Food for aquarium fish

When choosing compatible fish species for a general aquarium, one should take into account their natural eating habits. Fish requiring a special diet or exhibiting unusual behavior during feeding are sometimes best kept in a species aquarium (that is, in an aquarium where only one species of fish is present), where everything can be tailored specifically for their needs. It is not advisable to ignore these special needs or to expect that the fish of this species themselves will adapt to what they are offered. Most likely, such ignoring of their features will lead to the appearance of health problems or even to the death of pets.

Different food for different fish

It is extremely important to ensure that all the inhabitants of the aquarium receive enough food. Moreover, for the fish of each species, it is necessary to provide the appropriate type of food. There is no point in offering lettuce leaves to obviously predatory fish or large pieces of fish meat to herbivore. “Food incompatibility” can be associated with eating behavior (for example, many predators do not perceive stationary food as edible), as well as with differences in the digestive system: in particular, the intestines of herbivorous fish are not adapted to digest large pieces of food, and the intestines of carnivores cannot absorb plant matter.

These considerations are especially important for the general aquarium, as it contains fish of different species, differing from each other both in terms of food requirements and behavior during feeding. For example, bottom catfish and loaches may well remain hungry at all, since fish that swim in the middle layers of water or near its surface is usually the first to grab food. There are types of food that have the ability to quickly sink – pellets, tablets, and plates – they are designed specifically for bottom fish. However, you cannot use only such food if there are fish in the aquarium where fish exclusively on the surface of the water.

Food nutritional value

Crucial to the overall well-being of fish is the nutritional value of the diet. Fishes that regularly eat poorly may experience slower growth. In severe cases, they may develop symptoms of deficiency of essential elements such as skin and eye diseases. A healthy diet is also necessary to maintain fish’s natural immunity to infections.

In an aquarium, it is almost impossible to provide fish with a full range of natural food. To do this, it would be necessary to supply them with tropical aquatic invertebrate animals, plants, algae, etc., and in order to provide the nutrition necessary specifically for fish of this particular species, all this would have to be collected in the natural environment where these fish live. Instead, it’s better to look for more affordable sources of fish feed.

Fortunately, most species of aquarium fish, especially those raised on fish farms, are willing to take artificial feeds. The proportion of fish caught in the wild is relatively small, and it may take some time to wean these fish from natural food and accustom to an artificial diet. It so happens that the fish refuses to take any food except live. Some fish species, mainly fish-eaters, such as the viviparous pike Belonesox belizanus, are known for being very difficult to accustom to non-living food. Therefore, before deciding to keep such fish in his aquarium, the aquarist must be sure that he can provide them with suitable live prey all year round.

Commercially available aquarium fish food

When a hobby such as an aquarium farming had just begun, aquarium fish were usually caught or prepared by the aquarists themselves. Popular types of food were food leftovers from the kitchen, such as beef heart, hard-boiled egg yolk, vegetables, as well as live food such as earthworms and Tubifex tubule. Many of these types of feed are still popular today. Great popularity was enjoyed by such a form of feed as ant “eggs”. They could be bought in stores in dried and packaged form. In fact, these so-called eggs were nothing more than dried cocoons of larvae with no nutritional value.
Nowadays, the trading network has a wide variety of high-quality dry, frozen, and live food for tropical aquarium fish. Examples of these feeds are given below.

Dry food – cereals, granules, and tablets

The most popular food for tropical fish is so-called dry food. Flakes are especially well known – they are ideal for many small and medium-sized fish – as well as pellets and tablets. The last two types of food are of different sizes and are intended for fish of different sizes. They are characterized by low moisture content (less than 4%), which helps prevent their damage due to the activity of microorganisms, such as mold and bacteria. In addition, the dry condition of these feeds guarantees a long shelf life. There is one more advantage – when feeding from them there is not as much dirt as from dough-like food.

Fortunately, most aquatic fish on the market in captivity easily adapt to these “unnatural” dry foods. For many generations of popular aquarium fish, such as the Poecilia reticulata guppy and the Pterophyllum scalare, they have been raised in fish breeders and multiply by feeding on a mixture of dry and live food.
When buying dry food, it is very important to choose a quality product, and not a substitute that has insufficient nutritional value. The composition of high-quality dry feed is selected in accordance with the nutritional needs of a wide variety of fish.

