The Atlantic Monthly, Volume 08, No. 47, September, 1861

The term vivarium was used among the ancients to signify many things,—from the dens of the wild animals which opened under the Colosseum, to an oyster-bed; and so now it may mean any collection of living creatures. Hence it could convey no distinct idea of a marine collection such as we propose to describe. The term aqua was added to express the watery element; but the compound aqua-vivarium was too clumsy for frequent employment, and the abbreviated word aquarium has come into general use.

Thus the real Aquarium is a water-garden and a menagerie combined,—and aims to show life beneath the waters, both animal and vegetable, in all the domestic security of its native home, and in all the beauty, harmony, and nice adaptation of Nature herself. It is no sudden discovery, but the growth of a long and patient research by naturalists.

"What happens, when we put half a dozen gold-fish into a globe? The fishes gulp in water and expel it at the gills. As it passes through the gills, whatever free oxygen the water contains is absorbed, and carbonic acid given off in its place; and in course of time, the free oxygen of the water is exhausted, the water becomes stale, and at last poisonous, from excess of carbonic acid. If the water is not changed, the fishes come to the surface and gulp atmospheric air. But though they naturally breathe air (oxygen) as we do, yet they are formed to extract it from the water; and when compelled to take air from the surface, the gills, or lungs, soon get inflamed, and death at last puts an end to their sufferings.

"Now, if a fish-globe be not overcrowded with fishes, we have only to throw in a goodly handful of some water-weed,—such as the Callitriche, for instance,—and a new set of chemical operations commences at once, and it becomes unnecessary to change the water. The reason of this is easily explained. Plants absorb oxygen as animals do; but they also absorb carbonic acid, and from the carbonic add thus absorbed they remove the pure carbon, and convert it into vegetable tissue, giving out the free oxygen either to the water or the air, as the case may be. Hence, in a vessel containing water-plants in a state of healthy growth, the plants exhale more oxygen than they absorb, and thus replace that which the fishes require for maintaining healthy respiration. Any one who will observe the plants in an aquarium, when the sun shines through the tank, will see the leaves studded with bright beads, some of them sending up continuous streams of minute bubbles. These beads and bubbles are pure oxygen, which the plants distil from the water itself, in order to obtain its hydrogen, and from carbonic acid, in order to obtain its carbon."45

Thus the water, if the due proportion of its animal and vegetable tenants be observed, need never be changed. This is the true Aquarium, which aims to imitate the balance of Nature. By this balance the whole organic world is kept living and healthy. For animals are dependent upon the vegetable kingdom not only for all their food, but also for the purification of the air, which they all breathe, either in the atmosphere or in the water. The divine simplicity of this stupendous scheme may well challenge our admiration. Each living thing, animal or plant, uses what the other rejects, and gives back to the air what the other needs. The balance must be perfect, or all life would expire, and vanish from the earth.

This is the balance which we imitate in the Aquarium. It is the whole law of life, the whole scheme of Nature, the whole equilibrium of our organic world, inclosed in a bottle.

For the rapid evolution of oxygen by plants the action of sunlight is required. That evolution becomes very feeble, or ceases entirely, in the darkness of the night. Some authorities assert even that carbonic acid is given off during the latter period. So, too, they claim that there are two distinct processes carried on by the leaves of plants,—namely, respiration and digestion: that the first is analogous to the same process in animals; and that by it oxygen is absorbed from, and carbonic acid returned to the atmosphere, though to a limited degree: and that digestion consists in the decomposition of carbonic acid by the green tissues of the leaves under the stimulus of the light, the fixation of solid carbon, and the evolution of pure oxygen. The theory of distinct respiration has been somewhat doubted by the highest botanical authority of this country; but the theory of digestion is indisputable. And it is no less certain that all forms of vegetation give to the air much more free oxygen than they take from it, and much less carbonic acid, as their carbonaceous composition shows. If fresh leaves are placed in a bell-glass containing air charged with seven or eight per cent. of carbonic acid, and exposed to the light of the sun, it will be found that a large proportion of the carbonic acid will have disappeared, and will be replaced by pure oxygen. But this change will not be effected in the dark, nor by any degree of artificial light. Under water the oxygen evolved from healthy vegetation can be readily collected as it rises, as has been repeatedly proved.

Why carbonic acid is, to a limited degree, given off by the plant in the night, is merely because the vital process, or the fixation of carbon and evolution of oxygen, ceases when the light is withdrawn. The plant is only in a passive state. Ordinary chemical forces resume their sway, and the oxygen of the air combines with the newly deposited carbon to reproduce a little carbonic acid. But this must be placed to the account of decomposing, not of growing vegetation; for by so much as plants grow, they decompose carbonic acid and give its oxygen to the air, or, in other words, purify the air.

It has been found by experiment, that every six pounds of carbon in existing plants has withdrawn twenty-two pounds of carbonic acid gas from the atmosphere, and replaced it with sixteen pounds of oxygen gas, occupying the same bulk. And when we consider the amount of carbon that is contained in the tissues of living, and of extinct vegetation also, in the form of peat and coal, we may have some idea of the vast body of oxygen which the vegetable kingdom has added to the atmosphere.

And it is also to be considered, that this is the only means we know of whereby free oxygen is given to supply the quantity constantly consumed in respiration, combustion, and other vast and endless oxygen-using processes. It follows, therefore, that animals are dependent upon plants for their pure oxygen, as well as for their food. But the vegetable kingdom might exist independently of the animal; since plants may derive enough carbon from the soil, enriched by the decaying members of their own race.

