Feeding Fishes

The food requirements of fish have not been studied in detail as have those of man and the domestic animals. It is not surprising, therefore, that a lot of research must be done before we can be very certain of anything. Relatively vast numbers of reports have been produced on the feeding of some of the laboratory animals used in scientific research, such as the guinea pig and the rat, and yet there are still many problems about the exact vitamin and mineral requirements, the roughage volume needed, and so forth, even for these intensively studied creatures.

We do not know for certain which of the known vitamins are required by fishes, or whether there are likely to be unknown vitamins not yet discovered which they need. We can guess that vitamins of the B group are almost certainly needed, as they are of primary importance to most higher organisms, but it is quite likely that the rest do not matter. We know little about the detailed protein, fat, or carbohydrate needs of fishes; although it is sometimes stated that they cannot digest fat, even this belief would seem to be a mistaken one, since their natural foods, such as plankton, often abound in fat. Presumably they need a balanced intake much like our own, as they must build up a very similar body structure, but we know none of the finer details.

These facts are of little practical importance as long as we can supply natural food to the fishes. Too often we cannot, and then it is desirable to supply as near a copy as we can, or to substitute foods which have been shown by experience to produce satisfactory results. The requirements may be different for breeding from those needed for mere healthy maintenance in a community tank.

Natural Foods

Nearly all fry feed on plankton, which consists of single-celled organisms (infusoria), insects in young stages, Crustacea, and worms and other water creatures, or even other young fish. The size of the food they eat depends on their own size and mouth capacity. Very small fry in the early stages consume the smallest single-celled algae and ciliates, graduating later to the larger single-celled animals and plants and then to multi-celled creatures. Such fry are those of the Siamese fighter (Betta splendens) and many other anabantids. Larger fry, such as those of the barbs, can start further up the scale.

Older fishes vary more in their natural foods, and many have a considerable omnivorous capacity. Characins are mostly  carnivorous and feed on insects, Crustacea, snails, and other mollusks, or on other fishes small enough to be swallowed. Some eat vegetable matter by choice, such as Hemigramrnus caudovittatus, and many will eat it if they have to do so. Cyprinids are omnivorous, taking both animal and vegetable food, with a preference for the former if they can get it. Many get along quite well with little but vegetables, however, particularly the carps and the barbels. A recent survey of the food of Indian barbs showed that algae and diatoms (small, shelled plants) formed their main diet, although in five of the nine species studied crustaceans were also eaten. In the aquarium, these same fishes would probably get along better with meatier food.

Cyprinodonts feed mostly on surface insects, crustaceans, worms, fry, and other fishes. They will eat dead vegetable food only if they have no choice, and the extent to which they do this in Nature is not reported.

Poeciliids like algae and other water plants, and they also like practically anything else. They seem, however, to need a supply of live vegetable food for best health and reproduction.

Cichlids, anabantids, and practically all the rest of the aquarium fishes are carnivorous by preference and omnivorous by necessity. Some gouramis need algae—the kissing gourami (Helostoma temminki) in particular. The larger members of these families are particularly likely to be carnivorous and predatory—i.e., active seekers and eaters of living animals, including other fishes.

Most of the above fresh-water fishes can become accustomed to very different foods from those obtained naturally and thus can be successfully kept or reared in the home aquarium. Others are more choosy and will not learn to eat dried food, or even dead food. They are fortunately rather few, but include Badis badis, some of the sticklebacks, and Belonesox.

Marine fishes are more likely to fall into this class, although a surprising amount can be done to wean them to dead, if not dried, food. The Syngnathidae (sea horses, etc.), however, will never take anything but live foods and not many varieties of those are accepted.

Dried Foods

Aquarists are well supplied nowadays with an overwhelming choice of tinned or preserved foods. Many of these are excellent, and as long as the fishes will take them and appear to thrive they may be used with confidence as the staple diet. It is unwise to use only a dried food, simply because we can never be sure that any one of them contains all that is needed for health or reproduction, until we know that one does, live foods must also be used as frequently as possible. There is no reason why a dried food for constant use cannot be produced, once we know what to put in it and how to vary it for different species. There is a lot of nonsense written about the need for a varied diet to keep fishes healthy and "happy." Variety is advisable only because of our ignorance; if we give a bit of this and a bit of that, we are less likely to be depriving the fishes of some essential component of a balanced diet. When we know much more, as we do for the mouse, we can give a constant mixture month after month with results as good as, or better than, any variety in feeding produces.

