Sididae and Daphniidae 219 



Peak cultures seem to require from 30 to 50% more cotton seed meal 

 than soy bean meal and the culture period is somewhat longer than with 

 the former. On the other hand, cotton seed meal, like animal manures, 

 stains the water a deep brown, resulting in deeply colored red Daphnia. 

 The deep color seems also to prevent undue growth of blanket algae. The 

 soy bean meal produces light gray Daphnia and an abundance of free- 

 moving micro-algae which color the water green. It also encourages the 

 growth of blanket algae. 



The quantity of Daphnia necessary to start a successful culture, within 

 certain limits, is not so important as the physiological condition of the 

 mother organisms. They should be active summer egg producers. Al- 

 most always a few will be found with winter eggs. If the proportion is 

 large, specimens from such a culture should be discarded. In the ex- 

 periments reported here, from 25 to 100 cc. of mother organisms were 

 generally used. We believe that 50 cc. is sufficient for 100 cu. ft. of water. 

 They are measured by pouring water containing Daphnia into a tall 

 graduate held in the sunlight. The individuals very soon settle to the 

 bottom and the quantity may be determined with ease. 



The water supply of the seven concrete propagating ponds used is con- 

 trolled by dams in such a way that a constant level is automatically 

 maintained in each pond without overflow. The water is therefore stag- 

 nant at all times. Each pond has an independent drain which leads 

 directly into a bass-rearing pond. Hence all food organisms produced 

 may be drained off directly into the rearing pond by removing a stand- 

 pipe. During the last four years it has been customary to operate them 

 in rotation, thus producing several crops in each during the summer 

 season. 



M. E. D. 



DAPHNIA CULTURE 



Libbie H. Hyman, New York City 



TO CULTIVATE Daphnia, bring lettuce leaves, preferably of a green, 

 leafy type of lettuce such as Boston lettuce, to a boil. Do not 

 continue boiling. Place the boiled lettuce leaves in containers having 

 6 to 8 inches of water in the proportions of 1 good-sizsd lettuce leaf to 

 each 6 square inches of bottom. After 2 or 3 days add Daphnia. These 

 may be obtained often from pet shops or dealers in biological supplies 

 and also in almost any somewhat stagnant pond by means of a plankton 

 net. After the lettuce leaves have disintegrated additional lettuce leaves 

 should be added from time to time and also small pieces of raw liver or 

 the entrails or corpses of small animals such as tadpoles, mice, rats, etc . 

 In adding such material it is essential that only a moderate quantity be 

 used. The water must not become foul or cloudy as this will kill the 



