TROPICAL AQUARIUM FISHES 135 
get rid of them it is necessary to boil or renew the sand or else keep other 
fishes in the aquarium for a long time. The worms have to be eaten off 
many times before the stock dies. Germicides strong enough to kill them 
will also destroy the plants, as they can withdraw into the sand. Along 
the edges of ditches they are often so numerous as to make a solid rusty 
red color. If they are scraped up together with the dirt and then washed 
free they are greatly enjoyed by small tropical fishes. 
Fairy Shrimp (Gammarus). While freshwater shrimp is not plenti- 
ful enough anywhere to feed in large quantities, it is a delicate morsel for 
grown fishes and should be taken as opportunity offers. They are found 
principally in small streams, under stones and around decaying wood. 
Placed in a large aquarium or tank with plenty of vegetation they will 
multiply rapidly. 
Fic. 91. Farry Surimp (Enlarged 3 times) 
Fic. 92. Water-AseL (Enlarged 3 times) 
Water-Asel (Asellopus) is found in still or slowly moving water, 
usually in the mud or clinging to vegetation. It cannot move rapidly 
like Fairy Shrimp, but both are enemies of very small fry and both are 
greedily taken as food by larger aquarium fishes, although the shrimp 
move so rapidly that highly developed fishes have trouble in catching 
them. erge 
Fic. 93 Fic. 94 : 
Asplanchnopus myrmelco Pterodina patina Noteus quadracornis 
Taree TypicaL Rotiriers (Greatly magnified) 
Infusoria and Rotifera. Of prime importance as food for very small 
fishes are the Infusoria and other microscopic creatures of still water. 
Some idea of their minuteness may be had when it is pointed out that 
they are the natural food of Daphnia, Cyclops and other small crustaceans. 
All except the very largest of the infusorians will pass through ordinary 
cheesecloth nets, but silk bolting-cloth of fine texture will hold those 
