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 “daffney”) 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 