There are bad foods, consisting mostly of powdered biscuit or bran with perhaps a little "smell" added. They are not very difficult to detect, and they are not offered by reputable firms or dealers. On the other hand, there is no need to go to the expense of very fancy foods containing costly items which probably tickle the human palate much more than the fishes' palates. A good all-purpose dried food is of a fairly uniform particle size, appropriate to the type of fish, and contains a proportion of between 30 and 50% of animal material, preferably dried shrimp or other Crustacea, and not much actual dried fish or meat other than liver, preferably beef liver. Its vegetable component is preferably a breakfast cereal of the flaky variety, containing the heart or "germ." It also contains adequate mineral supplements, notably a little common salt and calcium phosphate, particularly if the water is soft. Such a food can easily be made at home.

Most fish culturists who manufacture their own food do so by taking such a mixture and adding egg and water, or flour and water, making a stiff paste which is then dried and ground to convenient sizes. This seems rather unnecessary, and it is perfectly satisfactory to buy a tin of cereal and a tin of dried shrimp, or to dry and pulverize your own shrimp, and then to mix them. Such home-made foods are worth making only if you keep fish in quantity, for they are then much cheaper than ready-made varieties, and you know what is in them. Half a teaspoon of salt and 1 to 2 teaspoons of calcium phosphate (tribasic) to a pint of the mixture completes the preparation.

A food recommended by Gordon, in an excellent chapter on fishkeeping in The Care and Breeding of Laboratory Animals edited by E. J. Farris (John Wiley and Sons, New York) is made from:

Liver or beef	5 pounds
Pablum or Ceravim	14 pounds
Shrimp shell meal	6 pounds
Shrimp meat shredded	3 pounds
Spinach	3 pounds

The raw beef liver is cut into 2-inch pieces, boiled for 15 minutes, then removed from the water. The same water is used for boiling the other ingredients, while the boiled liver is ground or chopped and returned to the mixture for a further 15-minute boiling. The paste is dried and ground for storage.

For feeding fry, fine food may be made from coarser supplies by grinding them in a pepper mill, or by crushing them between flat tiles and then sieving carefully. Such food for young fishes preferably contains more animal material and may be made from 100% dried shrimp  or crab.

It is a frequent practice to float a "feeding ring" on the surface of the water when using dried food. This is a small ring of hollow glass or plastic which confines the food to a portion of the tank and makes it easier to remove unconsumed portions.

Other Prepared Foods

Most fishes like the various baby foods, or porridge. Porridge may be made as for human consumption, but preferably with a little dried shrimp mixed in with it. Serve it in small soggy lumps, and expect to have to clear up the tank afterwards unless you gauge the fishes' appetite very precisely.

Canned crab or lobster, fish roe, canned spinach, and other nonspiced canned foods are much appreciated. The cold-water fishes, mostly heavy eaters, are particularly fond of chopped-up canned foods of this description and may conveniently be fed frequently on them.

Fishes also eat egg in various forms—as an omelette, boiled and chopped up, or poured into boiling water and beaten as it solidifies. They readily eat meat, particularly minced heart or liver, but this should be fed only occasionally, as it seems to produce intestinal troubles if used much, resulting in thin fish and fouled tanks. Goldfish may be fed almost anything from the kitchen that is not spiced or oily —because the oil spreads as a film over the water, not because it is indigestible or otherwise harmful—but any food must be fresh and of suitable size. Finally, fishes like fish, fresh, cut up or minced, or boiled and shredded. However, too much raw fish has vitamin-destroying properties and should be avoided.

