A NEXT DOOR NEIGHBOR who normally makes a fetish of getting a full night's sleep rang our telephone at the outlandish hour of 2:00 a.m. in the morning. "My angel is laying eggs!" he exclaimed. "What should I do?" Our friend was referring, of course, to Pterophyllum scalare, otherwise known as the angelfish. We advised him to go to bed and let nature play midwife. As experienced keepers of tropical fish know, there was nothing else he could do. When conditions in the aquarium are proper for spawning-when the tank is clean, slightly warmer than usual and free of competing species-well-fed angle fish do not eat their eggs as a rule. If these requirements have not been met by the time the eggs arrive, you may as well relax and observe how nature disposes of potential weaklings.

Tropical-fish keeping does not involve much work-which is a major reason why it has become the third most popular hobby in the U. S. According to Leonard Berkitz of the Aquarium Stock Company in New York City, only photography and stamp collecting outrank tropical fish in popularity. About 20 million persons in this country have home aquariums. They spend some $70 million a year on their hobby and support a billion-dollar industry. Hundreds of commercial collectors search the tropical streams and pools of the earth for marketable specimens. One South American exporter maintains a large twin-engined airplane for the exclusive purpose of transporting miniature fish to New York City. The investment of individual fans ranges from as little as $5 (which the novice next door had laid out for his small tank and lone pair of angels) to as much as $35,000, which a New York businessman spent last year to decorate his Park Avenue duplex in a motif of recessed tanks filled with hundreds of rare specimens.

The average fan devotes about 10 minutes a day to his fish, but you may invest a great deal more time (and ingenuity), particularly if you enjoy the biological sciences. For $15 or $20 you can buy a dozen fish along with a handsome tank, plants, food, sand, an automatic filter, an aerator and a complete assortment of gadgets for handling the fish and keeping the tank clean. This fits you out with all you need for studying these fascinating bits of life in endless ways as they emerge from the egg and progress through courting, fighting, mating and old age.

With tens of millions of enthusiasts exploring the ways of tropical fish, one might suppose there is not much to find out that is not already known and published in reference books. Actually the books don't begin to answer all the questions that a curious amateur scientist will ask as soon as he becomes acquainted with his aquarium. The study of behavior alone can be a lifetime avocation, particularly if you go in for unusual fish. How, for example, does the weatherfish sense approaching storms? Just before a downpour it rushes around the aquarium in a frenzy. Experiments indicate that its agitation is triggered by changes in barometric pressure. If so, what part of the fish's body acts as the sensor and what advantage does the adaptation give the species? An aquarium fitted with an apparatus for varying the air pressure on the water might lead to interesting results. Then there is the archerfish, which shoots pellets of water with rifle-like accuracy at flying insects. It can score a bull's-eye on an insect a foot or more above the aquarium, although its eyes are below the water surface. How does the archer compensate for the refraction of light at the surface? That this is an important problem is shown by the fact that one species, an Anableps, is specially equipped with eyes divided into two parts, of which the upper part can adjust to seeing in air and the lower part to seeing in water. Other species of fish have periscopes, and at least one fish possesses a telescopic eye which should fascinate amateur astronomers.

Not many amateurs can afford these odd and comparatively scarce specimens. Most start off with guppies-the humble commoners of the tropical-fish world. In the past two decades geneticists have transformed the once-drab guppy into one of the most colorful creatures in the aquarium while using it as a subject for experiments in heredity. They have produced a number of attractive hybrid strains, particularly the platy-swordtails which appeared as byproducts of Myron Gordon's researches into the genetic aspects of cancer at the New York Aquarium.

What is the best diet for fish? This is another area of great interest among fish fans. The cliche among ichthyologists is that "the best food for fish is fish." Doubtless the rule holds for fish in the wild state. But most authorities now agree that it breaks down when fish are confined to an aquarium. Conditions in a tank are so different from those in tropical streams and pools that only a few hundred of the most hardy specimens survive shipment.

