282 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



Change of density has an important efl'ect upon the spawning of 

 oysters. At St. Jerome Creek, Dr. Ryder found that the eggs could 

 not be impregnated in a density much exceeding that in which the 

 parent animals live. With oysters raised in water ranging from 1.007 

 to 1.0095 it was found that the milt was killed by a density greater 

 than 1.013, the individual spermatozoa losing their mobility in a few 

 moments when exposed to the greater density. The frequent failure 

 of oysters to spawn in the season in which they are transplanted is 

 perhaps in a measure owing to this cause. In Chesapeake Bay they 

 are usually transplanted from deeper, denser water to more shallow 

 and less dense, and when taken from the Chesapeake to Long Island 

 Sound they go through a similar experience. There is at the same 

 time, however, usually a change in temperature, and doubtless both 

 factors combine to produce the effect noticed. 



It has been suggested by Lieutenant Piatt that the density of the 

 water has an effect on the distribution of the set; that is, the specific 

 gravity of the swimming embryo is such that it can not sink in 

 dense water and therefore must become attached in marginal beds 

 between tide marks, as is seen on the "raccoon" oyster-beds of South 

 Carolina. 



In some places it has been found that the best results in oyster- 

 culture are to be had in brackish water, and Dr. Ryder suggests that 

 this may be largely due to the fact that water of the lower densities 

 is usually shallower, and consequently warmer and better adapted to 

 the production of an abundant supply of the minute organisms which 

 constitute the principal source of the oyster's food. There can be no 

 doubt, however, that the eastern oyster is distinctively a brackish- 

 water form. It has been found that it will not thrive in French waters 

 perfectly adapted to the culture of the European species, and there is 

 reason to believe that it will reproduce itself in a lower density than is 

 necessary for the native oyster of California. 



For determining the temperature and the density of sea waters the 

 apparatus shown in plate ii is used. It consists of a glass float with a 

 long stem and a large bulb, weighted so as to sink in fresh water to a 

 point near the top of the stem. The stem is graduated to read between 

 1.000 and 1.031, the figures representing the specific gravity; that is, 

 they show the weight of the salt water, an equal body of fresh water 

 being supposed to weigh 1.000. 



In practice a scale having the entire range would be too long for 

 safety and convenience, and therefore the salinometers are made in 

 sets of three, reading from 1.000 to 1.011, from 1.010 to 1.021, and from 

 1.020 to 1.031, respectively. 



There is also provided with them a deep copper cup or cylinder, 

 at one side of which a thermometer is attached (plate ii). The method 

 of using the salinometer is as follows: The cup is filled with the water 

 to be tested, the appropriate float is placed in the water, the density of 