It is suitable for feeding most tropical fish found in a common aquarium. In addition, there are specialized products on the market whose composition is specially selected for fish of specific species or groups. Examples include food for cichlids, catfish, discus, herbivorous and carnivorous fish, as well as food in the form of sinking tablets or plates intended for bottom fish. So, some types of dry food are suitable for a certain type of food or for fish of certain species.

At the same time, we must not forget that the order catfish(Siluriformes) and the family Cichlids(Cichlidae) include fish that are significantly different from each other in terms of nutrition so that there is no universal food that is suitable for everyone. It should be remembered that some cichlids often suffer from indigestion if fed with inappropriate food. Sinking food can also not be universal and satisfy the most diverse nutritional requirements that are characteristic of bottom catfish and loaches, as there are both carnivorous and herbivorous fish among the representatives of these groups.
There are other specialized dry foods, such as those that enhance the color of fish, as well as high protein foods that are necessary for rearing young fish.

aquarium fish food


In addition to dry food in the form of flakes and granules, organisms dried at low temperatures are available, which serve as live food for fish, such as bloodworms and Tubifex tubule. With this method of preparing feed, excess moisture is removed from them, and this does not have a special effect on the content of nutrients in them.

Frozen food

Although many species of fish can eat exclusively dry food, a varied diet will benefit them. Therefore, from time to time it is worth giving them fresh or frozen food. The latter is especially popular among many aquarists. Such food must be stored in the freezer or in the freezer compartment of the refrigerator. An industrial freezing process, sometimes involving gamma rays, kills most pathogens that infect fish. Therefore, giving fish food subjected to gamma irradiation and freezing is much safer than feeding the same food live.

Some types of food for aquarium fish, listed below in the “live food” section, are also sold frozen.
If you purchased frozen food for your pets, first thaw it or let it thaw quickly in a net under a stream of cold water from a tap and only then feed it to the fish. If this is not done, the fish’s stomach may become excessively cold. In addition, ice crystals contained in frozen food can pierce the intestinal wall of small fish. The liquid contents should be drained away – the fish is still not able to absorb it, so the organic substances contained in it will only pollute the aquarium in vain.

Live food

If you want to choose 7 types of live food for aquarium click this link!

Live food, especially aquatic invertebrate animals, form a very important component of the diet of many wild fish. For example, fish that feed on the surface of the water can eat large amounts of aquatic and terrestrial insects. Insects fall onto the surface of the water and are captured by a surface film. Other fish species, such as bottom fish, feed on the ground with larvae of aquatic insects, crustaceans, and worms living in bottom sediments. As noted above, supplying aquarium fish with invertebrates from their natural habitat is an impossible task for most aquarists. However, in many cases, it is still possible to provide them with the prey of approximately the same type, for example, mosquito and small crustacean larvae.

Live feeds have many benefits. Most of them have high nutritional value, and the main vitamins and other nutrients contained in them remain intact and will not be destroyed during processing, as happens during the preparation of some dry food.

Fish have natural nutritional instincts (even bred in fish farms). Therefore, they usually react more lively to moving prey than to stationary food. In fact, fry of many species and even some adult fish generally recognize only moving food as edible, so if you give them only dry and frozen food, they can reach starvation. The fish food industry is innovating, trying to somehow “revitalize” dry feed. To do this, they include special chemicals that emit gas bubbles and set in motion the food in the water. However, so far these attempts have been unsuccessful.

The main negative aspect of feeding fish with live food is the risk of introducing diseases and parasites. Pathogenic microorganisms (bacteria, viruses), as well as parasites, can be present in the viscera or body tissues of organisms used as live food. In addition, the natural water in which such live food is collected can in itself become a source of disease or parasites. Freshwater crustaceans, such as Cyclops, may contain larvae of parasitic worms (helminths), and the tubule Tubifex is known for being a carrier of pathogenic viruses, bacteria, and even some protozoan parasites.

Live food, intensively grown in open systems where there are no fish, are much less likely to carry such diseases. However, aquarists do not have reliable means to distinguish specially grown live food from the same food collected in some local pond or stream. Special treatment of water or purification of live food can save them from some parasites and pathogenic microorganisms, but these procedures cannot be completely relied on since they cannot destroy the causative agents of all possible diseases found in food. Thus, the risk of introducing diseases into the aquarium along with living food is very significant, and the aquarist should always remember this.

