The Modern Aquarium

Aquarium keeping in the Western World is a fairly recent hobby. The keeping of fish in small indoor tanks was seriously undertaken only in the middle of the last century, when both in Britain and on the Continent of Europe a considerable interest in the subject developed. It is not surprising that the hobby as practiced then was short lived, as the principles governing successful aquarium maintenance were little understood and their practice confined to few.

At the beginning of the present century aquarists both in the United States and in the Old World began to keep tropical fishes, and it was perhaps the essential artificiality of so doing that started a new wave of more successful fish culture. The  older aquarists were obsessed with copying nature in their tanks—or rather with the attempt to do so—whereas the keepers of warm-water fishes had to experiment with their charges and create suitable environments for them. Often they started only with the knowledge (or assumption) that the fish must be kept warm, and this in itself raised problems of quite new types, including the death of favorite weeds and water snails at higher temperatures and the more rapid fouling of water with
excess food.

Thus the aquarium gradually came to be regarded as most of us see it today, as an artifact, not a mirror held up to nature. Many had pointed out that it was a far cry from even the largest home tank to the pond or stream, and that a tank set up to resemble the latter might contain several hundred gallons of water, an old boot, a few decaying weeds, and perhaps one small fish. However, until the keeping of tropicals, it seems that  aquarists in general thought that the proper aim of an aquarium keeper was to reproduce a segment of nature.

They now realize that their task is the maintenance of a highly artificial and restricted community of animals and plants, with a balance which can easily topple with disastrous results to at least some of the members, yet which can normally be as easily maintained as long as a few fundamental facts are recognized and applied with common sense to the problems which arise.

The Rectangular Tank

In later chapters we shall see clearly why the old-fashioned fish bowl is entirely unsuited to its purpose. It has been almost completely replaced for serious fish-keeping by the rectangular glass tank, either made wholly of glass or with a metal frame and  glass sides and a bottom of glass, slate, or other rigid material. Except when used for spawning, for exhibition purposes, or as a hospital tank for the treatment of disease, the tank contains growing, rooted plants; these are set in a sand or gravel layer 1 or 2 inches thick. There may be decorative rocks, but the chief decoration is usually the plants themselves, which contribute more to the attractive appearance of a well set-up tank than do the fishes.

Such a tank is usually between 5 and 25 gallons in capacity; a 15- gallon tank measures 24 X 12 X 12 inches and is a favorite size. Smaller tanks than these cannot house many fish or allow proper development of the plants. Larger tanks are very attractive and give scope for beautiful planting arrangements and for fine growth of the fishes, but they are expensive and not likely to become generally popular. Most fanciers therefore prefer a range of medium tanks rather than one or two very large ones, but it must be emphasized that fine fishes can be grown in large tanks.

In general, tropical fishes can be housed in smaller tanks than cold- water fishes. This is because they are usually smaller and are also better able to withstand a relative deficiency of oxygen in the water. Size for size, most tropical fishes can be crowded a good deal more than the common goldfish and very much more than fancy varieties of goldfish. A 15-gallon tank might comfortably contain a dozen 3-inch rosy barbs, four or five 3-inch common goldfish at the most, and not more than a pair of Orandas of the same size.

The Balanced Aquarium

Animals (including fishes) consume solid food and excrete solid feces. They breathe oxygen and exhale carbon dioxide, and thus in total they tend to deplete their environment of oxygen and to foul it with carbon dioxide and excrement.

Plants also breathe oxygen, but in sufficiently bright light they manufacture sugars, etc., from carbon dioxide taken from their surroundings, whether air or water, and they release oxygen. This is done in the green leaf. They also absorb dissolved salts and use these together with carbon dioxide in building up complex organic compounds. Very few higher plants can utilize solid or very complex substances, and before animal excrement (usually known as "mulm" in the fish tank) is available to them it must be broken down by fungior bacteria and made soluble.

Thus plants, in adequate light, tend to restore oxygen to the environment and to remove the waste products of animals. In poor light or in darkness they deplete the water or air of oxygen just as animals do. It is only in the daytime, or under bright artificial light, that they perform the complementary function to animals.

