As a domestic ornament, combining instruction with a novel kind of recreation, the fresh-water aquarium has already taken precedence of the marine, and will doubtless keep it. The marine tank is certainly the most attractive to the eyes of a student, but the fresh-water tank is at once cheaper, more easily stocked and managed, and unattended with the risks that beset marine life even under the most favourable circumstances. The nearest brook or pond will furnish fluviatile specimens, and generally speaking, these are so easy of management, that a child might set up a tank of this kind, and maintain it in a flourishing condition.
Yet it must not be supposed that there is nothing to learn even in this case, though the experience acquired through many trials and disappointments may be very briefly told for the benefit of beginners. As a rule, it may be held that either rockwork or branching coral is a necessity, as well as an ornament of a marine tank, but rockwork of any kind is a positive injury to a fresh-water collection; it soon gets covered with confervae, which is the greatest enemy to the collection. It may here be mentioned, too, that propagating glasses are not strong enough to bear the weight of rockwork ; and if they were, it is scarcely an ornament to any cylindrical vessel: so that in the case of marine stock, a piece of branching coral is the only ornament of the kind suited to a cylinder.
In forming the bed of the fresh-water tank, we should advise the use of sharp sand only with a few small pebbles, the whole well washed previously. Writers on aquarian subjects have invariably recommended the use of mould, but the tank can be kept more free from objectionable vegetable growths, and hence more brilliantly transparent, if pure sand be used, while all the ordinary weeds, Vallisneria. Anacharsis, lilies, 4c, grow just as well in sand as in mould, and if the barbel and stone loach are inclined to stir it up with their bearded snouts, there is no muddy deposit on the sides of the vessel in consequence. Indeed, when a hungry loach smells a worm, he will stir up the bottom as violently as a cook would stir up batter; and if there be any solvent matter there, the leaves of the Vallisneria and Stratoides will soon be coated with slime, and upon that slime fucus will soon appear.
As to the plants for a fresh-water tank, there is scarcely a weed to be found in any brook or river but may be safely transplanted to it, a little washing and trimming being necessary to remove decaying matter. J lisneria spiralis is essential, for it is one of the best oxygen makers, a free grower, and very elegant in outline; the great water soldier (Stratoides) with its spiny leaven shaped like those of the Yucca gloriosa. and with its elegant offshoots starting up like so many umbrella frames on very long stems, is another good oxygen maker. The new water-weed Anacharsis alsinastrum, the pretty Ranunculus aquatalis, Myriophyl-um spicatum and Potamogeton of any species, besides the smaller kinds of water lily, flourish amazingly, and give the tank a fresh and luxuriant appearance. To those who live in the north, we commend a little plant which may be found on the shallow margins and lakes at great elevations. It is the pretty awl-wort, Subularia aqualica, a member of the extensive family of Cruciferae. It produces numerous rush-like leaves, each of them Curved at the point like a cobbler's awl - whence its name ; and in July sends up a little head of tetraform white blossoms strongly resembling those of the watercress. Though somewhat rare, it takes to its indoor home kindly, and blooms freely beneath, the surface, very much to the astonishment of non-botanical observers.
Unlike the marine tank, the fresh-water vessel may be stocked with fishes and plants at the same time, but the precaution must be taken to throw in a few handfuls of some common weed, which should be left to float about and supply oxygen until the plants at the bottom have fairly taken root. A mass of floating weeds is a decided improvement to the tank, and creates a rich green shadow in which the fishes delight, and most of the succulent weeds from brooks will flourish in this way for many months, and even increase considerably by the numerous white rootlets they send down from their joints, some of which will probably reach the bottom and produce a forest of vegetation.
Among the animal stock, minnows, carp, barbel, stone loach, perch, dace, roach, bream, bleak, and chub, and water lizards, are all suitable. Dace and roach are perhaps the most delicate; carp and minnows the most hardy. We have at the present time about a hundred of various kinds of fresh-water fish, some of them so tame as to take food from the hand, and even nibble the fingers sharply; they swarm to the side of the vessel when we tap on it with the finger rails, and will hunt a piece of bread or white of egg, as we move it up and down outside, in a lively style that would make phlegmatic dulness laugh itself into hysterics anytime. The molluscs to be most strongly recommended are Planorbis corneus, a handsome snail of a ram's-horn shape, Paludina Vivipara, all the kinds of Lymnea, Bithinia tentacula, and the very useful bivalves, the swan mussel, Anoden cygneus, and the duck mussel, Unis pic-torum. Though we recommend these, we are bound to add that the Lymnea, though good cleaners, are given to the vice of eating the Vallisneria and the Stratoides; that Paludina is of little use as a cleaner, his beauty only recommending him ; and that Planorbis is the best of all cleaners, and rarely deserts the side of the vessel, where snails should remain as much as possible.
We seldom feed our marine stock, but occasionally the flesh of a cooked prawn, or a few minute shreds of mutton, may be given ; fresh-water stock delight in the crumbs of home-baked bread, white of egg minced very tine, soft insect food of any kind, particularly maggots and flies, and, above all, small red worms. A romp may be got up at any time, by dropping in a lively worm;
The minnows seize it and fight till they tear it in half; before they can gorge it, the loach attack them, and there is so much floundering, that the fragments of the worm are dropped into the jaws of a newt, who seizes it in the manner of a cat seizing a mouse, and the game ends by the newt retaining a firm hold, with half the worm projecting from his mouth, and half a dozen fishes scrambling to tear it out, till the newt triumphs by a sullen perseverance, and gets the prey fairly swallowed, in little less than an hour, during the whole of which time it is worried, in vain, by almost every one of its more lively neighbours.
In every case the success of an Aquarium depends upon the adjustment of a fair balance of forces, and if care be taken to remove any matter that might decay and create corruption, and to introduce only as much animal life as the plants are capable of supplying with oxygen, death will then be a rare event. The water should not be changed at all, that is one of the leading features of the Aquarium; and if [you cannot keep your stock in health, without a change of water, depend upon it you have gone the wrong way to work, and must begin again de novo. An important matter is to avoid overstocking; keep down the amount of animal life, until the plants are strong, and then increase it slowly, so as to see your progress safely. Whenever you find your fishes gasping at the surface, ho sure that there is insufficiency of oxygen, and remove a few to another vessel; for whenever a fish stands upon his tail at the surface for any length of time, it is certain that disease is at work, and that his hours are numbered.