Crustaceans from salt water bodies

Artemia, which has just emerged from eggs (nauplii), are commonly used as food for fry (see the link). In recent years, live adult brine shrimp are sold at some retail outlets for feeding large fish. True, they are quite expensive, but it is excellent food. Before feeding brine shrimp to fish, be sure to rinse them with tap water so that salt does not accumulate in the aquarium.

Insect larvae

Bloodworms (red mosquito larvae) are larvae of mosquitoes. They are usually found in detritus clusters at the bottom of ponds or other bodies of water with standing or slowly flowing water, the bottom of which is covered with silt or other organic matter, or is densely overgrown with algae (mud). These are blood-red larvae of about 1-2 cm in size. Sometimes they can be purchased at pet stores, but we do not recommend this, as some sources of their production are heavily contaminated, and an infected bloodworm can become a breeding ground for pathogenic microorganisms. A person who is completely dedicated to such a hobby as aquarium keeping can collect bloodworms in safe places, but for this, he will have to choose individual larvae from detritus with tweezers. Therefore, the easiest and safest option is to buy a frozen product that has been disinfected.

Corethra(white mosquito larvae) or glassworm are the transparent larvae of the necro-sucking mosquitoes Chaoborus spp. They are about the same size as bloodworms, and they can sometimes be found among crustaceans living in ponds. However, they are rarely found in such large quantities as to constitute a separate type of food. Fish love them very much, but these larvae are predators and should not be used as food in those aquariums where there is fry.

Black mosquito larvae can reach 1 cm in length and usually hang in standing water directly below the surface. They breathe air using a small tube that draws in atmospheric air just above the surface of the water. At the slightest sign of danger – even when a shadow falls on the water – they dive into the depths, so the net should be moved imperceptibly. Horse and cattle feeders, ponds, and even buckets of rainwater can be rich sources of these larvae. They can be caught and transported in the same way as Daphnia, etc. Fish love this food very much, and there is no evidence that it can be fraught with any danger. However, be sure to ensure that all the larvae are eaten – otherwise, in the tropical conditions of the aquarium, they will quickly turn into mosquitoes!

fish food


As food for aquarium fish, many different worms are used. Some worms are specially grown, others are harvested in nature or bought.
Earthworms are an excellent food for aquarium fish. Before use, they should be rinsed in water to clear the soil, and then fed to the fish whole or cut into pieces – depending on the ratio of the size of the worms and fish. They can also be crushed in a kitchen mixer (best of all in a special mixer that serves only for this purpose) – in this way you can cook excellent food for fry.

Worms can sometimes be bought, but for most aquarists, this food is a free complimentary product from gardening. Remember that earthworms should not be collected in land recently treated with pesticides or other chemicals.

These worms can also be bred in large crates, usually wooden ones. Boxes are filled with compost rich in organic matter. Worms are fed plant waste from the kitchen, laying them on the surface of the compost. If the box does not have a bottom and stands directly on the ground, the worms will populate it themselves, and then, when you collect them, they will populate it again, if only to maintain the necessary food supplies for them there. Of course, if there is no food in a box without a bottom, the remaining worms, being free, may well leave it.

Alternatively, you can use boxes that are closed on all sides, but they will not give such a big “crop”, as it takes some time for the worms to be able to multiply and replenish the population. The advantage of artificial breeding of worms is that in this way it is possible to maintain a supply of worms even when the garden freezes (using thermal insulation) or when the earth is hard as a stone as a result of drought (using watering). The worm culture should be in the shade so that in hot sunny weather they do not overheat.

Tubifex tubule is a small (approximately 2.0-2.5 cm long) reddish worms living in the wild. Usually, they are found in accumulations of dirt and garbage – for example, gutters, and collecting them is not a pleasant undertaking. It’s better to buy these worms at pet stores. We note at the same time that despite the assurances that various disinfectants and mechanical methods are used to clean the tubule, it should be emphasized that feeding fish with a live tubule is one of the surest ways to bring some kind of disease into the aquarium. Therefore, although we do not deny that fish love this food very much, it’s not worth the risk. It is much safer to use freeze-dried tubule or frozen and disinfected.

