It is a singular fact, that water which has been thus prepared, with only four ingredients, will, after being a month or more in the aquarium, acquire the other constituents which are normally present in minute quantities in the natural sea-water. It must derive them from the action of the plants or animals, or both. Bromine may come from sponges, or sea-wrack, perhaps. Thus artificial water eventually rights itself.
The tank, having been prepared and seasoned with the same precaution used for the river aquarium, and having a clear bottom and a supply of good water, is now ready for planting. Many beautifully colored and delicately fringed Algae and Sea-Wracks will be found on the rocks at low tide, and will sadly tempt the enthusiast to consign their delicate hues to the aquarium. All such temptations must be resisted. Green is the only color well adapted for healthy and oxygenating growth in the new tank. A small selection of the purple or red varieties may perhaps be introduced and successfully cultivated at a later day, but they are very delicate; while the olives and browns are pretty sure to die and corrupt the water. It must be remembered, too, that the Algae are cryptogamous, and bear no visible flowers to delight the eye or fancy. Of all marine plants, the Ulva latissima, or Sea-Lettuce, is first and best. It has broad, light-green fronds, and is hardy and a rapid grower, and hence a good giver of oxygen. Next to this in looks and usefulness comes the Enteromorpha compressa, a delicate, grass-like Alga. After a while the Chondrus crispus, or common Carrageen Moss, may be chosen and added. These ought to be enough for some months, as it is not safe to add too many at once. Then the green weeds Codium tomentosum and Cladophora may be tried; and, still later, the beautiful Bryopsis plumosa. But it is much better to be content with a few Ulvae, and others of that class, to begin with; for a half dozen of these will support quite a variety of animal life.
After a few hardy plants are well set, and thriving for a week or two, and the water is clear and bubbly with oxygen, it will be time to look about for the live stock of the marine aquarium. Fishes, though most attractive, must be put in last; for as they are of the highest vitality, so they require the most oxygen and food, and hence should not be trusted until everything in the tank is well a-going.
The first tenants should be the hardy varieties of the Sea-Anemones, or Actiniae,—which are Polyps, of the class Radiata. The Actinia mesembryanthemum is the common smooth anemone, abounding on the coast, and often to be found attached to stones on the beach. "When closed," says Mr. Hibbert, "it has much resemblance to a ripe strawberry, being of a deep chocolate color, dotted with small yellow spots. When expanded, a circle of bright blue beads or tubercles is seen within the central opening; and a number of coral-like fingers or tentacles unfold from the centre, and spread out on all sides." It remains expanded for many days together, if the water be kept pure; and, having little desire for locomotion, stays, generally, about where it is placed. It is a carnivorous creature, and seeks its food with its ever-searching tentacles, thus drawing in fishes and mollusks, but, most frequently, the minute Infusoria. Like other polyps, it may be cut in two, and each part becomes a new creature. It is a very pretty and hardy object in the aquarium. There are many varieties, some of which are very delicate, as the Actinia anguicoma, or Snaky-locked Anemone, and the pink and brown Actinia bellis, which so resembles a daisy. Others, as the Actinia parasitica, are obtainable only by deep-sea dredging; "and, as its name implies, it usually inhabits the shell of some defunct mollusk. And more curious still, in the same shell we usually find a pretty crab, who acts as porter to the anemone. He drags the shell about with him like a palanquin, on which sits enthroned a very bloated, but gayly-dressed potentate, destitute of power to move it for himself."[B]
[Footnote B: Hibbert's Book of the Aquarium.]
The Actinia gemmacea, or Gemmed Anemone, the Actinia crassicornis, and the Plumose Anemone are all beautiful, but tender varieties.
The Anemones require but little care; they do not generally need feeding, though the Daisy and Plumose Anemone greedily take minced mutton, or oyster. But, as a rule, there are enough Infusoria for their subsistence; and it is safer not to feed them, as any fragments not consumed will decay, and contaminate the water.
Next in order of usefulness, hardiness, and adaptability to the new aquarium, come the Mollusks. And of these, Snails and Periwinkles claim our respectful attention, as the most faithful, patient, and necessary scavengers of the confervoid growths, which soon obscure the marine aquarium.
"It is interesting," says Mr. Gosse, "to watch the business-like way in which the Periwinkle feeds. At very regular intervals, the proboscis, a tube with thick fleshy walls, is rapidly turned inside out to a certain extent, until a surface is brought into contact with the glass having a silky lustre; this is the tongue; it is moved with a short sweep, and then the tubular proboscis infolds its walls again, the tongue disappearing, and every filament of Conferva being carried up into the interior, from the little area which had been swept. The next instant, the foot meanwhile having made a small advance, the proboscis unfolds again, the makes another sweep, and again the whole is withdrawn; and this proceeds with great regularity. I can compare the action to nothing so well as to the manner in which the tongue of an ox licks up the grass of the field, or to the action of the mower cutting swath after swath."
Of Crustacea, the Prawns and the smaller kinds of Crabs may be admitted to the aquarium, though but sparingly. They are rude, noisy, quarrelsome, and somewhat destructive,—but, for the same reason, amusing tenants of the tank.