52 NEW YORK AQUARIUM NATURE SERIES 



may be taken for granted that something is wrong, and a careful 

 study should be made to ascertain the exact nature of the diffi- 

 culty. 



The most frequent cause of trouble for the beginner is lack 

 of oxygen. The symptoms are rapid or labored breathing or the 

 fishes remain at the surface and often take air-bubbles into their 

 mouths. On adding fresh water they should become normal in a 

 little while. Before changing the water in a balanced aquarium 

 it may be better to try aerating by dipping it up and pouring it 

 back in a slender stream from the height of a foot or so. By this 

 means small air bubbles will be carried under, and within a few 

 minutes the oxygen in the water will be renewed. It must be 

 remembered that insufficient oxygen means partial suffocation 

 and therefore continual distress to the fishes until a satisfactory 

 condition of aeration is established. 



On dark days, when the plants are not giving off much oxy- 

 gen, or if the temperature is too high, so that the water does not 

 so readily retain the oxygen, the fishes may remain at the sur- 

 face. If they insist on doing this in bright weather with the 

 temperature of the water not above 65 or 70 degrees there is 

 something wrong with the balance which should be remedied at 

 once before the fishes are weakened and rendered subject to 

 disease. It may result from decomposition of unconsumed food 

 or of a dead snail, and cleaning should be resorted to at once. If 

 the condition comes on gradually, it is probably caused by lack of 

 plant growth. At any rate, the balance is disturbed and must be 

 restored before graver difficulties follow. 



Of organic diseases in fishes we know very little, except that 

 such do exist. The most common troubles affecting aquarium 

 fishes are due to improper feeding. The first result is, of course, 

 mtestinal trouble, either diarrhoea or constipation. The latter is 

 more easily diagnosed, as the evidences are a distended or 

 bloated condition of the abdomen, coupled with difficulty in void- 

 ing excrement. Over-feeding and improper foods are the main 

 causes. In any case the diet should be cut down — starvation for 

 a few days will not hurt the fishes in the least— and afterwards 

 they should be fed sparingly on prepared fish-food until the 

 symptoms are no longer observed. 



Another disease marked by a bloated appearance is that 

 known as dropsy. In this case other parts than the abdomen are 

 affected, and the distension of the skin causes the scales to stand 