Live Foods

The conscientious aquarist who likes to keep his fishes in the best of health and who wants to breed them frequently probably spends as much time in collecting and culturing live foods as on anything else. Only a very fortunate man can obtain as much as he really feels his fish need, particularly in winter and particularly if he lives in a town and keeps many fishes. Live foods are not absolutely essential for all species, but they are always desirable, and breeding is unlikely without them except in the livebearers and a few hardy egg-layers. The spirit and appearance, to say nothing of growth rate, of fishes reared entirely on such prepared foods as are at present available leaves much to be desired in the great majority of cases. On the other hand, entirely live diets are quite unnecessary except in the few instances where the fishes won't eat prepared food. Something in the neighborhood of 40 to 50% of live food seems to give as good re- sults as 100%, and, if an attempt to feed only live food means reduced rations, fish on prepared food may do better.

EARTHWORMS

The earthworm holds an important place as a live food, being practically always available. Tt is a fine fish food, given whole to the big fishes, chopped to the smaller ones, and shredded to  the very small ones or to fry. Special shredders may be purchased, resembling a pair of small gramophone records. The worm is placed between shredders, which are rubbed across each other with a brisk rotary motion, with worm puree as the result. If you are sensitive, the worms can be killed immediately before use by plunging them into hot water. Unfortunately, fishes seem to prefer them uncooked. Earthworms may be stored in leaf mold or in urban shrub boxes or window boxes, and they may be coaxed from the lawn by pouring a solution of potassium permanganate at a strength of about 1/4 grain per gallon onto the surface. They emerge in a few minutes. Avoid the dung worm, which is yellow and smelly and not good for fishes.

INSECT  LARVAE

Insect larvae are another fine live food. Those of various species of mosquitos and gnats are the easiest to collect in the right circumstances and may be netted in thousands in warm weather from stagnant water. They can be purposely cultivated by leaving suitable receptacles in the garden, but it is important to avoid increasing the adult mosquito population by doing this. For such collecting, it is important to have smelly, stagnant, dirty water. Clean water offers little food and does not attract the female mosquito. Decaying leaves or even meat will attract her.

The female lays egg rafts, small sooty-looking floating masses of 200 to 300 eggs, which hatch out into a swarm of minute "wrigglers." Typical species develop through the next 8 or 9 days and then hatch, offering a nice range of sizes of fish food. The larvae grow steadily and molt several times, finally turning into comma-shaped pupae, which soon hatch into adults. The larvae and pupae are air-breathers and so may be fed freely to the fishes without fear of crowding them out, although there is the possibility of their hatching into adults if given in excess.

When collecting larvae or pupae, it is best to catch them as cleanly as possible with a fine net and then, if necessary, to sort them for size by letting them wriggle down through a sieve or series of sieves made from various meshes of wire screening. If they are stored in a refrigerator, they keep longer without   metamorphosis and also keep sweeter. It is advisable to wash catches thoroughly and to feed the bigger ones only to fishes large enough to eat any unwanted young predators as well. Care must of course be taken to exclude any sizable
insect larvae, such as those of the dragonfly, likely to escape being eaten and to grow to dangerous proportions.

Chironomus larvae (bloodworms) are rather similar but are bloodred. Their parents are also gnats. They tend to stay down more than other gnat or  mosquito larvae and must be separated from mud after collection. This is best done by sieving, as with the others, choosing a mesh so that the mud escapes and the larvae are retained. Alternatively, they may be siphoned from jars, leaving most or all of the mud behind. After shaking the mud with contained larvae, it is allowed to settle, and the larvae are left behind for a short period as the mud falls down.

Chaoborus larvae (glassworms) are like bloodless Chironomu larvae, but they are found in cold weather and swim freely in the water. Sometimes they may be collected in quantity, and they keep well in crowded conditions. (Note that the terms "bloodworms" or "glassworms" are misnomers—the creatures are insect larvae.)

Maggots of various types are readily taken by the larger fishes. Their culture is not usually a welcome proposition, but in localities where garbage accumulates undisturbed a large number may sometimes be collected. Maggots are not suitable for chopping up. Other insect larvae are rarely collected in sufficient quantities to matter, but a mixed bag of the harder shelled types—those of water boatmen, for instance—are welcomed by large fishes like the cichlids and most anabantids.