From these facts grew the concept of a balanced aquarium, with the waste products of the fishes absorbed by the plants, and the oxygen necessary for the fishes provided by the action of the plants in light. We shall see in later chapters how this idea must be modified in practice, but the basic principle is nevertheless sound, and a well-planted tank with adequate illumination will usually stay clear and sweet for months or years with little attention.

Aquarium Plants

There are three main types of water plant of importance to aquarists—rooted plants, rootless plants, and floating surface plants.

Rooted plants are anchored in the sand at the bottom of the tank, and their leaves grow toward the source of light. Some of those most commonly used are shown here. The grass-like varieties, Vallisneria, Sagittaria, and Eleocharis, exist in many types, from  inch-high dwarfs to large plants with wide straps of leaves several feet long. They reproduce by runners, which bud off new plants, and these runners may lie along the surface of the sand or penetrate beneath it. They can also reproduce by surface flowers, but this method is of no practical importance to the aquarist.

Others such as Hygrophila, Myriophyllum, and Ambulia will strike roots from almost any piece thrust into the sand. Anacharis or Elodea, cultivated varieties of the Canadian water weed, also put out roots all over, and in nature the long growing stem is anchored by them as they penetrate the soil. All the foregoing plants are good oxygenators and absorbers of carbon dioxide, and fast growers—the two characteristics are probably quite highly correlated.

The Cryptocorynes are beautiful, slower-growing plants which can stand weaker lighting than most others and are really bog plants. They are not particularly useful as mulm and carbon dioxide users, but their splendid appearance makes them very popular, and, in addition, they last for years and gradually reproduce by offshoots from the base of the plant. Ceratopteris (water sprite) is a large, fern-like plant which is very variable in form.

The rootless plants include Ceratophyllum (hornwort), which can be pushed into the sand and then looks much like Ambulia or Myrio- phyllum, and Nitella, both very useful for spawning as they form dense masses in mid-water. Both are good  oxygenators and need good light to flourish.

Floating plants of importance are Riccia, Salvinia, and Lenma (duckweed). They are useful as top cover, where the light is too strong, and the first two plants are also used in spawning tanks, as they form dense surface masses. Salvinia and Lemna are useless for oxygenation and carbon dioxide exchange as their leaves are above water, but they absorb waste matter from the tank.

Cryptocoryne, Ambulia and Echinodorus are strictly warm-water plants, but the others mentioned above may be grown in either cold or warm tanks. Vallisneria, however, will not survive very cool conditions.

Various types of algae, either wanted or unwanted, occur in aquaria. They are practically absent from tanks which receive only artificial lighting, unless the light is very strong and prolonged. Filamentous green algae, chiefly the Cladophora types, are excellent food for many fishes and are also good oxygenators. Free living green algae are important as food for fry, but they are unwanted in the usual tank, as they cloud the water. Blue-green algae (Oscillatoria etc.) blanket other plants and may kill them. They also have an unpleasant smell and are ugly.

Mollusks

Aquarium snails consume algae and decaying vegetation. Very little damage to healthy plants is done by any commonly used species; most of them will not touch plants at all. The only obvious objection to some of the very large snails is that they may seriously foul the water when they die. A well-balanced tank can take the decease of smaller varieties in its stride, but the death of a large Japanese livebearer may be too much for it.

The common types are shown in the figure. The ramshorns (Planorbis corneus) are handsome snails, especially the red variety, which has a semi-transparent shell and a bright red body. The Australian red snail (Bulinus australianus) is of a similar color but whelk-like in shape. Other whelk-like snails are the Limnaea species, some of which are carnivorous and will help to clean up dead fish which may have become trapped and unnoticed at the rear of the.tank. The winkle like snails of the genera Paludina and Viviparus are livebearing snails, preferring cold to warm water, although Viviparus can tolerate tropical conditions fairly well.

Many fish attack snails and worry them to death. Some large fish, such as cichlids, will eat all but the big ones whole. When they can survive, they are usually worth-while additions to the tank. They are good scavengers, and their eggs or young provide an occasional tidbit for the fishes. When too much prepared food has been used, snails may save the lives of the fishes by clearing it up before the water is fouled. Their capacity in this direction is not unlimited, however. In addition, all but some of the livebearers are air-breathing and do not deplete the tank of any significant amount of oxygen. They crawl to the surface at intervals and take in air. They also absorb a little oxygen from the water, and if the tank is seriously depleted of oxygen
they will remain at the surface and so act as indicators that all is not well.

