The Inhabitants of the Aquarium 113 



most globular in others. All, regardless of 

 shape and color, are suitable for the aqua- 

 rium. For some time after hatching the 

 young fish have a yellowish brown color, 

 which, in some cases, begins to change after 

 two or three months; others keep this color 

 for a considerable length of time ; cases have 

 been observed in which the change has not 

 taken place until after one or even two years, 

 while some specimens have kept their orig- 

 inal color altogether, showing thereby a ten- 

 dency to return to the character of the carp 

 ancestor. Those which do not change color 

 are often sold as so-called silver fish. One 

 of the peculiarities of the different varieties 

 of gold fish is that the older fishes change 

 their color altogether from gold to silver, or 

 vice versa, or develop markings of the dif- 

 ferent colors enumerated before. It is not 

 satisfactorily explained, by what these 

 changes, which in no way influence the 

 health of the fishes, are caused. Different 

 explanations, such as change of water, cli- 