CRUSTACEANS

The Crustacea provide many popular live foods, the chief of which is Daphnia pulex, the water flea. These small crustaceans are about the size of fleas and appear in warm, but not hot, weather, in stagnant pools. They may be almost colorless, green, or red, depending on the variety and also on their food. The red ones have hemoglobin, the same blood pigment we have.

When really plentiful, Daphnia occurs in large clouds and may be netted out in thick clumps, so thick that an improperly shaped net will ball them up together and injure them. The right net is fairly shallow  and does not come to a point but is rounded in section. The fleas will suffocate if not given fair room during transportation, and they should also be kept cool.

For some reason, Daphnia is regarded by many as the food par excellence. It is not actually very good food value, as it has a high water content and a hard, tough shell, and fishes fed exclusively on it do not thrive as a rule. It should be used in moderation for most tropical fishes, but it may be fed more liberally (when available!) to goldfish. It is available in dried form but is rather expensive this way, except for the fact that the dried eggs in the bodies of the females will often hatch out and can be used to start a live Daphnia culture. These are the winter eggs, which normally last over winter and hatch out the following spring.

The artificial cultivation of Daphnia is possible on quite a big scale, if large pools are available, and on a worth-while scale even in tubs or old tanks. The crustaceans normally live on unicellular algae and other organisms, and these must be supplied in bulk. They are cultured by enriching the water in the pool or tub with decaying vegetable matter or manure. Sheep manure is said to be best. An appropriate pool would be, say, 5X10 feet in area and 2 feet deep. After it is liberally seeded with refuse, the Daphniae are introduced and should
breed well. Such a pool might yield enough Daphnia to feed several hundred small fishes two or three times a week, but don't expect too much. Indoors, such procedures are smelly, and yeast or wheat flour may be used as the source of nourishment instead. If kept well aerated, these concoctions have little or no smell.

Moina, Cyclops, and Diaptomus and other less important Crustacea are found in the same fashion as Daphnia and can also be cultivated. They are not usually so abundant, nor are they as palatable to all fishes, but they are small and easily cultivated, and growing fry welcome them. Cyclops, unfortunately, seems to feed on the unhatched eggs of tropicals and should be excluded from breeding tanks at the initial stage.

Gammarus pulex and Asellus aquaticus are two common, shrimp like large  crustaceans. They are both 1/2 to 3/4inch in length, and both can be cultured in conditions similar to those for Daphnia. They are caught in the roots of border plants and rushes and often occur in streams. They are eagerly taken by the larger fishes, and their younger stages are eaten by smaller species. They have  also the advantage that they survive for an appreciable period in salt water and so may be fed to marine fishes. Uneaten specimens—and it is surprising how long
Gammarus, in particular, sometimes manages to escape—are excellent scavengers.  Another shrimp of the fresh-water variety is Hyallela knickerbockerii, which is also easy to raise and has the advantage over Gammarus and Asellus that it will stand tropical heat for breeding.

 

BRINE  SHRIMP

The brine shrimp, Anemia salina (or salens), is also a crustacean, but it merits a heading to itself. It is a live food of growing importance, in more senses of the word than one, as without it thousands of young fishes would never reach maturity. The genus Artemia is composed of small shrimps which live in very salt water, such as the Great Salt Lake in Utah, and whose eggs can withstand drying up completely for many years. Hence it is very important, for these eggs are now collected commercially and made available to aquarists all over the world. They can be stored for over a decade if necessary, as long as they are kept dry and at an even temperature. More remarkable still, they can be  dried out again, even after they have become moist, and they still will retain their hatching capacity.

The eggs look like a fine brown powder and are very minute. About the smallest pinch you can take contains several hundred, and it is customary to hatch many thousands at a time. They are not used until they are hatched—it is the living young shrimp that are of importance in feeding baby fishes, and even adults of the smaller species. For hatching, use shallow dishes or pans that hold a pint or more of water, according to need.