Snails should be bred in fish-free tanks and fed on lettuce leaves or other dead or dying plant material. Well-fed and quickly grown specimens have clear, bright, and attractive shells. Fresh-water mussels rarely thrive in tropical tanks, and the larger varieties are a danger in any tank. It is not always easy to check that they are alive, and they may cause havoc in a tank if they die undetected. Also, some species, such as Anodonta cygnea, the swan mussel, free masses of larvae called glochidia which clamp onto fishes and live as parasites for some months before dropping off again. This method of dispersal does not commend itself to the aquarist, who would be foolish to risk  keeping more than one mussel in a tank in any circumstances. However, as there are separate sexes, it is safe to keep a single individual. Even so, if it is a male, it may pour out swarms of spermatozoa and cloud the water. Finally, the larger varieties plow up the sand quite disastrously for carefully planned planting arrangements. The main virtue of mussels is that they keep water clear, when not engaged in fouling it themselves. They live by filtering off microscopic food particles, living or dead, and they are useful for clearing up green water. On the whole, however, it is not advisable to have them as permanent aquarium inhabitants. Much the same situation holds for marine tanks. Various species of winkle and sea snails may be used, but the larger varieties are best avoided. Most are herbivorous and will not thrive unless provided with vegetable food, which is apt to be absent from marine tanks.

Mussels may be used when small, but large mussels are dangerous for the reasons  discussed above. Their function is often better performed by small sea squirts of various species, which each aquarist must discover in his own collecting ground.

Other Tank Inhabitants

Except for the fishes and except when introduced as food, almost all other possible dwellers in the indoor freshwater aquarium are undesirable. Many prey upon fishes or the food of fishes, and some carry fish diseases. These are some insects and a few insect larvae which are harmless and could be kept with the fishes, but there seems little to commend them. Thus the great water beetle (Hydrophilus piceus) of Europe and its larvae are aquatic and vegetarian and therefore safe for fishes. Most other large water beetles are carnivorous, and so are their larvae. Various worms and Coelenterates are mostly pests and are dealt with in the appropriate chapter below. Some corresponding inhabitants of marine tanks are, on the other hand, both harmless and beautiful. Some Crustacea are perfectly harmless, but as all but the largest are rapidly eaten by the fishes they do not remain on exhibition for very long.

Fishes

Finally, we come to the fishes themselves. The main points of their anatomy and physiology are covered in the next chapter. Although this is not a book in which the various aquarium species will be described in detail, it seems a good place to outline the main families which are of importance to the aquarist and to mention some of their features. There are hundreds of families of fishes, and their exact definition varies with the authority, but those used in small aquaria number only a few dozen, and a mere eight or ten of them contain nearly all the common aquarium species.

All these families belong to the group Teleostei, or bony fishes. Those of importance are:

Characidae—a. vast family of smaller sized aquarium fishes, including the "tets," so-called because many resemble various fishes once called Tetragonopterus but now mostly renamed correctly. They inhabit Central Africa and Central and South Americamostare characterized by an adipose dorsal fin and teeth. The adipose fin is a little fat lump on the back near the tail, seen in most species, and the teeth can be felt if a needle is run along the upper jaw of the fish. Occasional species lack one or the other, but the vast majority have both characteristics. They are egg layers, and the great majority do not take care of their young; usually they will eat both eggs and young
if given the chance.

Outstanding examples of the family are the black tetra (Gymnocorymbus ternetzi), the red tetra (Hyphessobrycon flammeus),the glowlight tetra (H. gracilis), the neon tetra (H. innesi), H. serape and H. rosaceus, which have no universally common names, the head and tail light fish or beacon fish (H. ocellifer), and Riddle's pristella (Pristella riddlei).

Cyprinidae—the carp family. These fishes inhabit North America, Africa, Europe, and Asia—in fact almost everywhere except South America and Australia. They include the goldfish and relatives, various attractive minnows, and the important genera Rasbora and Barbus.

Some outstanding examples of the family are the giant, pearl, and zebra danios (Danio malabaricus, Brachydanio rerio, and B. albolineatus), Rasbora heteromorpha (usually called just rasbora or, in Britain, the harlequin fish), various other Rasbora species, and the barbs, including the rosy barb {Barbus conchonius), the cherry barb (B. titteya), the clown barb (B. everetti), the black ruby barb (B. nigrojasciatus), the Sumatra barb (B. tetrazona), and the iridescent barb (B. oligolepis).

