Feeding and Rearing the Fry

Two quite recent fish foods have revolutionized the rearing of fry. These are mikro worms and brine shrimp. Before they were available or had been popularized, raising a tank of two or three hundred young fishes was quite a task, particularly if the fry were very small at first and required an extensive period of small, live food. Even now, older methods die hard, and many aquarists condemn themselves to several weeks of infusoria feeding even with fry which are perfectly capable of eating either of these excellent live foods from the start. Or, worse still, they attempt the job with powdered dry food, egg yolk, or other such difficult live food substitute.

Not all fry can be started on mikro worms or brine shrimp, and some have to be supplied with smaller food for a few days, but a surprising number can eat them from the start, especially the young of the mikro worm, though the parents may be too big. Thus, newly hatched giant danios (Danio malabaricus), zebra danios {firachydani rerio), glowlight tetras (Hyphessobry con gracilis), head and tail light fish (Hemigrammus ocellifer) and most of the barbs, to cite only a few examples, can take brine shrimp as soon as they are free-swimming. It is not the size of the young that counts as much as their mouth capacity or even their willingness to accept a particular food. With any given species, it is easy to see whether they are eating brine shrimp because their bellies show a red color even when only one or two have been eaten. It may be observed that not all the fry are taking them, perhaps only the largest, and it must then be decided whether to arrange for supplementary feeding of the unlucky ones, or to let them starve and raise only the biggest starters. It may be added that either of these newer live foods appears to be a complete and satisfactory food on its own. There is no need to worry about varying the fishes' diet in the early stages if these foods are given.

In what follows, therefore, it is to be understood that, if one or both of these foods are available (and they are easy to get), they will normally be used as soon as possible. Discussion of alternative feeding methods is included because these are sometimes needed before the fry can take bigger food and may be needed as emergency substitutes at any time.

Foods and Food Sizes

Grade 1, the smallest foods, include one-celled algae, baker's yeast, some infusoria, infusions of hard-boiled egg yolk thoroughly shaken in water, or very finely ground dry shrimp or other dry food. Some particles of dry food will always be too big, but many can be taken by even the smallest fry.

The unicellular algae are supplied as green water, which will also contain infusoria. Fry such as those of the dwarf gourami (Colisa Mia) and the Siamese fighter (Betta splendens) need a start with green water for just a day or two. Naturally, it is best to spawn the parents in green water if this is possible, but such a maneuver is sometimes undesirable because of possible difficulties in catching the female.

Yeast must be used with discretion, just a drop or two of a thick suspension being enough, and it has the advantage of being a live food. The egg suspension is prepared by shaking a small nugget of hardboiled egg yolk in a bottle with 2 or 3 ounces of water until a cloudy suspension results. Very fine dry food is best prepared in a pepper mill or by grinding it between smooth, flat surfaces for a considerable time. Fry will often only take moving food; therefore a very gentle aeration current helps, not enough to exhaust the fry but sufficient to keep the food gently moving.

Grade 2, the next size of food, is often small enough for starting. These foods are mikro worms, newly hatched brine shrimp, larger infusoria, small rotifers, finely shredded earthworms, or finely ground dry food. Again, gentle aeration helps with the inert foods and with mikro worms, which do not always swim up into the water very much. When brine shrimp are given, a light placed directly over the tank attracts the shrimp upwards and keeps them swimming in the water. Otherwise, they may collect at the bottom of the tank, remain
uneaten, die, and foul the tank.

When Grade 2 dry or shredded food is used, the time has come to introduce small snails to consume unwanted residues.

Grade 3 is suitable for all fry after a few weeks, and for large newly hatched fry or newly born livebearer young. It consists of small sifted Daphnia, "Grindal" worms, Cyclops, newly hatched mosquito larvae, large rotifers, chopped white worms and small granule dry food. Although foods of Grade 2 are still quite suitable for older fry or large newly hatched fry, they can take Grade 3.

Grade 4 is suitable for half-grown fry (%_ to 1 inch in size). These may be given Daphnia, mosquito wrigglers, small chopped earthworms, young unwanted fry of other species, and medium sizes of dry food. Even these fishes may be fed on mikro worms or newly hatched brine shrimp, on which they thrive as long as  they are given enough of it. Brine shrimp may with advantage be grown larger for a few days, at least, by feeding them a little yeast, and in the process, they will increase severalfold in food value per pinch of eggs originally hatched.

Infusorial Feeding Methods

The need for a continuous supply of live food or of moving suspended food particles in the early days of the life of the fry may be supplied by drip feeding. Many successful breeders never use this method, and it is certainly not necessary, but perhaps an equal number feel happier if they do supply it. Since one purpose of keeping fishes is to enjoy feeding and caring for them as well as looking at them, why not do it if you like to?