The following directions are based on the recommendations of the San Francisco Aquarium Society, Inc., producers of brine shrimp eggs: The eggs hatch only in salt water, but oddly enough they hatch more quickly and more evenly in weaker salt water than is needed by the adults. They thrive beautifully in sea water, although the adults do not. Thus, for hatching, use 6 heaped tablespoons of salt to a gallon of tap water (approximately 6 ounces to the gallon, or a 31/2% salt solution). The eggs will float on the surface and should be sprinkled onto the water and left there, using not more than 1 teaspoon of eggs per 2 gallons of water in shallow vessels. If a deeper vessel, such as an aquarium, is used, employ aeration. The eggs will hatch in about a day at temperatures of over 70°F., but they will take a week or more at less than 65°F. Even at 70°F. some of the eggs will take a couple of days to hatch out. If more eggs than recommended above are used, relatively fewer will hatch.

The empty egg shells will continue to float if undisturbed, whereas the shrimp swim in the body of the water with a jerky motion. They also collect in the lightest part of the vessel and will congregate so thickly that they will suffocate in a spot that is really bright in contrast to the rest. They may be siphoned off, free of egg shells if the last few teaspoons of water are left behind, and drained on an old handkerchief or other cloth. They should then be rinsed in fresh water, to avoid introducing gradual doses of unwanted salt into the fresh-water tank, and fed with an eye dropper or by rinsing the cloth in the tank. The hatching water may be used repeatedly as many as six times, replacing evaporated water with fresh tap water, as the salt doesn't evaporate.

Brine shrimp grow to about 1/2 inch in length and are a meaty meal at that stage. They need a different brine from that used in hatching, so that newly hatched shrimp  should be transferred within a day or two to a brine made by taking a breakfast cup (10 to 12 ounces) of salt, 2 heaped tablespoons (2 ounces) of Epsom salts, and 1 table-spoon of baking soda to a gallon of tap water. This brine is about twice the strength of sea water and much more alkaline.

The young shrimp (nauplii) feed naturally on algae, etc., but baker's yeast may be substituted—about 1/4 teaspoon per gallon, well stirred up. Into a gallon of brine plus yeast, preferably in a shallow tub or tray, put just a few shrimp—not more than a few hundred, unless you intend to use them only partially grown, in which case thousands can be reared. Feed yeast again when the brine clears, which may be in a day or a week, according to temperature and the number of shrimp. Cover to prevent too much evaporation. The shrimp reach maturity in about 6 weeks, sooner if kept really warm, and they will feed on yeast throughout the period and reproduce readily. Thus, the culture, if undisturbed, will soon contain both young and older shrimps, but do not expect it to yield an indefinite supply—you will still need to  buy more eggs. Siphon off and wash the adults as you would the young before using them.

TUBIFICID WORMS

The mud worm or sludge worm, Tubifex rivulorum and other similar Tubifex or Limnodrilus species, are excellent food, but they are found in very questionable circumstances and should be carefully washed before use.

The Tubifex worms absorb waste material from slow-moving polluted streams, being rarely found in quantity in stagnant water. They are reddish in color and vary with species from threadlike creatures 1 or 2 inches long to really solid worms 3 to 4 inches in length. They live at the bottom or sides of streams and wave their tails in the water, retiring promptly into a tube in the mud when disturbed. They may establish themselves in an aquarium and be hard to eliminate (Cory dor as do this), and whether they are regarded as an acquisition or a nuisance depends on the aquarist.

Collecting Tubifex is usually a filthy task. If they are present in worth-while amounts they will be seen as a reddish wriggling carpet or patches, which jerk into the mud when a shadow or footfall disturbs them. Dig well under the mud where a patch was seen—or if you are lucky the patch may be so thick that even when retracted it is still visible—and put mud and all into a large bucket. When you have a bucket nearly full, leave it until lack of oxygen forces the worms to collect at the surface, when they may be removed with still some mud adhering to them. If they must be left for long, run a gentle drip of water into the bucket and if possible cover with a layer of sand, through which they will emerge fairly clean. Otherwise they will die and be useless. Most of the worms can be removed within a day or two. Wash the worms well under a fairly brisk stream of water to remove much of the residual mud. They will aggregate into balls and may be stored for a long time, even a month, if they are placed in large vessels of water under a constant drip from a tap or hose, with a suitable overflow arrangement. They also store well in an ice chest or refrigerator, and clear of mud they do not smell until they start to die. Stored masses should occasionally be stirred up and washed more briskly, to remove the dead and the feces, and they should not be fed to fishes for at least the first day.

