478 



BULLETIN OF THE BUREAU OP FISHERIES 



The average of the "successful" years shows that the total quantity filtered by one 

 oyster during this time was 203 liters more than the amount filtered at normal 

 temperatures, while the average of the "failure" years was 159 liters less than the 

 normal amount. In the following table the average liters of water filtered monthly 

 and the total number of liters filtered during the successful and unsuccessful years 

 are given. 



Table 13. — Comparison of the quanliiy of water filtered by an average oyster during setting and non- 

 setting years in Long Island Sound 



, During the three years when air and water temperatures were above normal we 



! should expect to find a greater quantity of spawn in the oysters because of the direct 

 r influence of higher temperatures on the development of the gonads and because of the 

 |i| greater feeding activity on the part of the oysters. The time when oysters are found 

 f]l to be ripe also varies from year to year and can be correlated with previous water 

 I temperatures. The condition of the gonads observed in 1925, 1926, and 1927 support 

 these views and show that the development of the gonads was greater and time of 

 ripening earher when water temperatures were above normal, as in 1925, while the 

 opposite was true in the other two years, when temperatures below normal occurred. 



TIME OF SPAWNING 



4i The time when the ripe oyster discharges its spawn into the water depends largely 



upon temperature. Studies of oyster spawning in Milford Harbor, as well as those 

 of Galtsoff (unpublished manuscript, 1926), Churchill (1919), Nelson (1924), and 

 Outsell (1922), show that spawning seld om occurs when the water temperature _is 

 b glow 20° C . In many instances in 1925 and 1926 spawning was observed to take 

 place in tanks and floats at temperatures ranging from 20° to 27°^ C. The oysters 

 used in these experiments came from Milford Harbor and the offshore beds in Long 

 Island Sound. It was found that those from the Sound, where the water temperature 

 is much lower than in the harbor, spawned in about half an houj^aj; 2 0° to 22° C, 

 while the oysters from the warmer harbor waters required several hours' exposure 

 to this temperature before spawning occurred, ori^^_the other hand, tIiex_could be 

 i ndu ced^ to spawn in half^an ho ur by increasing the t emperature from ^3° to 27 ° C . 

 The time of spawning of the oyster on the beds was determined, first, by examina- 

 tion of the plankton samples for the presence of larvse 24 to 48 hours old and, second, 

 by observations as to the quantity of spawn in the o/sters. I n_ Connec ticut waters 

 there generalLyificcur two spawnings, the first being very Hght and occurring about 

 the middle of July, while the second is^heavier^an^occiirsjiboutjhej^t of August. 

 The time of spawning was found to vary somewhat from year to year in accordance 

 with water temperature and tidal conditions. The dates on which spawning occurred 