When a spawning is planned, an infusorial culture should be on the way, in case it is needed. But if it is not produced, use an egg or yeast suspension instead. To feed by drip, it is necessary to siphon the culture very slowly over into the tank. It is not usually necessary to supply a drain for overflow, but a gadget for the purpose will also be described.

The main difficulty in drip feeding is usually to get a slow enough drip, but this is achieved very easily by means of the device illustrated. A 1/16 -inch (internal diameter) glass tube is bent as shown and inserted into a cork or other float. This diameter tubing fills itself by capillary action and will drip at 1 drop per minute (3 cubic centimeters per hour) or faster, as long as the end of the tubing is bent upwards as shown. If it faces downwards, the minimum speed will be about 40 drops per minute, and that is too fast for most cultures. The rate is controlled by raising or lowering the tube in the float. Very slow drip rates are best prevented from stopping because of surface tension effects by slipping a piece of tubular tape, wick, or shoelace over the dripping end. A % 6 -inch siphon is self-starting and can be used in the tank as an overflow drip of similar design.

An alternative drip feed is a wick or piece of cloth, but this may filter off too much of the culture, leaving behind a rich medium and delivering a very  thin one. Actively feeding fry will eat continuously at the rate of several small infusoria per minute; therefore, a tank of, say, 200 fry needs some 60,000 organisms per hour. A rich culture may supply 100 to 200 very small organisms per drop; hence a drip rate of about 300 per hour or 5 per minute might be right, but only experience and rough counting of both culture and fry numbers can tell. Fry feeding on pure Paramecium cultures need fewer of this
larger infusorian.

The number of infusoria needed per day can be dumped into the tank in two or more doses and will not overpopulate the tank while being eaten, as long as the fry are not extremely crowded. That is why drip feeding is rarely a  must, but the dumping has to be done with reasonable foresight and careful checks on the condition of the tank. Watch the fry, see that they are eating, and estimate, even if only roughly, the proper amount of culture to feed. Quite wide margins are tolerated and only normal care has to be taken, but some care
is essential. Remember that not very much is needed at the start, but the rate at which the fry require food is always increasing as they grow and larger amounts must be supplied.

From the start, therefore, it is perfectly feasible to raise fry with 2 feeds per day, morning and evening (but give them light to feed by). Occasionally a spawning may be lost because of a foul tank or unnoticed underfeeding, but the numbers of spawnings that can be coped with by this simple scheme more than make up for this mishap. Anyway, spawnings are lost more frequently by older methods. There are certain advantages, too, in the infrequent feeding technique. For example, when a mass of food is given all at once, the greediest fishes cannot eat it all and must temporarily leave some for the weaker ones.

This means that the weaker ones get some food, whereas with drip feeding they may starve if the stronger and greedier fry sit under the drip and grab it all. This does happen, and it is probably another reason why drip feeding is not always very successful.

Later Feeding

If an infusorial, green water, or other fine-food start has been necessary, try after a couple of days to substitute a Grade 2 food. Give them some and watch what happens with a hand lens. See if the food is taken, and try to estimate if all the fry are taking it. If not, give both foods together for a day or two, and so make the change-over gradually. Do exactly the same when attempting to change from any food to another food of larger size, and do not starve your smaller fishes. They will not turn out to be runts unless you force them to. By this method, most if not all of the fry can be brought along as a nice even batch. The exception is goldfish, among which a spawning may be so variable that all sorts of fry sizes and quality are encountered despite the most careful feeding. But with tropicals, which breed true, 10% of runts is as much as should be expected. The rest will vary in size a bit but should not show the enormous variation so often seen in which the largest fry finally eat the smallest and so Growth of the fish in the preceding figure from immediately  after hatching to 1 and 2 weeks. Changes during the first week occur with practically no food intake.

even things up a bit. This is due to inadequate or inappropriate feeding, or both, and can be avoided. As the fry grow, even if they have been raised entirely on live food for the first few weeks, it is quite in order to start substituting a proportion of dry food. Keep to live food all the time if you can, but do not starve the fishes by trying to economize in a 100% live-food campaign. As with  full-grown fishes, fry after the first few weeks do well on about 50% live food and quite well on only 25% or 30% if really necessary.

Although goldfish fry can tolerate lower temperatures, they do better if kept at 70° to 75°F. during the early growing period but do not thrive so well much above 75°F. Their feed can be the same as outlined above.

