mature individuals. The very young 

 attached oysters are better able to adapt themselves to 

 such changes. 



