Feeding

Fish Feeding Issues

Written by George J. Reclos, Andreas Iliopoulos and Michael K. Oliver Wednesday, 21 March 2001 01:00

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Feeding your fish is not as easy as it sounds. It is a complicated issue that requires you to know which is the best food for each fish, what its system will metabolize most efficiently, and which food will give the fish the essential and non essential elements that are all vital for its well being. To get the best results there are two things you should know: What your fish eats in the wild, and why it is important to follow specific feeding procedures, as well as using specific foods. 

There are two main groups of fishes according to feeding requirements: the Carnivores (flesh eaters, predators) and the Herbivores (plant eaters). We may also form a third group, the Omnivorous species that use a broad spectrum of food resources. Even so, there is a vast diversity among the biotopes that constitute natural ecosystems, the species that inhabit them and how they eat and are eaten.  This classifies some species as specialized feeders due to their particular sources of food and the methods they use to obtain it.

Predators may feed on invertebrates, mollusks, insects, plankton, and finally, other fishes. These we can define as general invertebrate feeders, molluscivores (snail feeders), insectivores (insect eaters), zooplanktivores (zooplankton eaters), and piscivores (fish eaters).

Some species sift for invertebrates (Geophaginae); others hunt them (Pagellus bellotii), or pick them with their sensitive vibration detecting organs (Aulonocara spp.the African peacocks), while some just browse upon them (Neolamprologus cylindricus).  

Some of the molluscivores have strong jaws and teeth so that they can crush snails (Neolamprologus tretocephalus), while others have mouths that are constructed in such a way that they are able to suck mollusks out of their shells (Botia macracantha; the clown loach).

Insectivores’ tastes differ a lot from species to species. Some consume insects when they are either eggs or larval stages, while others eat the adult insects. Many of them consume insects in all the forms of their life cycle. The mouth of such species is directed upwards so that they can easily prey on insects on the water surface (Gambusia spp). Usually fishes, as fry, are fed on insects while they are in egg and larval forms.

Some of the more specialized feeders are fed on adult insects located over the water level. They capture them either by jumping (Osteoglossum bicirrhosum; the Silver Arowana) or by spitting water on them (Toxotes jaculator). Adult O. bicirrhosum jump out to catch birds and arboreal mammals as well. Plankton is found in either free-swimming form or on different substrates, so planktivores have either to pick at it (Cyprichromis spp.), suck it from the substratum (Gnathochromis permaxillaris), or filter it through their suitable pharyngeal teeth (Cyprinodontidae) or their filamentous gill rakers (e.g., Benthochromis tricoti).

Piscivores utilize several, and sometimes odd, feeding behaviors that depends on the prey. This is also based on their size, their environment, and their body structure.

These we can group into hunters, stalkers, suckers, opportunistic fish eaters, egg eaters and scale feeders. The way they capture their prey is dependent on their jaw and teeth structure. Hunters perform either ambushes (Nimbochromis livingstonii), or they run after their prey (Dimidiochromis compressiceps). Stalkers are usually bottom dwelling species that bury themselves to ambush their prey. Some of them display very good camouflage (turbots, family Scophthalmidae), or they may have wormlike appendages on their heads or near their mouths to attract their prey (Stargazers and Anglers). Some of them, though, live under fish schools and stalk them from underneath. The nurse shark Ginglymostoma cirratum, for instance, sucks its prey from holes and cavities, in contrast to other shark species that hunt and capture their prey. Opportunistic piscivores can be any fish that are able to capture and consume another fish, especially if the prey is younger, smaller, weaker, or ill. These species are observed to prey on other fish mostly during seasonal changes of physicochemical parameters (e.g.,  lighting) or during breeding times (Cyphotilapia frontosa). The egg eaters have no specialized techniques, and most of them feed on eggs only occasionally, although some species will seek other fishes’ nests for eggs (Telmatocromis spp.) to feed on. The scale eaters (e.g., Plecodus straeleni, a Lake Tanganyika cichlid) have teeth and body shape that enable them to attack and remove scales from other fishes. They are rarely kept in home aquaria for this very reason. The truth is that they do not, most of the time, severely harm the attacked individuals in the wild.

Herbivores usually feed on underwater vegetation consisting of plant plankton, micro and macro algae, as well as detritus. There are phytoplanktivores that also pick, suck, or filter plankton. The algae eaters scrape, comb, nibble, or scoop algae from the surfaces on which algae grows, while the ones that feed on detritus scoop mud methodically for “greens”. The feeding techniques mentioned above are quite common in the several different herbivorous species of Tanganyika (e.g., Tropheini, Eretmodini, etc). There are a few species that consume the filamentous algae (Epalzeorhynchos siamensis, E. kalopterus), and they are very useful as tank mates due to this feeding preference.

