"The floor is of sand like the mountain drift,
And the pearl-shells spangle the flinty snow;
From the coral rocks the sea-plants lift
Their boughs, where the tides and billows flow.
* * * * *
"And life in rare and beautiful forms
Is sporting amid those bowers of stone,
And is safe, when the wrathful spirit of storms
Has made the top of the waves his own."[C]
[Footnote C: Percival.]
Upon the bottom, at various depths, lies that brilliant Radiate—type of his class—the Star-fish. These are quiet and harmless creatures, and favorites in the aquarium, from the pretty contrast they make with marine plants and other objects.
The perfect transparency, elegant form, and graceful navigation of the Medusae, or Jelly-fishes, render them much admired in their native haunts, and prized for the aquarium. But they are very delicate. How beautiful and remarkable are these headless Discophori, as they float, and propel themselves with involutions of their disks and gently trailing tentacles, and the central peduncle hanging far below, like the clapper of a transparent bell! And yet these wonders are but so much sea-water, inclosed in so slight a tissue that it withers in the sun, and leaves only a minute spot of dried-up gelatinous substance behind.
Finally come the Fishes, many of which are of similar genera to those recommended for the fresh-water tank. The Black Goby is familiar, tamable, but voracious; the Gray Mullet is very hardy, but also rather savage; the Wrasses are some of the most showy fish,—called in some parts of the country Cunners,—and of these, the Ancient Wrasse, (Labrus maculatus,) covered with a network of vermilion meshes on a brown and white ground, is the most elegant.
Some points of general management are so important, and some dangers so imminent, that we cannot pass them by unnoticed. The aquarian enthusiast is very apt to be in too great haste to see everything going on, and commits the common error of trying too many things at once. The aquarium must be built up slowly and tentatively, object by object: plants first, and of the simplest kinds; and not until they are well settled, and the water beaded with oxygen bubbles, should we think of introducing living creatures,—and even then only the hardier kinds of actinias, mollusks, and crabs. All delicate animals must be intrusted one by one to their new home, and carefully watched for deaths and decay, which, whether arising from dead plants or animals, ruin everything very quickly, unless they be promptly removed. For sulphuretted hydrogen, even in very minute quantities, is sure death to all these little creatures.
The emanations from paint and putty are often fatal in new tanks. Several weeks' exposure to water, air, and sunlight is necessary to season the new-made aquarium. Of equal consequence is it that the water be absolutely pure; and if brought from the sea, care must be exercised about the vessel containing it. Salt acts upon the glazing of earthen ware of some kinds. Stone or glass jars are safest. New oak casks are fatal from the tannin which soaks out; fir casks are safe and good. So delicate and sensitive are the minute creatures which people the sea, that they have been found dead on opening a cask in which a new oak bung was the only source of poison. And no wonder; for a very slight proportion of tannic acid in the water corrugates and stiffens the thin, smooth skin of the anemone, like the tanning of leather.
A certain natural density of the sea-water must also be preserved, ranging between no wider limits than 1026 and 1028. And in the open tank evaporation is constantly deranging this, and must be met by a supply from without. As the pure water alone evaporates, and the salts and earthy or mineral constituents are left behind, two things result: the water remaining becomes constantly more dense; and this can be remedied only by pure fresh water poured in to restore the equilibrium. Hence the marine aquarium must be replenished with fresh water, until the proper specific gravity, as indicated by the hydrometer, is restored.