In selecting plants for the aquarium some regard is to be paid to the amount of oxygen they will evolve, and to their hardiness, as well as to their beauty. When it is desired to introduce the fishes without waiting long for the plants to get settled and to have given off a good supply of oxygen, there is no plant more useful than the Callitricke, or Brook Star-wort. It is necessary to get a good supply, and pick off the green heads, with four or six inches only of stem; wash them clean, and throw them into the tank, without planting. They spread over the surface, forming a rich green ceiling, grow freely, and last for months. They are continually throwing out new roots and shoots, and create abundance of oxygen. Whenever desired, they can be got rid of by simply lifting them out.
The Vallisneria, or Tape-Grass, common in all our ponds, is essential to every fresh-water tank. It must be grown as a bottom-plant, and flourishes only when rooted. The Nitella is another pleasing variety. The Ranunculus aquatilis, or Water-Crowfoot, is to be found in almost every pond in bloom by the middle of May, and continues so into the autumn. It is of the buttercup family, and may be known as a white buttercup with a yellow centre. The floating leaves are fleshy; the lower ones finely cut. It must be very carefully washed, and planted from a good joint, allowing length enough of stem to reach the surface. Some of the blossom-heads may also be sprinkled over the surface, where they will live and bloom all through the summer. The Hydrocharis, or Frog's-Bit, and the Alisma, or Water-Plantain, are also easily obtained, hardy and useful, as well as pleasing. Many rarer and more showy varieties may be cultivated; we have given only the most common and essential. All the varieties of Chara are interesting to the microscopist, as showing the phenomenon of the circulation of the sap, or Cyclosis.
Of the living tenants of the aquarium, those most interesting, as well as of the highest organization, are the fishes. And among fishes, the family of the Cyprinidae are the best adapted to our purpose; for we must select those which are both hardy and tamable. Cyprinus gibelio, the Prussian Carp, is one of the best. It will survive, even if the water should accidentally become almost exhausted of oxygen. It may be taught, also, to feed from the hand. None of the carp are very carnivorous. Cyprinus auratus, or the Gold-fish, is one of the most ornamental objects in an aquarium. But the Minnow, C. phoxinus, is the jolliest little fish in the tank. He is the life of the collection, and will survive the severest trials of heat and cold. The Chub, a common tenant of our ponds, is also a good subject for domestication. The Tench and Loach are very interesting, but also very delicate. Among the spiny-finned fishes, the Sticklebacks are the prettiest, but so savage that they often occasion much mischief. For a vessel containing twelve gallons the following selection of live stock is among those recommended: Three Gold Carp, three Prussian Carp, two Perch, four large Loach, a dozen Minnows, six Bleak, and two dozen Planorbis. Some varieties of the Water-Beetles, or Water-Spiders, which the fishes do not eat, may also well be added. The Newt, too, is attractive and harmless.
All may go on well, and the water remain clear; but after the tank has been established several weeks, the inner sides of the glass will show a green tinge, which soon increases and interferes with the view. This is owing to the growth of a minute confervoid vegetation, which must be kept down. For this purpose the Snail is the natural remedy, being the ready scavenger of all such nuisances. Snails cling to the sides, and clean away and consume all this vegetable growth. The Lymnea is among the most efficient, but unfortunately is destructive, by eating holes in the young fronds of the larger plants, and thus injuring their appearance. To this objection some other varieties of snail are not open. The Paludina and Planorbis are the only kinds which are trustworthy. The former is a handsome snail, with a bronze-tinted, globular shell; the latter has a spiral form. These will readily reduce the vegetation. And to preserve the crystal clearness of the water, some Mussels may be allowed to burrow in the sand, where they will perform the office of animated filters. They strain off matters held in suspension in the water, by means of their siphons and ciliated gills. With these precautions, a well-balanced tank will long retain all the pristine purity of Nature.
Specimens for the river aquarium may be readily obtained in almost any brook or pool, by means of the hand-net or dredge. It will be astonishing to see the variety of objects brought up by a successful haul. Small fish, newts, tadpoles, mollusks, water-beetles, worms, spiders, and spawn of all kinds will be visible to the naked eye; while the microscope will bring out thousands more of the most beautiful objects.
A very different style of appearance and of objects distinguishes the
Salt-water or Marine Aquarium.
As the greater part of the most curious live stock of the salt-water aquarium live upon or near the bottom, so the marine tank should be more shallow, and allow an uninterrupted view from above. Marine creatures are more delicately constituted than fresh-water ones; and they demand more care, patience, and oversight to render the marine aquarium successful.
Sea-sand and pebbles, washed clean, form the best bottom for the salt-water aquarium. It must be recollected that many of the marine tenants are burrowers, and require a bottom adapted to their habits. Some rock-work is considered essential to afford a grateful shelter and concealment to such creatures as are timid by nature, and require a spot in which to hide: this is true of many fishes. Branches of coral, bedded in cement, may be introduced, and form beautiful and natural objects, on which plants will climb and droop gracefully.
Sea-water dipped from the open sea, away from the mouths of rivers, is, of course, the best for the marine aquarium. If pure, it will bear transportation and loss of time before being put into the tank. It may, however, not always be possible to get sea-water, particularly for the aquarium remote from the seaboard, and it is therefore fortunate that artificial sea-water will answer every purpose.
The composition of natural sea-water is, in a thousand parts, approximately, as follows: Water, 964 parts; Common Salt, 27; Chloride of Magnesium, 3.6; Chloride of Potassium, 0.7; Sulphate of Magnesia, (Epsom Salts,) 2; Sulphate of Lime, 1.4; Bromide of Magnesium, Carbonate of Lime, etc., .02 to .03 parts. Now the Bromide of Magnesium, and Sulphate and Carbonate of Lime, occur in such small quantities, that they can be safely omitted in making artificial seawater; and besides, river and spring water always contain a considerable proportion of lime. Therefore, according to Mr. Gosse, we may use the following formula: In every hundred parts of the solid ingredients, Common Salt, 81 parts; Epsom Salts, 7 parts; Chloride of Magnesium, 10 parts; Chloride of Potassium, 2 parts; and of Water about 2900 parts, although this must be accurately determined by the specific gravity. The mixture had better be allowed to stand several days before filling the tank; for thus the impurities of the chemicals will settle, and the clear liquor can be decanted off. The specific gravity should then be tested with the hydrometer, and may safely range from 1026 to 1028,—fresh water being 1000. If a quart or two of real sea-water can be obtained, it is a very useful addition to the mixture. It may now be introduced into the tank through a filter. But no living creatures must be introduced until the artificial water has been softened and prepared by the growth of the marine plants in it for several weeks. Thus, too, it will be oxygenated, and ready for the oxygen-using tenants.