Another source of food in the wild is parasites. These are little organisms that use fishes as hosts. External parasites are found on the body surface, under the operculum and inside the mouth. If there are many of them it is a problem. Some of the freshwater species of Mochokidae and the marine Labridae are famous parasite cleaners. Wrasses (Labridae) lack this behavior as adults except for the Labroides dimidiatus, L. bicolor, L. pectoralis in the Indian Ocean and Symphodus melanocercus in the Mediterranean Sea. This same behaviour is also witnessed in some species of shrimps (e.g., Urocaridella antonbruunii). These species make actual cleaning stations and have regular visitors. They wait uncomplainingly for their turn, and while they are being cleaned they offer wide opened mouths and gill covers. Parasite feeders are also useful in tanks because they control the population of external parasites.

Omnivores are either opportunistic feeders or scavengers (Anguillidae), and they can consume whatever they find, from corpses to terrestrial trees’ fruits, depending on seasonal availability (Acanthophthalmus kuhli). There are some species that it seems feed on faeces (Scatophagus argus). These species can be fed on every single food item they find.  Even aquatic birds and reptiles (commonly terrapins and sea turtles) have been found in omnivorous fishes’ stomachs. In the bigger species’ stomachs there have been found pieces of boats or even oil barrels. These fishes may not be omnivorous, but their enormous size helps them to consume nearly everything. This makes large specimens, or fishes that grow a lot, difficult tank mates.

Following this introduction we can now understand which way our fishes must be fed in captivity to feel like home. Also, it gives us a clue for the equipment and the suitable aquascaping needed for their housing. And as long as feeding produces wastes that we must get rid of, we have to know the type and capacities of filters that are the optimum for this task. We can also conclude that their dietary needs are critical for their health and behaviour. But as long as different proteins and amino acids exist in these different foods, I am led to the inference that it would cause problems sooner or later. Even if no obvious health problems could be detected (very unlikely), surely some behaviour problems may occur. All of us have noticed unexplained deaths and strange behaviours in our tanks. When we keep some particular species, we want these species displayed in our tanks the same way as if they were living in the wild. There is no need to mention the health problems that can be caused when we attempt to feed herbivores with mammalian, or even non herbal proteins. “Malawi bloat” and “Tropheus disease” are very well known problems.  Improper feeding is also considered as guilty of causing “dropsy” as well.

Getting some basics of biochemistry is essential if we are to understand why feeding the right food is really important. Of course, it will be a simplified approach, since the task is to learn something, not get a PhD on it. We all know that DNA is the genetic material of most living organisms (some viruses excluded). We all know that DNA is located in the nucleus of the cell and is responsible for us being humans, or making an Aulonocara species different from a  Nimbochromis species. We can see that the differences between these two species are many and important. They differ in their feeding, breeding and even swimming habits. They also differ in size, temperament, color and shape. Although environmental conditions may play a role on how they look (a fish living in a nutrient-poor environment will never reach its “programmed” final size), still the major factor determining all that is the DNA. This is something that has become known to almost everybody. What most of us do not know is that DNA has only one function – keeping the codes for the production of proteins.

So actually, the fish will look as it looks only because it is producing the specific set of proteins encoded by its DNA. So far, so good. Well, proteins are formed by small molecules linked together, the amino acids. If we are to visualize a protein as a wall, then the amino acids are the bricks. Every protein is a chain of specific amino acids in a strictly specified sequence. A DNA molecule is also a chain of specific bases in a specified sequence. Since the protein comes from the DNA then there must be a transcription code. Well, there is. Every three bases of the DNA chain code for one specific amino acid. When the DNA is “read”, the cell adds one amino acid for every trio of bases read. Depending on the number of amino acids added, the resulting product is called an oligopeptide (small number of amino acids), a polypeptide or finally a protein (which may contain thousands of amino acids). If a wrong amino acid is added in the protein chain then the resulting protein may not work or even cause damage to the organism. This is usually a genetic problem (point mutation, which means the wrong base was present in the DNA) or a problem of the transcription of the DNA. No matter what, nutrition has nothing to do with it.

However, if an amino acid is not found in the cell (as a result of malnutrition), then the peptide or protein will not be produced by the cell. The impact this may have on our fishes is obvious. You see, among other things, enzymes and some hormones are made of amino acids, too! Enzymes are absolutely essential in almost every chemical reaction that takes place in our fish (which would be otherwise impossible to take place at 26oC at a reasonable speed), while hormones control some very important aspects such as size and growth, sexual activity, maturation, etc. Enzymes are also essential to utilize hydrocarbons and lipids (the other elements in food besides proteins) during digestion. In short, without enzymes and hormones every reaction in the fish would stop.

So amino acids are the bricks every organism is made of. The amino acids are further classified as essential and non-essential. The essential ones are those that the organism (our fish in this case) can’t produce by itself and relies on its food for. The non-essential ones are those that the fish can build by itself. So, the essential amino acids must be found in order to survive. When fish take their food, it contains proteins, which are broken down (catabolism) to amino acids that are used to make its own proteins (anabolism). Schematically, the fish breaks down the wall, selects which bricks it needs and then throws away the rest (in the form of wastes). Since every protein contains different amino acids, if the fish doesn’t get the correct proteins, it will not get the essential amino acids it needs which – remember – it can’t synthesize by itself. During millions of years of evolution, fish species have adapted in specific environments that can supply them with the proteins they need. Insectivores eat insects because only insects contain the right proteins for them.