Tubifex may be cultivated in slowly fed muddy streams, artificially made in the garden, but it is not an easy task and the arrangement is unsightly. They will live on stale bread, broken up and thrust into the mud, but they really thrive only in filthier conditions than the most ardent fan is likely to tolerate. A word of warning—do not wash and prepare your Tubifex in the kitchen sink or even at an adjacent drain which communicates with it. They have a remarkable facility for collecting in U-bends, where they feed on waste from the domestic washing-up, etc., and eventually cause blockage.

WHITE WORMS

White worms (Enchytrae) are relatives of Tubijex and of the earthworms. They are small worms about an inch in length, commonly found in cool, moist surroundings where there is plenty of humus or other decaying matter for them to use as food. The underside of dustbins when on soil is a favorite spot; but the worms are  practically never collected from such sites now, as they may be purchased from dealers to start a culture. The common variety is Enchytraeus albidus.

There are several methods for cultivating them. They may be cultured on a fair scale in wooden boxes of rich soil, with added humus and oatmeal. These are stored in cool cellars, and more oatmeal, mashed potatoes, cheese, bread, and milk or a variety of other foods are placed on the soil or into small holes in it, at intervals of a few days. The box is tightly covered, preferably by a sheet of glass in contact with the top of the soil, mainly to exclude ants and other predators (even mice), but also to keep a damp state—not wet, just damp. When needed, the worms may be scraped off the glass or from the food pockets.

On a smaller scale, the worms may be cultured between milksoaked crusts of bread, stored in tightly covered tins or other vessels.It is advisable to boil the milk and to pour it on the crusts while hot, as this helps to sterilize them and to prevent early souring of the culture. This method nevertheless requires frequent sub-culturing, as the bread slices rapidly go foul and moldy.

There is usually little trouble in separating white worms from their food, but if necessary, place the mass of half-cleaned worms on a rather hot surface, and they will rapidly crawl to the top.

MIKRO WORMS

There is a group of minute Nematode worms of the genus Anguillula, the most familiar being the vinegar eel, A. aceti, and the paste eel, A. glutinis. Another A. silusiae, is found in soil, and it is assumed that this is the species usually called the mikro worm (or microworm). It was first cultivated by Swedish aquarists. It is a very small livebearing worm, at a maximum about 1/10 inch long, with young very much smaller. Therefore it is an important food for young fishes, and it is beginning to rival brine shrimp as it is considerably cheaper to culti-
vate in large amounts and the younger stages are smaller than newly hatched brine shrimp.

The mikro worm is easy to culture. This is best done in shallow vessels, with tight covers. In the base of each vessel is placed about a 1/4 -inch layer of any of the quick-cooking breakfast oatmeals or wheatmeals. The use of wheat germ is said to give superior results.

The meal is cooked just as for ordinary use, preferably with milk, but without salt. It is then inoculated with a little bakers' yeast and some mikro worms. Growth is rapid, and the worms form a seething mass in a few days. If small pieces of wood, water-soaked beforehand, are placed criss-cross over the meal so that the top ones are clear of it, the worms crawl up and collect free of cereal on the top pieces. If the sides of the vessel are roughened, as can be done with plastic containers, the worms will crawl up them and can be scraped off. It is not usually worth while to feed cultures once they have been established, but it is best to keep a series going so that worms are always ready for use. Each culture will last up to 2 weeks, and the worms thrive best in warm temperatures, up to 80°F.

Mikro worms withstand dessication, so that a dried-up culture can be restarted merely by wetting it. A new white worm, intermediate in size between the usual one and the mikro worm, has recently come into prominence. It was first cultivated by Mrs. Morten Grindal, a Swedish aquarist, whose name has become attached to the worm. It was isolated from ordinary white worm cultures, and it prefers more heat than the usual Enchytrae. It is at most % inch in length and slimmer in proportion than white worms.

Cultures are maintained as with white worms, except for a higher temperature—70°F. or a little more seems best. Growth is apparently very rapid. As yet, the exact identity of the newcomer does not seem to have been established.