Space Requirements and Culling

Young fry can stand much crowding. Even when 1/2 inch in length, most species can be packed some 30 or 40 to the gallon. An outstanding exception is the goldfish, in which fry need good space after the first few weeks for adequate growth and must be sorted out fairly early. The fry of nearly all tropicals can be kept in the small 3- to 5-gallon breeding tank advocated for the first 6 weeks unless there is a spawning, say, of over 250 per tank. In such a case they will do better if given more room after the first 4 weeks. Goldfish fry will stand equal crowding at first, but after 2 to 3 weeks they should be
much more liberally provided with space, so that by the time they are 6 to 8 weeks old there should be only about 5 to 10 per gallon, and progressively fewer as they grow up.

In the goldfish, this process will be accompanied in the usual course of events by quite severe culling, so that the capacity of the aquarium is not so badly strained as it might seem at first sight. Culling can start as soon as you can see body and finnage shapes and sizes. Culling for color is impossible until much later. With all types of goldfish, good shape, finnage, and color are attained by only a very small number—less than 1% is usual. With the fancy types, vast numbers of "throwbacks" occur, some of which are worth keeping as good examples of different classes, but many are useless. The genetics of gold- fish are complex, no doubt made so in part by the reluctance of breeders to inbreed consistently and so help to clean stocks up.

Thus, with the goldfish, culling can be severe. It all depends on your standards and on how many relatively inferior fish you wish to keep for disposal or pond stocking. Few will be worth keeping for further breeding. With tropicals, which throw far fewer abnormal or undesirable forms, it is usually the aim to keep most of the spawning, rejecting only a few runts or badly shaped individuals during the first weeks, and later selecting those which grow best and have the  icest general appearance for breeding. There are few standards for tropicals
as compared with goldfish, and it is much more of a personal affair as to which type of fish you like best for breeding, the full-bodied or the slimmer fish, the giant or the smaller-sized, perhaps more brilliant adult. Variation is in any case much less.

When a batch of tropicals has reached a size at which they can be safely moved from the premises, which occurs after 6 to 10 weeks, depending on their diet, numbers, growing space provided, and temperature at which they have been kept, a number may be kept for future breeding. These, of which at least a dozen should be selected, will be given the best of food and conditions and may be ready for breeding within another few weeks, or perhaps not for a year, according to species. It is usual to select the best of the largest fishes, if there is much size difference, for it is a curious trait of fish fanciers that they confine their attentions to small species that are easy to handle and are not too bulky for life in home aquaria and then do their best to grow them as large as possible. This cannot happen with goldfish, since the biggest ones and the fastest growers are the throwbacks. Big fish are not necessarily the healthiest, although they are unlikely to be unhealthy, nor are they necessarily of the best shape or color. Yet, selection for size is likely to be of more influence than any other single
factor, and its effect must be kept in careful check by the thoughtful breeder. Do not pick runts, but do not just pick the whoppers, even if they look good. Medium-sized fishes may be just as healthy or even the healthiest, resembling ourselves in that regard. Think of the effect on the human race if no one under 6 feet were allowed to breed and no attention were paid to other desirable characters.

Ridding of Pests

If the brood tank has been adequately disinfected, pests will have been eradicated at the start. However, they may get in or be introduced during rearing, but they will usually be at a disadvantage compared with the fry, which will often eat them. Young snails at the fry-raising stage are a help, not a pest, and should be encouraged. The same is true of planaria and many other organisms which were unwanted earlier. However, a few undesirables are liable to crop up, the worst of which is Hydra. Hydra feeds on small organisms and is very likely to appear in swarms when these abound, as in the brood tank.

If present early, it is a menace to small fry; later it may compete with them for food. In nearly all cases Hydra may be eliminated in the presence of fry by adding ammonium nitrite or sulphate to the water. The appropriate quantity is 5 grains per gallon (90 milligrams per liter, or 1 part in 11,000 approximately), added already dissolved in a little water, and well stirred up. The temperature is then raised to 5° to 10°F. if possible. It is essential not to allow the ammonium salt solution to form a layer at the bottom, which will kill the fry. The treatment is best given after feeding the Hydra well. They do not disappear dramatically but fade away over the course of the next few days. A second treatment may be given if necessary, but if, for some reason, that is no good, further treatments should not be applied. Blue-green algal or bacterial film sometimes settles on the surface of newly set aquaria and on breeding tanks also.

A piece of newspaper drawn across the surface is about the best cleaning agent  in this and similar conditions. The scum adheres to the paper and is mostly removed. Addition of healthy filamentous green algae to the tank often holds other types and even bacteria in check, and it is a fine environment for young fry, as it is a very good oxygenator and provides food in the form of the spores and the microorganisms it harbors.