Enchytraeus (Enchytraeus spp.) – these are worms about 1-3 cm long, white. Sometimes they can be found in soil rich in organic matter. But for use as an aquarium feed, they are usually grown artificially using a culture acquired in a store. They are bred in a shallow (4-5 cm deep) plastic or wooden box of suitable sizes (for example, 20 x 30 cm), into which loose, rich in organic soil (substrate) should be poured; you can mix it with peat. The soil must be kept moist, in no case brought to dampness. For this purpose, the worm culture is usually covered with a sheet of glass, and on top with thin plywood, cardboard, etc., since the worms, in addition to everything else, need darkness. However, the culture should not be hermetically closed, otherwise the worms will suffocate.

An Enchytraeus culture can be fed with one or more pieces of bread soaked in water or low-fat milk. Other types of food for worms are cereals, such as oats. Some aquarists feed their worms with aquarium food – cereal. It should be remembered: no matter what food you give the worms, it must be wet. The amount of food and the frequency of feeding needed for the worms are established experimentally, and if the food begins to decompose, it should be replaced.

Worms should not be harvested until the culture is fully operational. This can be determined by lifting the lid, by the accumulation of worms gathering around the food. In addition, you do not need to collect too many worms. They should be taken with tweezers. If the substrate has the desired consistency and moisture content, the worms usually appear clean and can be fed to fish immediately. Otherwise, rinse them in water. You can feed them fish with the help of a special feeder-realer (which can be purchased at pet stores), designed for fish that feed on the surface of the water and in its middle layers. The bottom-fed fish can simply be thrown into the aquarium.

The old culture of worms is gradually exhausted and becomes less prolific, and it needs to be allowed to rest, replacing part of the substrate. After that, it will take about a week for the “yield” to increase again. You can establish a new culture, using part of the old for “sowing”.

Grindal worms are a smaller (0.5 cm long) species of Enchytraeus. They are sometimes used as food for grown fry or small fish, such as dwarf cichlids, small tetras, etc. These worms are bred at home, and the starter culture can only be ordered from specialized suppliers. The substrate should be the same as for breeding enchitrea, but Grindal worms are usually kept in smaller containers, such as plastic sandwiches. The worm culture should be covered and kept in the dark. You need to take some cereals (for example, oats) and scatter them on the surface of the compost in a small area, forming a circle with a diameter of 3-4 cm, then slightly moisten and cover with a small piece of glass. When the worms eat this food, a lot of them will accumulate on the underside of the glass, and from there they can be washed directly into the aquarium. These worms are too small, so they do not need to be rinsed to clear the soil. After some time, already having experience in breeding Grindala worms, it will be possible to establish the necessary consistency and humidity of the compost, in which it will not stick to the glass. Grindal worms are not very fertile, so care should be taken not to collect too many at once, otherwise, you can over-exhaust the culture.
Microworms are usually used as food for fry, but they can also be fed to very small adult fish.

Other possible live food

Woodlouse is very fond for fish of different sizes – from medium to large, although they may take some time to learn how to grab them. Larger fish likes crickets – they can be bought at pet stores specializing in reptiles (lizards, etc.).

Flies and other insects, both terrestrial and aquatic, can also be a delicacy for fish, but those that go for food should not be exposed to insecticides, that is, they must be caught, not sprayed! Domestic flies, as well as white, green and black flies, are suitable for this purpose. Stinging insects best be avoided. The maggots that serve as bait during fishing are sometimes also used as live food for aquarium fish, but you should not use painted larvae for this purpose since the paint can be toxic.

Maggots are best kept in a bait box or in some other plastic container with a tight-fitting lid with holes for air access. Larvae of flies, like larvae of mosquitoes, can turn into adult insects, especially when warm, and as soon as you open the container, the whole house will immediately be filled with flies! For this reason, to artificially slow down their development, they should be kept in the refrigerator. Drosophila, or Drosophila fruit flies, preferably wingless, can be bred as food for fish that feed exclusively on the surface of the water. The source culture, along with instructions, can be purchased from some pet suppliers, such as those that specialize in reptiles or amphibians. Fruit flies are usually bred in glass bottles filled with a mixture of oatmeal, sugar, and yeast and corked with sponges.

Some fish are very fond of fragmented water snails, but for this purpose only aquarium snails should be used, since wild ones can be carriers of parasites.

fish eating

Live fish

Live fish can serve as food for predators, although most of them can be taught to eat dead fish (see the “fresh food” section below), as well as other types of food for predators, as soon as they learn to associate with food what their owner puts in the aquarium. However, some aquarists seem to deliberately feed live fish or even live mammals (eg mice) to predators, especially carnivorous piranhas, and enjoy this “performance”. Fortunately, the use of “fish-feeders” – healthy fish bought exclusively as food for predators – has not been widely recognized in some countries, in particular in the UK, and many believe that such a practice should be universally condemned.

