The great mistake made by most beginners in stocking an aquarium is in getting too much animal life in proportion to the cubic capacity of the tank. It is not often that we see too many plants, but we often see too many fishes. Fish are so easily obtained, they look so pretty, and form such interesting pets, that few beginners can refrain from keeping all that they can crowd in. Since the aquarium should be a means of instruction as well as pleasure, we would advise our readers to restrict themselves to one of each kind, unless in such cases as the sticklebacks, where pairs are necessary to enable us to watch their nest-building, hatching, and caring for their young.
Having obtained a tank and fitted it up with rock-work, and a nice clean floor, the first thing to be done is to set out those plants that are to take root in the subsoil. Then fill the tank gently and slowly with water, so as not to disturb the sand or gravel. This may be done by pouring the water on a large bung or piece of wood, which is allowed to float and rise as the tank fills, and is removed when sufficient water has been introduced. Floating plants may now be introduced, and also a few mollusks and tadpoles, and the whole allowed to stand for a few days exposed to the light, until the water has been brought into proper condition to receive the fishes and crustaceans. The latter may then be introduced. In all this, seek to obtain as great variety as possible, - unless, indeed, you desire to study carefully some one species or genus of plants or animals, and then, of course, you will be guided by the special purpose you may have in view. The inhabitants of the aquarium maybe rudely classed as follows: Plants, mollusks, insects, crustaceans, reptiles, and fishes. To each of these divisions we shall devote a few words, though from want of space we are unable to give anything like a description of the different species. To do this would require a large volume.