Leon F. Whitney, a veterinarian and authority on the guppy, recently made a start on the food question by measuring the proportion of water to dry matter in eight types of food usually given to tropicals. He found a great variation in the solid content of these foods-as much as 20-fold. The dry matter in Tubifex worms, Daphnia, bloodworms and brine shrimp ranges from about 4 per cent to 14 per cent; white worms average 23 per cent; commercial preparations (such as crushed dog biscuit) go as high as 93 per cent. These figures indicate why it is easy to kill fish by overfeeding when you give them dried preparations. Furthermore, there are many other things to consider besides the amount of solid content. Fish need certain percentages of fats, carbohydrates, proteins, vitamins and minerals. To keep them healthy, they should also have live food occasionally: dead worms, even if relatively fresh, fail to supply as much of some mysterious something as do worms that go into the tank alive. What element vanishes with the worm's death? Here is a challenging problem for an amateur with a background in chemistry.

Equally subtle is the relationship between the fish and the water in which it swims. Christopher Coates, curator and aquarist of the New York Aquarium has pointed out that fish tend to establish a chemical harmony between the fluids in their bodies and those in the tank. By a kind of osmotic interchange the water in the tank becomes increasingly like that in the fish and vice versa. Thus each fish conditions its aquarium, so that in time you wind up with "guppywater" or "swordtail-water," depending upon the species in the tank.

The fluids of most species of tropical fish kept in aquariums differ only slightly, so they can inhabit the same tank. But some are antagonistic to one another. You can observe this by watching a tank with a mixed population, at the same time keeping individuals of these species in separate tanks for comparison. The fish in the separate tanks will grow faster and do better generally. In the mixed community, after a time, some fish will lose their vigor, some will lose color, some will fail to reproduce. As the experiment progresses, it becomes clear that certain species are gaining the ascendancy, while others are dying out. Eventually you may be left with only one kind of fish in the tank.

The fish are also in competition with microorganisms that drop in from the air, arrive with the food, and so on. Some microbes infect them with disease. Others may be helpful, but recent experiments indicate that on the whole the fish would have the best chance of survival if they could live in an aseptic aquarium. Experimenters have raised fish of remarkable size and vigor by supplying antibiotics to the water continuously from the egg stage to maturity. How much of the result is due to the suppression of microorganisms and how much to the influence of the drugs on the organic processes of the fish has not been determined. The answer may come from an experiment now under way at several research institutions. Fish are being reared under sterile conditions. Eggs taken from the female by Caesarean section are sterilized in a solution of formalin arid incubated in. water hot enough to kill microorganisms. All the fish food is similarly sterilized. Preliminary reports indicate that giants are emerging from the experiment-fish twice the normal length and four times the weight!

Joel Rodney, a Brooklyn high-school boy who makes a hobby of chemistry, undertook a series of experiments in the opposite direction. He tested fish in water polluted by industrial wastes.

"Two years ago," he writes, "I came across an article in the New York Times which discussed the seriousness of pollution in Lake Michigan, particularly in the region of Chicago. I asked a friend who lives on the North Shore to bottle a sample of the lake water for me. Subsequent analysis showed a high concentration of magnesium chloride. I wondered whether the concentration was strong enough to kill fish native to Lake Michigan, but since I was a thousand miles from the scene, I had to settle for experiments that could be tackled in my bedroom.

"My subjects were guppies, which bear their young live, and the African mouthbreeder (Tilapia macrocephala), a species that lays eggs. Starting with six pairs of ordinary guppies, I bred several hundred within a few months, and from this stock I selected 108, ranging in age from two weeks to three and a half months. I divided them into 18 groups and placed each group of six fish in a glass jar containing three pints of water with a certain concentration of magnesium chloride. As a control, I also had two jars of guppies with uncontaminated water. All the fish were kept at a uniform temperature of 72 degrees by means of a 60-watt lamp bulb a few inches above each jar, which precisely compensates for the 10-degree nighttime drop in our thermostatically-controlled apartment, I raised some Tilapia in the same way; since they did not reproduce nearly as rapidly as the guppies, I had only five jars of them for the experiment, plus one as a control.

"I dried magnesium chloride over an open flame and then introduced a measured amount, weighed on an analytical balance, into each experimental jar, first dissolving the salt in a little water. I started with a concentration of 100 parts per million in the first jar, watched for the reaction of the fish, and successively increased the dose in the following jars, up to 50,000 parts per million. For the guppies the minimum lethal dose proved to be 8,000 p.p.m. The 50 cent lethal dose (killing half the fish was 20,000 p.p.m. For Tilapia the minimum lethal dose was 1,000 p.p.m. and the 50 per cent lethal 4,000 p.p.m. Tolerance for the poison increased with age; the oldest fish could withstand six times as high a concentration as the youngest [see charts Figure 3].

