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Natural Fish Tanks

The natural history of fish dictates the environment they need in an aquarium.

By Richard Thompson

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When you walk into a tropical fish store with the intention of selecting fish for your aquarium, you have a lot to think about. What fish do I want? Is my tank the proper size? Do I have sufficient filtration? Is the tank in a suitable location? Do I have enough light? These and other questions are important and need to be answered.

In my experience, however, some hobbyists — particularly beginners — can become overly concerned with information that is of little importance at their level of involvement in the hobby. Often, this is the result of listening to some well-meaning friend or neighbor who is also a hobbyist. Eager for information, the novice will absorb what he or she hears, unaware that its value may be limited to the problems encountered in one individual's tank.

Sometimes, beginners become so obsessed with what they have learned that they fail to see the real issues in fishkeeping. This is unfortunate, because it is essential that new aquarists understand what they are actually trying to accomplish. A fishkeeper's ultimate goal is to provide an environment for their fish that is as close as possible to the natural environment from which they came.

The bottom-line question that the hobbyist should therefore ask is: How do I go about creating the proper environment for my fish? That question then leads to an even more fundamental question: What is the natural history of the fish I am keeping? The purpose of this article is to help you think about the factors than constitute the natural environment of a fish.

Aquarium Layout
We will begin with the assumption that the fish you would like to keep are suitable for the size aquarium you have. Thus, your first task is to determine the best way to set up the aquarium for these fish. This is crucial, because it is quite possible that the environment you would like to keep the fish in differs significantly from the environment the fish should be in.

As an example, let's consider the various fishes that make up the genus Nothobranchius, a popular group of killifish. These egg-laying toothcarps are usually found in still waters, such as ponds and lakes, that dry up — partially or completely — during the dry seasons in the countries where they are found. As you can imagine, these fish do not require a great deal of room. They have evolved to survive in aquatic environments that are reduced substantially in size during prolonged periods of dryness. The ponds they are found in are wide but fairly shallow. An aquarist can utilize this information when selecting an aquarium to house these fish. In this case, a wide but somewhat shallow tank will provide the fish with a home that has a relatively large surface area, maximizing the exchange of oxygen and carbon dioxide. It would be a mistake to place these fish in a tall, relatively narrow aquarium, which would have a much smaller surface area.

When aquascaping an aquarium, you should give serious consideration to the type of gravel that will be used. The choice of substrate should be dictated by the fish being kept. Most cichlids, for example, especially the larger species from Africa, South and Central America, love to move, dig and channel the substrate. One look at the mouth structures of cichlids and you can see why they are efficient gravel movers. Therefore, when choosing gravel, it is better for the fish to have a thick layer of smooth pebbles, similar to their natural habitat, rather than sharper, coarser stones that can possibly injure mouth parts and result in infection or permanent damage.

An effort should also be made to find out what types of plants are native to the waters of the fish that are being kept. These plants are often vital to fish in their natural habitats. Some fish use plants as a spawning medium. Two examples are neon tetras (Cheirodon innesi), which prefer to scatter their eggs among the leaves of java moss, and angelfish (Pterophyllum sp.), which utilize the broad leaves of various Amazon sword plants to lay their eggs on. They will also deposit eggs upon other hard surfaces, but these particular plants are preferred.

Plants are often an important part of a fish's basic diet. In addition, plants provide shelter and protection from predators. In some instances, certain plants give off substances that have a bacteriostatic effect, protecting fish from various bacterial infections.

On the other hand, there are plants that may be inappropriate for some setups. For example, you would not want to place certain plant species, such as bladderwort (Utricluaria vulgaris), in a breeding tank for livebearers, because the bladderwort would efficiently trap and ingest the baby livebearers. Another consideration is whether bog or driftwood should have a place in your aquarium. Keep in mind that some fish naturally use this wood in the wild as a spawning area, as shelter or as a boundary for an established territory.

Another consideration is the type of rocks to use in the tank. Some hobbyist books contain pictures of aquarium fish in their natural environments, and these photos can be used to discover the most suitable kinds of rocks for a species of fish. For example, fish that are used to swimming close to smooth rocks might suffer injury if placed in an aquarium with lava rock, which has a rough surface. Photos can also help you place the rocks in a natural configuration to provide shelter, territorial barriers or areas in which the fish can spawn. You should also take into account the chemical composition of the rocks. Some materials will react with water and cause it to become harder or softer. Your dealer is a good source for information on the appropriate rocks for aquascaping and can make recommendations based on local tap water conditions.

Water Quality
In this section I will cover three important points to consider when trying to duplicate the natural conditions and water quality values of the fish's natural environment in your aquarium. The first and sometimes easiest value to deal with is the temperature requirement for each species of fish. One reliable source where a hobbyist can obtain this information is the pet store where the fish were purchased. Knowledgeable store owners or sales staff members should be able to tell you the temperature range for the fish you are keeping. In addition, books written about your particular species of fish or any of the large compendium volumes (atlases and encyclopedias) can be of help. Specific articles about your fish in this or other aquarium magazines may also be valuable.

