28 PRINCIPLES OF THE AQUARIUM. 



mutual compensation. The next important thing is 

 to know how many animals we can place in a tank 

 where there is already a certain number of plants. 

 Unfortunately, people who commence keeping aquaria 

 are usually too anxious to have as many and as 

 varied a stock of animals as possible, and most of 

 the evil which overtakes their endeavour arises from 

 such over-stocking. It is evident that if there are 

 more animals in the aquarium than there are plants 

 to provide oxygen for, all of them will have to go 

 short. This means universal sickness, and that 

 pitiful gasping for air which is often to be seen in 

 over-stocked aquaria. Before long it ends in death. 

 Perhaps one or two of the weaklier die first. Their 

 bodies lie on the bottom and are not removed. De- 

 composition sets in, and the water becomes fouler 

 than ever. A white fungus or rather the first stage of 

 growth in many microscopic fungi covers the bodies 

 of the survivors. The aquarium becomes a painful 

 scene of misery, disease, and death a too vivid 

 picture of similar conditions among humanity when 

 the latter is horded in fetid and over-populated 

 alleys, short of air, short of food, short of fresh, pure 

 water! What wonder that many an enthusiastic 

 young naturalist has been so thoroughly depressed 

 by his first mistake terminating so fatally, that he has 

 cast away the contents of his first aquarium, and 

 never tried afterwards ! 



And yet all this evil has been wrought for want of a 