Fish-breeding enthusiasts sometimes use fry that is ugly, weak, or redundant for some other reason as food for other fish – after all, this is the fate of most fry in the wild. The rejection of fry is necessary when breeding fish that produce numerous offspring, especially if the need for young fish is small, as, for example, in the case of Central American cichlids. The use of weak fish as feed is generally considered acceptable, given that they would still have to be disposed of one way or another.

It is very important in no case to get rid of sick fish, feeding them to other fish, as this can lead to the transmission of diseases. For the same reason, do not let the fish feed on the bodies of dead or dying aquarium neighbors.

Fresh food

Many types of human food are also suitable for fish. Fresh or frozen green vegetables – cucumbers, peas, spinach, and lettuce – are the ideal complementary food for omnivorous and herbivorous fish. Some fresh or frozen vegetables are not easy for fish to digest and should be processed before use. Boil the peas to soften it or remove the skin, and lettuce and spinach are supposed to be blanched in order to destroy indigestible fiber.

It is better not to feed the fish with the meat of mammals or birds, as this can lead to the accumulation of harmful fatty deposits in the liver and other tissues. Despite this risk, many aquarists still advocate feeding fish with beef heart or liver. However, there is one golden rule, which is that if it is worth feeding such products to fish, then only in very small quantities. Fresh or frozen fish, shellfish (such as mussels), and shrimp, on the other hand, are excellent fish food. Warning: in no case do you feed fish with bread, biscuits, cheese, or cheese products, as they all contain saturated fats that are harmful to fish.

Food for fry

Fish fry of many species eat only live prey, mainly because they generally do not perceive stationary food as food, at least in the beginning. However, in some cases, the fry can learn to associate the approach of an aquarist with food, and then they will try everything that they are offered. Suitable small live food for growing fry are ciliates, Artemia nauplii and micro worms.

Ciliates (microorganisms) are needed as the very first food for tiny fry. Older aquariums overgrown with algae may contain a sufficient number of naturally occurring microorganisms. But in spawning grounds, where conditions are usually more sterile, there are no ciliates and they have to be bred artificially. To do this, put some plant matter (usually crushed leaves of lettuce) in a jar of water and put in a warm, sunlit place, such as on a windowsill. Water for the culture of ciliates needs to be dechlorinated, it may be water from the aquarium, otherwise, it is dangerous for the life of ciliates. When the water becomes cloudy, it should be added with a pipette in small portions (so that the fry do not cool) to add to the aquarium with fry. In pet stores, you can buy substitutes for ciliates.

Artemia nauplii freshly hatched from eggs are a very suitable first food for many fry or a second food for teenage fry, capable of eating only microorganisms in the first stage. Artemia has a double advantage – they are mobile in open water, clearly visible and attractive, and their orange color usually shines through the transparent abdomen of the fry that ate them, indicating that these fry receive enough food. Aquarists usually remove artemia nauplii from eggs (in fact, these are not eggs at all, but vesicular larvae), which can be purchased at pet stores. This process takes place in a container with salt water – it can be a large can, a plastic bottle of lemonade, or a specially purchased incubator. The required salt concentration may vary depending on the origin of the population (see package instructions). The culture needs intensive aeration for the constant circulation of larvae. The container must be kept in a warm place at a temperature of 18.5-26.0 ° C. The period of release of nauplii from eggs depends on temperature, but usually, it is 36-72 hours.

To collect nauplii, turn off aeration, and position the light source as close to the container as possible at about half its height. Shrimps will gather closer to the light, while eggs from which nauplii have not yet emerged, and discarded shells usually float on the surface of the water or drown and sink to the bottom. Thanks to this, the shrimp can be separated using a pipette or simply drained.

Otherwise, some fry may swallow the shell or eggs and die. Water with nauplii should be filtered, using a special sieve for live food or a small net with small cells, and then rinse the nauplii in clean water. In no case do not pour the shrimp into the aquarium along with the water in which they were bred, as salt water can destroy the fry. After collecting the shrimp, aeration should be turned on again. Artemia culture will give food for two to five days, depending on how much it is needed. To ensure sufficient feed, a continuous crop sequence is required.

fish food

Microworms are a suitable food for fry; they can be fed in parallel with or instead of Artemia nauplii. Breeding microworms is much more profitable than artemia, since this culture is cheap and easily propagated, representing an always available supply of food. Starting culture can be obtained from other aquarists. The only drawback of these worms is that they cannot swim and drown, albeit slowly. True, the fry for the most part grab them right away or swim to the bottom for them. For the fry of bottom species, microworms are more suitable than artemia nauplii.