It is important to realize that there is no one specific temperature for each species of fish but rather a temperature range. This range takes into consideration the water temperatures at the time of year a species is collected, optimum breeding temperatures and other weather-related influences on water temperatures. In the wild, fish commonly move through different pockets of water that vary in temperature from each other. For example, a fish can move from a shaded area along the bank of a stream to a brightly lit area, with a difference of as much as 4 degrees Fahrenheit between them. Yet, the fish suffers no ill effects. New hobbyists are often so set on keeping exact temperatures in their tanks at all times that they fail to recognize that fish in the wild are well-adapted to small changes in temperature.

The concern about fluctuating temperatures is understandable, of course. Many fish disease are brought on by the stress of sudden drops in water temperature. These include white spot disease, shimmies and other maladies. What aquarists should keep in mind is that problems will start if temperature changes are extremely sudden and drastic. Fish in the wild adapt readily to smaller changes in temperature, which occur as a result of various environmental factors relating to the weather. Indeed, sometimes small shifts in temperature can induce some species of fish into spawning.

The second water quality value to consider is pH. Without going into a long explanation about pH and what it is, it can be said that the pH of water can be extremely critical to the overall health of fish, for several reasons. While there are many fish that are not particularly fussy about the pH of the water, numerous species of fish require specific pH ranges simply to exist. African cichlids, which must be kept in a pH range between 7.4 to 9.0, depending upon the species, would surely perish if they were kept at a level below 7.0. On the other hand, a pH of 7.0 is quite suitable for most species of tetra. The pH value of water in the wild is strongly influenced how much rain the area receives, what the basin and the walls of a lake, stream or pond are made of, and the type of leaves falling into that body of water. The resulting pH range in nature indicates what the acceptable pH range in an aquarium is for each species of fish.

A third factor is the softness or hardness of water, which is measured in degrees of hardness (DH). Although hardness is related to pH, it does not have a scale as universally accepted as the pH scale — that is, there are actually several methods for measuring the hardness of water. Hardness is the amount of solids and minerals dissolved into water. Usually, water that has an alkaline pH (above 7.0) has a high DH, and the reverse is generally true for water that has an acidic pH (below 7.0). The environmental factors that influence the pH of water in nature also affect hardness. It should be kept in mind that while there are a number of materials (ion exchange resins, peat, liquid water softeners) that are available to alter the hardness and pH of aquarium water, they should be used with care. Rapid or drastic changes in these values can be fatal to the fish in an aquarium.

Lighting
The lighting requirements for fish are almost certainly going to vary from species to species. An aquarist has to take into account a number of factors. These include the depth at which a species is found, weather conditions (does the collecting area receive abundant sunlight or is it cloudy) and the quantity of leaves and other organic material that are present in the water, which determines the amounts of tannic acids given off by the decaying vegetation and thus the degree of brownish tint to the water.

Lighting can affect the behavior of your fish in a positive or negative manner, depending on the species. Too much light in a tank that contains species that are used to low light levels may put undue stress on them. Sometimes too little light will cause other species to be more introverted, putting them at a disadvantage when competing with tankmates for food or territory. For shyer species, the addition of peat, black water treatments and other prepared solutions may help in providing diffused light, making these fish more comfortable. Stronger, more intense lighting may be needed for fish that are used to living in strong daylight in the wild.

Feeding
Feeding can be a very tricky aspect of fishkeeping to master. A good example would be the situation of an aquarist contemplating the purchase of a particular fish that is fond of mosquito larvae and not much else. The hobbyist is faced with the burden of whether to purchase the fish and attempt to get it to eat only what he or she has on hand, or cater to the fish's requirements. Thus, the aquarist needs to determine what the fish's dietary requirements are and whether it will be possible, and sufficiently convenient, to provide the food or foods that are necessary.

When in doubt as to the types of foods to feed, it helps to examine the structure of the mouth of the fish. The anatomy of the mouth and its placement in relationship to the head is an indication of probable feeding habits. An excellent example of this can be seen in the Geophagus species. The mouths of these fish are angled down toward the substrate. They utilize their mouths by digging up and spitting out gravel, searching for scraps of food and tasty live morsels. Fish with mouths that are angled upward generally feed from the surface of the water and will do best on foods that float.

This article has only touched on some of the aspects of the natural history of fish and how it relates to fishkeeping. The purpose is to encourage aquarists to think about how the natural environments of fish indicate the conditions that are needed in a closed aquatic system to maintain each species correctly. Although it is impossible to duplicate a fish's natural environment, we can make every reasonable effort to come as close as possible to providing the best artificial environment for each fish in its new home.

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