INFUSORIA AND ALGAE

Microscopic pond life is legion, and much of it is suitable as food for fry. The word "infusoria" is so commonly used that it will be employed here, but it has lost any precise meaning except to denote anything very small in the way of pond animals, usually needing a microscope for recognition. The older German writers on aquatic matters were very fond of prescribing "pond infusoria" for the feeding of fry, with little hint of how hard it usually is to collect enough to be of any use. It is in any case much easier and safer to cultivate these organisms free of the unwanted pests and diseases which may be gathered in from the pond.

The rough-and-ready way—which usually produces quite satisfactory results—is to prepare a reasonably sterile medium and let it develop when exposed to the air. This will be only reasonably pleasant to the nose if aeration is supplied, and it also much improves the yield. A great variety of substances may form the base. The best is a rich vegetable infusion made by boiling almost anything from potato peelings to chopped lettuce leaves or banana skins for a few minutes and cooling. About a fistful per 10 gallons is right. If you wish to cultivate a specific organism, keep the boiled water covered and introduce the desired species, either from a purchased culture or from a few specimens carefully selected by means of a fine pipette from pond water or other source. The infusoria appear in force within a few days. A temperature of 60° to 70°F. is best, without too much light.

In a strong light, an excess of algae is likely to develop, and this may swamp out the more desirable animal life. Single-celled free-swimming algae are useful, however, and are the cause of "green" water. These help to feed some of the infusoria, but if present in excess they may suddenly die and foul the culture.

There is little point in listing even the commonest forms of minute life found in such cultures. Particular attention has centered on a single-celled animal, Paramecium, and its value as a fod, and on rotifers, multicellular but nevertheless small animals which are eaten by some fry as a next stage in the food cycle. These are only two of numerous common and, as far as we know, about equally valuable types. They or their eggs are capable of drying up and being carried in dust to suitable sites for further expansion. The success of a culture can be checked with a hand lens. Water taken from the lightest side of the vessel should swarm with life, visible as moving specks in a drop placed on a glass slide and looked at against a dark background. Although infusoria are small, the useful ones are not so small that they cannot be seen in this manner, and anything that is too small to be visible with a simple lens is unlikely to be of much food value.

The vegetable infusion may be replaced by chemicals, but if this is done the first organisms to thrive in the culture will necessarily be algae, followed by animal life later. A suitable solution resembles those used in hydroponics, the water culture of higher plants. The constituents could be: —

Potassium nitrate	4 grams
Sodium chloride	2 grams
Calcium sulphate	2 grams
Magnesium sulphate	2 grams
Calcium phosphate	2 grams

plus a trace of ferric chloride, in 1 gallon of water.

FRUIT  FLY

The vestigial wing mutation of Drosophila melanogaster, the fruit fly, is an offshoot of the genetic work done with this species, useful to aquarists because it cannot fly. It may be cultures in milk bottles with cotton wool plugs in the neck. The bottles are scalded out and sterilized (i.e., scalded and then dried)  and the cotton wool plugs are placed in position. About one over-ripe banana per bottle is skinned, mashed, and sieved, and to the result is added 2 1/2 ounces of water and 1/4 teaspoon of nutrient agar per banana. This is boiled over slow heat, with constant stirring, and when it is boiling 1/4 teaspoon of Turtox or Moldex is added per banana; either will prevent the growth of unwanted molds. When it has been added, stirring is continued for 3 minutes and then about 1 inch of the liquid is poured into each bottle, leaving the neck open for as little time as possible. A small fan of paper toweling, sterilized at the same time as the cotton wool, is also placed into each bottle, so that it reaches from the neck, below the plug, to the bottom. This is for the insects to crawl upon. Allow the bottles to cool, add a pinch of yeast, any variety, and a few flies. They will produce larvae in about a week and flies in about 2 weeks. They must be kept reasonably warm.

TADPOLES AND FRY

Newly hatched or half-grown tadpoles and fry of any fish are very good foods. Guppies, blue gouramis, and some of the barbs are particularly likely to overproduce, for the egg-layers should be spawned when ripe, even if the fry are unwanted. They should be grown to a suitable size on prepared food if necessary and then fed to the more precious varieties. By this means, powdered food can be transformed to live food when the latter is in short supply. Take care, however, that the tables are not turned, and that a rapidly growing, unconsumed gourami doesn't shoot ahead of its intended consumers and eat them instead.