Microworms are usually bred in a plastic container (a box of margarine or mayonnaise is suitable). A layer of oatmeal with a thickness of 1 cm is poured into the container, then moistened with boiling water to form a thick dough. Do not mix the dough, otherwise, it will spread across the walls of the container, and they should be kept clean. When the porridge cools down, add the starter microworm culture there. Cover the container with a lid so that the crop does not dry out, but air can enter, and put in a warm place (for example, on the lid of the aquarium). After a few days, the worms will multiply to such an extent that they begin to crawl along the plastic walls of the container, not stained with porridge, and they can be collected from there with a finger, cotton swab or brush, and then washed off with water in the aquarium.

A microworm culture can remain active for three to six weeks, but after about ten to twelve days, it starts to produce an unpleasant odor. Therefore, it is better to establish a new culture before the old culture reaches the stage of bad smell, because oats are cheap and culture is expensive! This time, as a starting culture, you can simply use a tablespoon of the old culture. If a lot of fry emerged from the eggs, then it is better to keep two or more cultures of microworms at the same time.
Daphnia nauplii, Daphnia nauplii, Cyclops Cyclops and Bosmina Bosmin (see above) can also be used as food for fry.

Fish feeding. Conclusion

Inexperienced aquarists often make the mistake of overfeeding their fish. This usually has the most unpleasant consequences. Excessive feeding does not always cause direct harm to the fish, but it can lead to serious problems with water quality, which can cause stress or even death to the aquarium inhabitants.
The harmful effects of overfeeding basically come down to two aspects:

  • uneaten food quickly decomposes, resulting in ammonia.
  • Excessive amounts of food (especially protein) absorbed by fish leads to increased fish ammonia release.

The increase in ammonia that occurs as a result of these processes can cause depletion of the biological filter resources, and this leads to the accumulation of ammonia toxic to fish in the aquarium water. In the case of regular overfeeding, the biological filter can adapt to this and cope with elevated levels of ammonia. However, the end result will be increased organic pollution, which can lead to the massive development of parasites, such as planaria and snails, as well as the increased formation of nitrates. In the latter case, a more frequent change of water will be required to prevent nitrate poisoning of the fish and the phenomenon associated with an excess of nitrates, such as the “bloom” of water (rapid development of algae).

If you want to know more about the ammonia and nitrogen cycle in an aquarium click on this link.

It can be concluded that fish require much less food than other animals of the same size. This is partly due to the fact that fish are cold-blooded (poikilothermic) animals and therefore they do not need to turn food into heat. Many fish are capable of neutral buoyancy, so they do not need the energy to overcome the force of gravity. Thus, if you compare fish with other animals of the same weight as them, then the fish require less energy.

When the aquarist gains sufficient experience, he will learn to count the strictly necessary amount of food. But for beginners, there is one important rule: at one time you should give the fish as much food as they can eat in about five minutes. If the fish are overfed or a large amount of their food accidentally enters the aquarium (for example, a jar of food has fallen), the excess must be removed from the aquarium as quickly as possible before it begins to decompose.

As mentioned earlier, possible types of food and frequency of feeding depending on the type of fish, and in addition, environmental factors can affect them. Most fish species, as well as fry of almost all species in nature, eat continuously, so it is better to feed them in small portions several times a day than give a large portion once a day. When keeping a common aquarium with many different fish, it is usually recommended to feed them two or three times a day in small portions. The exception is fish that feed on large prey. For example, some predators can eat a whole fish, which is only half the size of themselves. Such fish need to be fed only two to three times a week; they may even refuse additional food if they are offered it.

The aquarium should be closely monitored so that all fish constantly receive their share of the food. Fish swimming too slowly, as well as timid fish and fish leading a nocturnal lifestyle, may well skip feeding time. The same applies to individual fish at the lowest level of the aquarium hierarchy.
And finally, feeding time is a great opportunity to check if all the inhabitants of the aquarium are in place and in good health. Loss of appetite should always be seen as a warning signal that something is amiss.