18 



The temperature of the water probably has a definite rela- 

 tion to the time of spawning of the oyster. Artificial fertiliza- 

 tion can be best brought about when the temperature of the 

 water is from 70 to 75 degrees, and the growth of the embryo is 

 most rapid when the temperature is a little above these limits, 

 AVhen the temperature falls below 65 degrees development almost 

 ceases, and this fact may be the real explanation of the great 

 mortality among oyster fry when there is a cold rain during the 

 breeding season, 



SALINITY OF THE WATER. 



Oysters are found in water ranging in density from 1.002 

 to 1.025, but the lower densities are always injurious, and usually 

 fatal if the oysters are subjected to them for any length of 

 time. It is not possible to suecessfuily maintain oyster beds 

 in water Avhere the density is less than 1.007 during the greater 

 part of the time, for even if the oysters are not killed they will 

 be of poor condition, pale, watery and tasteless. The salinity 

 over the best beds varies from 1.010 to 1.022 ; the former being 

 the density over beds in shallow water, the latter being found 

 only over beds which are situated in M^ater of considerable depth. 

 It has been suggested that the favorable results which have 

 been noted from beds situated in brackish water may be due 

 to the fact that in these instances the water is usually shallow 

 and consequently warmer. The higher temperature, in so much 

 as it tends to increase the food supply, being considered as 

 perhaps of more importance than the salinity. 



The apparatus used for determining the salinity of the 

 water consists of a glass float made with a long, narrow stem 

 above and with a large bulb below. The bulb is weighted so 

 that in fresh Avater it sinks the instrument to a point on the 

 stem marked 1.000. 



The stem is graduated to read from 1.000 to 1.031, the fig- 

 ures representing the specific gravity; that is, they show the 

 weight of the sample of water, an equal volume of fresh water 

 being supposed to weigh 1.000. In practice the salinometer floats 

 are made in sets of three, for convenience in handling. The first 

 reads from 1.000 to 1.011, the second from 1.010 ot 1.021, and 

 the third from 1.020 to 1.031. The sample of water of which 



