Conditions Governing Oyster Growth 97 



ago in North Carolina and in the Chesapeake, indicated 

 that reproduction practically ceased when the tempera- 

 ture during the breeding season fell below 60 Fahrenheit, 

 and that the swimming stage was rarely reached when 

 the water was warmer than 80. But it is probable that 

 the minimum temperature at which reproduction is pos- 

 sible is nearer 70 than 60, and it takes place in water 

 above 80 in certain parts of the Gulf of Mexico. If the 

 facts were known, it might possibly be found that there 

 were variations in minimum, optimum, and maximum 

 temperatures, oysters having accommodated themselves 

 to the varying conditions in different localities. 



Because of danger from frost or ice, oysters are not 

 left in very shallow water where the winter temperature 

 is low. Young oysters, especially, are susceptible to ex- 

 treme cold. 



Though a determination of the salinity of the water, 

 and a systematic observation of its variations, would be 

 of value to oyster culturists, few have interested them- 

 selves in the subject. It is nearly as easy to observe 

 salinity as temperature. All that is necessary is a simple 

 case containing two glass floats (Figure 24), with hollow 

 bulbs so weighed that in distilled water, each sinks until 

 the surface of the water reaches the zero point on a 

 scale borne in the stem. The density of distilled water 

 is read i.ooo. 



The salt in solution in sea water prevents the float 

 from sinking to so great a depth as this. If the water, 

 in a test case, reaches the numeral 9 of the scale, the 

 density is read 1.009. This scale measures densities 

 from i.ooo to i.on. The second float bears a scale 

 registering densities ranging from i.oio to 1.021, the 

 range for both covering variations likely to be found 