Cyprinodontidae—the oviparous tooth carps. These are, as the name implies, egg-laying fishes with teeth. They are sometimes called top minnows, from their habit of skimming near the surface of the water. Quite a number thrive best in salty water, up to about 1/4 or 1/8 sea water strength. They are found practically anywhere on a band between the two tropics except Northern Australia and extend well into North America and South Europe. Some of the African species are very beautiful, but only under just the right conditions. These fishes do not take care of the young and usually will eat them or the eggs.

Important members of the family are Pachypanchax playfairii, Epiplatys chaperi (Chaper's panchax), and a number of others grouped under the general name panchax: the blue gularis (Aphyosemion coeruleum), the lyretail (A. australe), the Argentine pearl fish (Cynolebias bellottii), and various species of Rivulus, none of which have common names other than red, blue or herringbone rivulus.

Poeciliidae—the viviparous tooth carps. These fishes bear living young. In most of the poeciliids the young receive nourishment from their parent before birth, contrary to common belief. In the guppy, for instance, a connection is formed between the heart membranes of the young and the ovary of the mother fish, through which blood-borne food is diffused. The poeciliids are found only in Central and South America and the West Indies.

As in all previously mentioned families, the poeciliids are likely to eat their own young, although in most cases some young will survive and in some nearly all will be left uneaten, as in the mollies. The family is characterized by the ability of the females repeatedly to bear litters of young from a single fertilization—perhaps because in nature the males are the more readily eaten by other species and tend to disappear early in life.

Fishes of particular interest in this family are the guppy (Lebistes reticulatus), the platy or moon fish (Xiphophorus formerly Platypoecilus maculatus), the swordtail (Xiphophorus helleri), the mollie (Mollienisia species), and various hybrids between the platys and the swordtails, which have been so interbred that it is doubtful if any guaranteed pure stocks of either species are available except those recently caught from the wild. These fish appear in a wide variety of color combinations.

Cichlidae—largish, often pugnacious, "tough" fishes, which take care of their young in various interesting ways. Most of them guard the offspring throughout development, fanning the eggs and later herding the young into a compact swarm; some even starve throughut this period while keeping the young in their mouths. These fishes are found in Africa and in Central America; two species are found in India. In general,  they are bad community fishes,  particularly at breeding time, as they fight both with each  other and with other species and often root up plants. Only their interesting habits and the outstanding beauty of some have caused their continued popularity. There are a few species, such as the angels and Aequidens portale-grensis which are reasonably peaceful, as are also the so-called dwarf varieties mentioned below.

The angel fish (Pterophyllum scalare or P. ehnekei) is probably the most important single aquarium fish, with the possible exception of the guppy. Other important members of the family are the acaras (Aequidens species), the mouthbreeders (Tilapia species), the pompadour fish (Symphysodon discus), the jewel fish (Hemichromis b'vmaculatus), the firemouth (Cichlasoma meeki) and the Jack Dempsey (Cichlasoma biocellatum). The shy and attractive dwarfs, mostly unidentified, belong to the genera Nannacara and Apistogramma.

Anabantidae—the bubble nest builders. These fishes are found only in the tropical regions of the Old World, from Africa to the East Indies and China.

They possess an organ called the labyrinth, whichis an extra air-breathing apparatus that makes its owner independent of dissolved oxygen in the water to a large extent and thus able to live in foul pools and streams.

Air is gulped into the mouth at the surface and stored temporarily in the labyrinth. The habit of building bubble nests is a similar  daptation. The nest floats on the surface, and the eggs and young are brought into close contact with the air. The male fish guards the nest and renews the bubbles; and the family also contains a few mouth breeders like the corresponding cichlids.

Important members of the family are the paradise fishes (Macropodus species), the Siamese fighters (Betta splendens), the various gouramis (Colisa species, Trichogaster species, and others), and the climbing perch (Anabas testudineus).

The families Nandidae (leaf fishes, etc.), Gymnotidae (eels), Cobitidae (loaches), and Siluridae (catfishes) practically complete the list of families of freshwater aquarium  importance.

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