"After the experiment had been running a few weeks, I learned to predict probable mortality by observing the behavior of the fish when the poison entered the water. Hardy specimens tended to swim around the tank, at a slightly faster than normal rate. Those more affected swam in a figure 8. The most injured darted up and down between surface and the bottom of the tank. You often note erratic behavior like this on transferring fish from one tank to another. When I commenced working with fish, I supposed they behaved that way because of fright aroused by the handling. Now I wonder whether chemical differences in the water may not account for it, at least in part."

Rodney's paper describing this work won a Westinghouse Science Talent Search award, landed a summer job for him with the American Museum of Natural History and helped win a scholarship under which he is now studying at Brandeis University.

A design for an unusual indoor sundial has been submitted to this department by Rear Admiral Garret L. Schuyler, U.S.N. (Ret.) of Washington, D. C. His dial also serves as a calendar, occasionally as a wind vane and as a novel decorative scheme for your den, should your taste run to abstract art [see Figure 4].

"First select a window sill which gets direct sunshine for a couple of hours each day," says Admiral Schuyler. "Inside the window, and well back on the horizontal sill-surface so as to avoid the shadow of the bottom of the window frame when the sun is low in winter, stick a 5/8-inch-square mirror face upward, using Duco cement. The sun's rays will be reflected upward from this small mirror and, even if they should have to pass through a light rayon curtain, they will make a small, roundish spot of light which travels across ceiling as the sun's position shifts.

"At some selected time of day, say noon, mark the position of the image on the ceiling with a tack or an inconspicuous cross. Record the date with this mark. Repeat the process at weekly intervals as the seasons change and the sun travels north or south. Now if you draw a smooth curve on the ceiling through all the marked points, you will be able to tell noon of each day as the moment when the sun's image touches a point on this line. If you also mark its position on the curve on the first day of each month, you can closely estimate the day of the month from the image's crossing on any day.

"Such a curve, labeled 'analemma' and marked with the months of the year, is-often reproduced on geographical globes in the conveniently open area of the Pacific Ocean. Our curve on the ceiling is this same analemma-reversed by reflection, distorted by oblique projection on the ceiling, and modified by two sudden displacements where the time changes from 'Standard Time' to 'Daylight Time' and vice versa. But even though the mirror is canted and the ceiling may be somewhat irregular, the method described will establish a time-of-day curve without resort to mathematics or the usual correction devices required by sundials.

"A single line is perhaps all that many persons will want, but by constructing a series of lines corresponding to the hours and quarter-hour intervals one can readily make a complete sundial. Care must be taken, however, to distinguish the parts of the lines which are traced when the sun is traveling south (June to December) from those when it is traveling north (December to June). One set of markings may be traced by solid lines and the other by dotted lines. In practice it is convenient to use Scotch tape for marking the lines, one set in red tape and the other in black. The resulting design is both attractive and easy to read. The design's interest can be heightened and its utility doubled by making two sundials: one from a south window and one from a west window of the same room with the lines crossing.

"The traveling spot corresponds to the sun's image in a pinhole camera, the 'pinhole orifice' being replaced by the small mirror. At

close range the spot is somewhat rounded but the same size as the mirror. Farther away the width is approximately equal to the diameter of the mirror multiplied by .009 times its distance from the mirror. At 10 feet the 15-minute lines will be spaced about 10 inches apart. Time can easily be estimated to the nearest minute.

"If you watch carefully, cloud formations can often be seen drifting across the sun's disk. Thus the indoor sundial acts as a vane showing the direction of the wind. This effect could doubtless be heightened by inserting a spectacle lens of appropriate focal length in the beam -but I have not added this refinement.

"For a shut-in person, or for anyone persistent enough to pursue the project for a whole year, we can think of no easier or cheaper hobby than constructing time-of-day lines for sundials of this sort. And between the convenience and comfort of reading an outdoor sundial in wintry weather and reading one on the ceiling, we submit that there can be hardly any comparison."

Bibliography

ALL ABOUT GUPPIES. Leon F. Whitney. Garden City Books, 1952.

ORAL INCUBATION IN TILAPIA MACROCEPHALA. Evelyn S. Shaw and L. R. Aronson in Bulletin of the American Museum of Natural History, Vol. No. 5, pages 381-415; April, 1954.

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