There is, however, one exception to the law that plants increase the amount of oxygen in the air. During flowering and fruiting, the stores of carbon laid up in the plant are used to support the process, and, combining with the oxygen of the air, both carbonic acid and heat are given off. This has been frequently proved. In large tropical plants, where an immense number of blossoms are crowded together, the temperature has risen twenty to fifty degrees above that of the surrounding air.

As most of the aquatic plants are cryptogamous, or producing by spores, and not by flowers, it seems probable that the evolution of carbonic acid and heat is much less in degree in them, and therefore less in the water than in the air. We may, therefore, venture to lay it down as a general principle, that plants evolve free oxygen in water, when in the sunlight, and remove the carbonic acid added to the water by the respiration of the animals.

But since this is a digestive or nutritive process, it follows that aquatic plants may derive much or all of their food from the water itself, or the carbon in it, in the same manner as the so-called air-plant, which grows without soil, does from the air. It is true, at any rate, that, in the fresh-water aquarium, the river and brook plants need no soil but pebbles; and that the marine plants have no proper root, but are attached by a sort of sucker or foot-stalk to stones and masses of rock. It is very easy to see, then, how the aquarium may be made entirely self-supporting; and that, excepting for the larger carnivorous fish, who exhaust in a longer or shorter period the minute creatures on which they live, no external food is required.

A very simple experiment will prove the theory and practicability of the aquarium. In a glass jar of moderate size was placed a piece of Ulva latissima, or Sea-Lettuce, a broad-leaved, green, aquatic plant, and a small fish. The mouth was closed by a ground glass stopper. The jar was exposed to the light daily; the water was never changed; nor was the glass stopper removed, excepting to feed the fish, once or twice a week, with small fragments of meat. At the end of eight months both remained flourishing: the fish was lively and active; and the plant had more than half filled the bottle with fresh green leaves.

Any vessel that will hold water can, of course, be readily converted into an aquarium. But as we desire a clear view of the contents at all times, glass is the best material. And since glass globes refract the light irregularly and magnify and distort whatever is within them, we shall find an advantage in having the sides of the aquarium parallel and the form rectangular. As the weight of the aquarium, when filled with water, is enormous,—far more than we should at first imagine,—it follows that it must be capable of resisting pressure both from above and from within. The floor and stand, the frame and joints must be strong and compact, and the walls of plate or thick crown glass. The bottom should be of slate; and if it is designed to attach arches of rock-work inside to the ends, they, too, must be of slate, as cement will not stick to glass. The frame should be iron, zinc, or well-turned wood; the joints closed with white-lead putty; the front and back of glass. There is one objection to having the side which faces the light of transparent glass, and that is that it transmits too much glare of sunlight for the health of the animals. In Nature's aquarium the light enters only from above; and the fish and delicate creatures have always, even then, the shady fronds of aquatic plants or the shelter of the rocks,—as well as the power of seeking greater depths of water, where the light is less,—to protect themselves from too intense a sunshine. It is, therefore, sometimes advisable to have the window side of the aquarium made of glass stained of a green color. It is desirable that all aquarial tanks should have a movable glass cover to protect them from dust, impure gases, and smoke.

When we speak of an aquarium, we mean a vessel holding from eight to thirty gallons of water. Mr. Gosse describes his larger tank as being two feet long by eighteen inches wide and eighteen inches deep, and holding some twenty gallons. Smaller and very pretty tanks may be made fifteen inches long by twelve inches wide and twelve deep. Great varieties in form and elegance may be adapted to various situations.

There are two kinds of aquaria, the fresh- and the salt-water: the one fitted for the plants and animals of ponds and rivers; the other for the less known tenants of the sea. They are best described as the River and the Marine Aquarium, and they differ somewhat from each other. We shall speak first of the fresh-water aquarium.

The tank being prepared, and well-seasoned, by being kept several weeks alternately full and empty, and exposed to the sun and air, so that all paint, oil, varnish, tannin, etc., may be wholly removed, the next thing is to arrange the bottom and to plant it. Some rough fragments of rock, free from iron or other metals that stain the water, may be built into an arch with cement, or piled up in any shape to suit the fancy. The bottom should be composed entirely of shingle or small pebbles, well washed. Common silver sand, washed until the water can be poured through it quite clear, is also suitable.

Mould, or soil adapted to ordinary vegetation, is not necessary to the aquatic plants, and is, moreover, worse than useless; since it necessitates the frequent changing of the water for some time, in order to get rid of the soluble vegetable matter, and promotes the growth of Confervae, and other low forms of vegetation, which are obnoxious.

Aquatic plants of all kinds have been found to root freely and flourish in pebbles alone, if their roots be covered. The plants should be carefully cleared of all dead parts; the roots attached to a small stone, or laid on the bottom and covered with a layer of pebbles and sand.

The bottom being planted, the water may be introduced through a watering-pot, or poured against the side of the tank, so as to avoid any violent agitation of the bottom. The water should be pure and bright. River-water is best; spring-water will do, but must be softened by the plants for some days before the fishes are put in.

Sunshine is good for the tank at all seasons of the year. The fresh- requires more than the salt-water aquarium. The amount of oxygen given off by the plants, and hence their growth and the sprightliness of the fishes, are very much increased while the sun is shining on them.

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.

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."46