00 GENERAL MANAGEMENT OF 



extremely common. I have also put in a dozen or two of 

 the curious little fresh-water shrimp, Ascttus communis, 



which is extremely common in some of our streams. They 

 make excellent scavengers and are lively little creatures 

 besides, but do not live long in confinement, either bciti"- 

 eaten by the fish or otherwise disappearing. 



Sometimes you will perceive that your fish come fre- 

 quently to the surface to breathe or remain there. When 

 this happens, we may be certain that something is wrong 

 in the economy of the collection. This often indicates that 

 the inhabitants arc not supplied with enough oxygen for 

 support, and may be caused, first, by crowding the fish, 

 when some of them must be removed to another vessel, or 

 the water must be aerated; and to effect this, I have used 

 a contrivance which I will describe in chapter fourteen. 

 Secondly, it may result from there not being enough vege- 

 tation in the tank ; and this is a point that can only be 

 arrived at by direct experiment. Some writers will tell 

 you that one plant is sufficient for two fish, but they do 

 not say how large the plant is to be. But the fact of 

 the fish coming to the surface may be caused by some 

 decaying matter in the tank, either animal or vegetable, 

 that renders the water foul and unfit for the inhabitancc 

 of animals and must be at once removed. 



It should be remembered, when it is found necessary to 

 aerate the water, that we do not possess an Aquarium : 

 which is a collection of plants and animals that is self-support- 

 ing, self-renovating — that requires only the feeding of the 

 inhabitants and the watching for accidents. 



The temperature at which the water in the Aquarium 



