About Fishes

Not until the preparations described in the preceding chapters have been completed should fishes be obtained, and it is a good plan to let the tank settle down for a day or two before introducing them. This will not only ensure that the plants are already doing their job, but will eliminate any risk of their being disturbed by the fishes before they are properly rooted. In the meantime, it will be wise to learn something about fishes and their requirements.

Breathing

Fishes take in water through the mouth; they do not drink it, however, but pass it out backwards through the gill-openings at the sides of the head, under the bony gill-covers. As it goes through it bathes the gills, which are so constructed that they can take oxygen out of the water and get rid of carbon dioxide in exchange. The gills, then, are their breathing organs; they have no lungs. But the process of breathing is otherwise much like ours, and if there is not a proper supply of oxygen in the water, they will sicken and die.

The oxygen is dissolved in the water, and the carbon dioxide given off, through contact with the air at the surface.

Thus it will be understood that if the surface area is too small the water will become charged with carbon dioxide, and there will not be room for replacement of the oxygen when it is used by the fishes.

It has been worked out that in the tropical aquarium without aeration, the minimum surface area allowable is 10 square inches of surface to each inch of fish; in other words, one fish 3 inches long, or 3 fishes 1 inch long, will need 30 square inches of surface—an area 6 inches by 5 inches, or roughly one-tenth of the surface of our 24-inch tank. This means that the absolute maximum number of fishes we can keep in that tank is 30 at 1 inch length, or 15 at 2 inches long, or 1 o at 3 inches long; but in practice it is wise to keep below that number, to provide a safety margin. I would not suggest more than 25 inches offish in such a tank.

Cold-water fishes require twice as much surface area, so 12 inches of fish will be the most allowable in the 24-inch tank in that case.

This relationship of surface area to fish is most important, unless mechanical aeration is provided. See Chapter Two for a discussion of aeration and filtration. The use of biological (sub-sand) filtration allows the keeping of twice as many fish as recommended above, as the method continuously removes the carbon dioxide from the water.

The oxygen that the fish breathes is passed into the blood circulatory system, and so to the tissues, where it is eventually combined with elements of the digested food for the production of energy and growth (metabolism). The results of this combination are largely carbon dioxide and water, which have to be eliminated. The former is breathed out, and the latter excreted by way of the kidneys. This is all much the same as the process in higher animals, including ourselves, for the organization of the body of a fish is very similar to ours, though a little simpler.

Fins

Fishes are the lowest true vertebrates, and therefore can be compared with our earliest ancestors. They have a bony skeleton, consisting of a jointed vertebral column or "backbone", with a very complicated skull at the front end; behind the skull there are shoulder-bones supporting a pair of pectoral fins, corresponding to our arms, and beneath the abdomen there is a pair of pelvic fins supported by internal bones, representing our legs. The latter are sometimes called ventral fins, but this is not a good name, because the word ventral, when applied to fishes, means on the lower side of the body, and can be applied also to the anal fin, which lies below the tail, and is single. On the back, in the middle line of the body, is the dorsal fin, sometimes in two parts. At the end of the tail is the caudal fin; this is often called "the tail" by non-aquarists, but should at the worst be called the "tail-fin".
The true tail is that part of the body behind the vent or excretory aperture, at the end of the body-cavity.

FIG. 6
External parts of a fish (Hemigrammus nanus)

A moment's examination will show that the fins of a fish can be raised and lowered like a fan, and are supported by rays, which for the most part are flexible, or "soft". But the foremost dorsal fin, when there are two, is often supported by sharply-pointed rays known as spines; or if there are two, and the first has mostly soft rays, the second may be simply skinny or fatty, with no rays at all, and not capable of closing, when it is known as the adipose fin (Fig. 6).

The main movements of the fish are accomplished by bending the body with a waving movement, but the caudal fin may assist in driving the fish through the water, and the pectoral fins can be used to alter direction and as brakes. The pelvic fins are balancers and the vertical dorsal and anal fins are mainly stabilizers, like those on an aircraft.

Senses

A fish is provided with a brain, simpler than ours, but nevertheless more efficient than some people realize; it displays intelligence, and is capable of learning. It has good eyes -and a keen sense of smell. The general plan of the nervous system is similar to ours, though again less complex, and it is well to remember that a fish feels pain and may be shocked. Tapping on the glass, or sudden knocks on the frame of the aquarium, should be avoided, for it has a very startling effect on the fishes.

Along the side of a fish is a series of very sensitive organs, which are usually visible as a line formed by tubes in the scales. This is the lateral line, which in effect is the outer ear of the fish. It is sensitive to pressure-waves and vibrations in the surrounding water, and conveys them to the brain. There is an inner ear surprisingly like our own, but concerned mainly with balance, so far as we can tell.

Blood And Temperature

The blood of a fish has approximately the same temperature as the surrounding water; when the water gets warmer or colder, so does the blood. That is why fishes are more active at higher temperatures, for a certain amount of heat is necessary for metabolism to take place. They also get more hungry as the temperature rises, because food in the tissues is being used up. It is also the reason why it is desirable for the temperature to be lower at night, so that the fishes can rest.

The changes of temperature, however, must always be slow, to give the blood a chance to keep pace with it. A sudden change of temperature of more than two degrees is dangerous to fishes. You will see therefore that there is a difference between temperature range, varying over a period of hours, and temperature change, altering suddenly, perhaps the difference between the receptacle in which the fish is carried and the tank, or perhaps the result of pouring a quantity of cold water into a warm tank. The fish can adapt itself to, and actually benefit by, a range, but may be killed by a change. This is a very important thing to bear in mind.