Antibiotics

Results with various animals from pigs to fishes have shown that the addition to the food of small amounts of some of the new drugs known as antibiotics is sometimes beneficial. The animals gain weight more rapidly and are said to be in better condition generally. The most favored antibiotic is aureomycin, but penicillin and others are also used. It is not yet clear whether any undesired effects may show in breeding performance or resistance to diseases later on, but there is no obvious reason to think they should. For fishes it would seem as feasible to add the drugs directly to the water as to mix them with the food, but perhaps direct ingestion is preferable.

Feeding

As explained in the preceding chapter, the warmer the water, the better the appetite of fishes, up to about 80°F. Thus, goldfish need almost no feeding in the middle of winter and in normal cold weather should be fed only two or three times a week. In summer, however, twice daily is not too often. Tropicals are never so torpid as the coldwater varieties at the lower end of their temperature range but have in general poor appetites at temperatures below 70°F. At 75°F. they are good eaters and should be fed two to three times daily, and at 80°F. they are really hungry and will eat practically as often as they are fed. Even so, they will not starve if fed only once per day, particularly if fed on live food, some of which may escape and be consumed later. Too much live food must not be given, however, or it may compete successfully for oxygen. The feeding of prepared food requires careful handling. The tendency of the beginner is to give far too much. This is curious, as the true tyro often cherishes the belief that fishes live on microorganisms in the water and do not need feeding at all. From that, he seems to swing to the other extreme in action. It is therefore more important than almost anything else in fish keeping that the following rule be strictly adhered to at all times. It is a rule given by Innes:

Feed only enough prepared food at one time so that practically ALL of it is consumed within 5 minutes. Then siphon off any that remains.

Only after long experience can an aquarist walk round his tanks and throw in the right amount of dry food without looking to see the result. Watch the fishes each time you feed them, see them eat the food, and see that they are well and alert and eating normally. Feed dried food fairly slowly, and give it time to swell up with water inside the fishes before they stuff themselves with too much. Some aquarists soak the food first, but the fishes do not usually eat it so readily when this is done. Feed little and often rather than the reverse.

As a rough guide, 1 ounce of prepared food such as a wheat germ and shrimp mixture will last 100 average-sized tropical aquarium fishes of mixed varieties at 75°F. for about 2 weeks with no other feeding.

This is about 10 milligrams per fish per feeding, twice daily, which doesn't seem much but is enough. As long as they are well fed normally, adult tropical fishes can be starved without trouble for several days. Even a couple of weeks is feasible, as long as the temperature is about 70°F. Cold-water fishes can take starvation even more easily as long as they too are reasonably cool—say below 60°F. Longer periods may be survived, but the tropicals at least will be pretty emaciated and may never breed again. The importance of this fact is that, during a normal vacation of not more than two weeks, it is possible to forget the fishes (not, of course, young fry). This may be preferable to getting someone else to feed them, unless he also is an aquarium keeper. Others nearly always manage to do something disastrous, the most common being gross over-
feeding and pollution. If a non-fancier must be asked to undertake the task, it is vitally necessary to give him a few lessons or at least to make up separate packages of food, one per feeding, with strict instructions not to supplement them with anything else whatever. The latter method is perhaps the safer, with or without additional lessons! The remarkable thing is that a substitute can watch a tank go foul and cloudy, see fishes gasping at the surface, take out the dead ones, and still go on overfeeding.

There have been various designs for automatic feeding apparatus during the absence of the owner, but none has come into general use. The only food which can be given in mild excess to tide the fishes over a projected lean period is mosquito larvae. These do not consume dissolved oxygen to any appreciable extent and will survive if uneaten for several days on the average before turning into pupae and then adults. A tight cover over the tank will prevent the escape of any that manage to reach that stage.

Only in a sparsely populated tank would it be worth risking the addition of substantial amounts of other live food, such as Tubifex or white worms.

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