Feeding them spirulina pellets in our tank will not give them the proteins they need. They will eat it because they are hungry, but some amino acids will not be there. Their intestinal tract, as well as their whole body, is specially designed to absorb and use this kind of proteins, not just any protein. As time passes by, the fish will develop a “shortage” in one or more of the essential amino acids and – sooner or later – will die. Unfortunately, there are no “alternative biochemical pathways” since this would be a tremendous waste of energy, and nature hates that. Herbivores have a longer intestine with special mucosa and a batch of enzymes to utilize vegetable matter. Feeding them beef heart will shortly kill them. Feeding herbivores or insectivores with foods that contain too much fat (especially animal fat) will also cause very serious health problems. Their peptic system will not work normally in the presence of all this fat simply because it was not designed to. An organism can’t simply adapt to the foodstuff we give it in a month or a year. It takes thousands (even millions) of years to adapt to such a change. Please remember that many species have been extinct simply because a specific food source was eliminated from their environment. In extreme cases, they became extinct because only one element was depleted from their surroundings.

Amino acids and peptides were used for this analysis only because proteins, hormones and enzymes are the chemical names most hobbyists are familiar with. However food consists of three equally important groups of substances: proteins, fat (fatty acids, saturated or not) and carbohydrates (e.g. sugars). Proteins are used for “building” or “repair” purposes, carbohydrates are the main source of energy while fatty acids are used for many purposes (energy storage being one of them).

The same facts that apply for the proteins apply for fatty acids and carbohydrates. Fish (as every other living organism) can utilize specific fatty acids and carbohydrates (you guessed right; there are many of them). Moreover, their daily needs call for a specific mixture of the correct elements. Thus, you can’t feed your fish a diet based exclusively on carbohydrates since it will soon develop symptoms of severe malnutrition. The same will happen if you feed it carbohydrates that it can’t metabolize effectively (or at all).

What should we do then? There are some general rules that, if followed, will ensure well-fed fish with minimum problems.

Try never to overfeed because fishes in the wild are not always full. It is not so easy to be fed on a regular basis if you have to live in a hostile environment while trying to grow, not to be eaten and later increase the population of your own kind. Also, natural environments are usually oligotrophic, meaning there is not as much food as we may think there is. So, nutrients are available in very low concentrations or are totally absent. This forces the fish to make the best use of any available sources and may lead to further adaptation. Indeed, it is well known that that the so called "Competitive Exclusion Principle" is applied in every biotope known to man, Rift Lakes included. According to this, two (or more) species can't feed on the same food, in the same way, at the same place and time. If they were, one of them, the fittest would survive at the expense of the less fittest (survival of the fittest). Therefore it becomes apparent that two (or more) species feeding on the same food should in fact be feeding on only a very particular subset of the total available food. 

Thus, it has been shown that although many mbuna species may be feeding on the algae found on the same rocks, in the same area, their special trophic adaptation allows them to eat different parts of it (upper layer, algae found in crevices etc). Moreover fish know which species compete directly with them for the same subset of food and direct their aggression to those species only. Of course, the first candidate is their own species which partly justifies the intraspecies aggression of most mbuna, even against their own females.

This was also demonstrated by a recent study which showed how fourteen species of Lake Tanganyika cichlids feed on the thirteen species of shrimp found in the Lake. It was shown (among others) that within the same shrimp population, larger cichlids prayed on larger shrimps while smaller fish were capable of eating the smaller shrimps which evaded the larger cichlids easier.

It is evident that in nature food is not everywhere, not all the time. Fish have developed special skills in order to effectively use the sources available. This means that they are not fed "2-3" times daily and their bellies are not always full. Please remember that the fish we keep in our tanks are built to cope with this kind of environment. Feeding them sparingly, or even every other day may seem cruel but it is the best approach. If we test our fishes’ native waters we shall find no nitrates and no phosphates such as we can measure in our tanks. It is more important for keeping fishes healthy if the water (environment) is clean and clear, than how much we feed, as long as the “best qualified” foods are provided.

Only fry and semi-adult fishes need more than one feeding per day. We feed adults more heavily only during breeding. But we give foods with minimal fats because we do not want delivery problems for the females from fats accumulated around their vents.

Try to feed the right food, not just any food your pet shop carries. Herbivores need special food, as do all the other feeding categories listed at the beginning of this article. “All around” foods are a compromise and should be used alternatively with specialized foods.

If we research fish biology more thoroughly, we shall find out that many “life styles”, foods, and behaviors are present in the underwater world. Feeding fishes is not just shopping at our local pet store. We hope that the data presented in this article make this very clear to every hobbyist.

*NB. Please note that the links are no longer working. We left them in for the sake of completeness of the original article.