While on the subject of the blood, it may be useful to mention that in freshwater fishes it contains a higher proportion of salts than the surrounding water. As a result, by a process called osmosis, the tissues tend to absorb water and so dilute the blood; to counteract this, the kidneys must get rid of the water and save the salts. So changes in the salt content of the surrounding water will react on the organization of the body, and this can often be used when treating a sick fish, as will be seen in a later chapter. But it also means that we have sometimes to be careful of the water we put in the tank, for some kinds of fish are more sensitive to osmotic changes than others, and may be harmed by living for a long time in "hard" water, that is, containing a comparatively large amount of lime salts. You need not worry about this in the early stages, but it may be worth knowing later on.

Air-Bladder

Most fishes with which we are concerned have a delicate vessel in the body-cavity, which is kept full of gases derived from the blood; this is partly an accessory breathing organ in some fishes, being often connected with the gullet, while in most it serves to make the body lighter, so that it floats in the water at the required level. For the latter purpose the amount of gas can be altered, and the first sign of some disorders is the inability to make the alteration, so that the fish loses its stability.

Growth

Theoretically, fishes continue to grow throughout their lives, and so it should always be possible to get larger specimens by improving their conditions. In fact there is generally a range of size characteristic for each species; some normally grow large, others normally remain small. The smaller ones are usually most suitable for aquaria. Round about this normal range, however, many factors have a bearing on size; lack of food, poor water conditions, breeding too early, or constant high temperature, for example, may mean that the fish never reaches the expected average size, while improvement of such conditions may cause it to exceed it.

One very important factor in this connection is the size of the aquarium. It has been proved over and over again that a fish in a large tank will grow larger than one in a smaller tank, even though all other treatment is exactly the same. We do not know the reason for this, but it is a valuable piece of knowledge.

In any given brood of fishes, there will be a number which do not grow as well as the others; these usually become apparent after a week or two, for not only do they remain smaller than the others, but they often get a more adult look while still so tiny; some of them are often bent or deformed, also. These are usually called "runts", and should be destroyed, to make more room for those that will grow normally.

Generally, growth slows down considerably when the fish starts to breed, as the energy is diverted into the production of young; so to make a big fish it is advisable to keep the sexes apart for as long as possible.

The age to which fishes will live is variable. Some, like the Guppy, rarely exceed two years, while others, like the Cichlids, may live for twenty or more. For a great many species no records are available.

Choosing Fishes

After studying the account of the various kinds of fishes, which is given in the next chapter, you will visit the dealer to make your purchases. It is necessary to give warning here that many varieties of fishes are known locally by a common name and not by the scientific one.

In selecting your fish remember that large pugnacious fish should not be kept with smaller, timid ones, and some of the smaller "barbs" will soon kill off your beautiful "angels". Start your aquarium with fish all about the same size. If some grow larger, at least the smaller ones will not be intimidated by them from the beginning.

Look carefully at the stock, and make sure that the fish is quite clean—free from blemishes on the body, and without damage on the fins. Look particularly to make sure that there are no white spots, about the size of pinheads, on the fish, and no brown velvety growth, for these are diseases. I must hasten to add, however, that reputable dealers are careful not to stock diseased specimens.

With tropicals, it is better to get young specimens, as they are more adaptable, and less affected by transportation and changed conditions. With Goldfish, it is generally not advisable to get anything less than a year old, as it is not likely to show its color earlier, and there is no guarantee that an uncolored fish will eventually color up.

Healthy fishes hold the dorsal fin erect and well spread, and swim evenly and easily. Fishes out of balance, swimming jerkily, or with drooping fins, are usually sick. A few tropical fishes have unusual swimming methods, or adopt curious attitudes when in repose; these will be noted in Chapter Seven.

As a beginner, it will probably be best from all points of view if you choose livebearers such as Platies, Swordtails or Guppies, as these are very hardy, colorful, and easily bred.

Small fishes can be carried safely in screw-topped glass jars which, if only half full, will contain enough air for some time; in cold weather they can be wrapped up and carried in a bag or even in the pocket.

Larger fishes will require a metal can; most dealers supply these at a small charge; they need to be wrapped round with felt or other insulating material, and paper in cold weather.

On arrival home, the jar should be opened, and floated in the aquarium, so that the water in it takes up the same temperature as that of the tank. Never tip fishes straight from one temperature to another. The temperature of the tank will have to be adjusted to that of a fish can, by the addition of hot or cold water, before the fish are transferred. Never handle them—or if you must, always with a wet hand—but use a net. Aquarium nets of various sizes are cheap to buy, or easily made (see Chapter Eight). Small round ones are useful for taking fish out of round cans; rectangular ones of various sizes for the rectangular tank. Do not drop fishes into the water with a splash; put the net in the water and let them swim out.

Prices

The prices of fishes and plants are subject to the laws of supply and demand and fluctuate accordingly. Stock is naturally rather shorter and more expensive during the winter months. The commoner kinds, however, and particularly those bred largely in captivity, are usually in good supply, and as these are most suitable for beginners, the initial outlay is not likely to be great. Prices for the species listed in the next chapter range from .35 to $5.00 per fish, except for the fancy goldfish and real rarities among the tropicals, good specimens of which may cost very much more. A number of "classy" tropicals bought only by connoisseurs at fancy prices (and often lost soon after) have been left out.

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