326 THE AQUARIUM 



Some aquatic insects, such as the Water-strider and 

 Whirligig Beetle, may safely be kept in the aquarium, but 

 it is best to avoid the larger and stronger species, many 

 of which will attack and kill the fishes. Dragon-fly and 

 other larvae must not be introduced, as they are among the 

 most destructive enemies of young or small fishes. 



Turtles and crayfish are interesting and will thrive if 

 properly treated, but must not be kept in the general 

 aquarium. Even the smallest specimens will attack the 

 fishes, killing the weaker ones and tearing the tails of those 

 strong or active enough to escape them. 



Diseases 



Unfortunately, in common with other captive creatures, 

 as well as those in freedom, fishes are subject to a variety 

 of diseases. These are not numerous, and the most com- 

 mon are caused by fungi or animal parasites. If proper 

 care is used in the introduction of plants, attacks of this 

 nature are infrequent. When they do occur, the best course 

 to pursue is to remove and destroy the entire contents of the 

 infected tank, purify it thoroughly and restock it. 



If fishes are carelessly handled scales will be loosened or 

 removed, rendering the specimen subject to attack by 

 fungus, the spores of which are ever present in the water. 

 The result is the appearance of a milky, stringy cloud 

 which adheres to the victim and moves about with it. When 

 this is noticed the fish should be removed, and immersed for 

 a short time in a weak solution of salt in water. After this 

 treatment has been repeated two or three times, improve- 

 ment will be noted, and a full recovery may finally be 

 achieved, but once the fungus has penetrated beneath the 

 scales it is difficult to eradicate. 



The so-called black fungus is a common disease among 



