TROPICAL AQUARIUM FISHES 131 



would sink to the bottom, as they are heavier than water and have no 

 air bladder. A greatly magnified illustration is shown in Fig. 83. 



Daphnia (incorrectly pronounced "dafifney") are known among fish 

 breeders as "insects," but they are really not such, being perfect fresh- 

 water crustaceans as much as a crayfish. The shell though soft contains 

 mineral elements which are very desirable, while the flesh itself is easily 

 digested and nutritious. This little creature is found nearly all over the 

 world, principally in still pools where there are no fish. For the practical 

 purpose of catching daphnia in sufficient quantities to feed fish the 

 collector should hunt pools in which there is considerable animal or vege- 

 table decomposition in process. This decomposition favors the growth 

 of infusoria, small members of the animal kingdom on which daphnia 

 feed. Such conditions are found to perfection in the pools on the 

 grounds where city refuse is dumped. When the conditions are favor- 

 able the daphnia rise to the surface in such quantities as to color the 

 water, the usual color being a rusty red. The color varies from this to 

 olive and gray. Fish breeders like to see the daphnia as bright a red as 

 possible, although it is an open question as to whether the red ones are 

 better food. The same individuals will alternate in color, probably due 

 to a difference in food. Usually these crustaceans are not so plentiful 

 as to color the water and we have to use our eyes more closely to locate 

 them. The collector should provide himself with a cheesecloth net about 

 12 inches in diameter and 15 inches deep, fastened on a pole or jointed 

 handle not less than 6 feet long. If an examination of the water does 

 not at first reveal any daphnia, the net should be tried anyhow, using a 

 gentle stirring motion back and forth, to stir up the bottom water. 

 Daphnia have very peculiar habits and one can never tell from day to 

 day just how they are to be found, so that the collector will always have 

 to depend somewhat on his own resources. If an examination of the net 

 after dipping for a few minutes shows nothing, try elsewhere. If a 

 colony has been located do not take too many into the net at one time, 

 as the weight of the top ones crushes those beneath. A mass that would 

 bulk about equivalent to an orange should not be exceeded. Reverse 

 the net into carrying pail and repeat until the water is thick with daphnia. 

 In cool weather the pail may be carried in this crowded condition for 

 about an hour. If the day is hot, a piece of ice should be added to the 

 water — enough to keep temperature down until home is reached. News- 

 paper wrapped about the can helps the ice melt more slowly. As soon 

 as home is reached, add fresh water to the pail and transfer the daphnia 

 to tubs or tanks kept for the purpose. Like fish, the water they are in 

 should have as much air surface as possible. Do not try to keep too 

 many in stock, as overcrowding suffocates a number and these in turn 

 decomposing kill the living ones. The cooler they are kept, the longer 



