Reducing Aggression in the Cichlid Aquarium

What is it that draws aquarium enthusiasts to Chichlids? What else, but our adoration of their spectacular colours and their unique mannerisms! Or could it be that we all admire  their extrovert personalities, their intricate social behavior and the astonishing degree of intelligence they possess? Or could it just possibly be that their most famous trait — aggression — sometimes so perfectly mirrors our own?


Lake Malawi is Africa’s third largest and second deepest lake, and also the world’s tenth largest freshwater lake. The 1000 species, or more, of Lake Malawi cichlids include some of the most beautiful fish in the world, fresh water or otherwise. Indeed, African cichlids are known in particular for their beautiful array of colors and patterns.

Lake Tanganyika lies in the great rift basin of East Central Africa, and is the seventh largest, and the second deepest freshwater lake in the world, with approximately 250 different Cichlid species and more than 150 species of other fish. Moreover, the lake has two record breaking dwellers, the world’s largest Cichlid with a length of 80 cm and the world’s smallest Cichlid that is only 3.5 cm long. The area of the East African Rift Valley has active volcanoes, which makes the  lake water quite alkaline, but also very rich in minerals. It is important to keep this natural habitat in mind if you plan to keep Lake Tanganyika Cichlids. Within this lake there are three main biotopes:

  • Open water with a sandy substrate.
  • Rocky substrate, located around parts of the shoreline and also underwater reefs and
  • Shell beds, found in the form of piles of empty snail shells that litter the floor in different bays.

Different kinds of Cichlids evolved from each biotope and are therefore attracted to exploit that particular environment. The Lake Tanganyika Cichlids thus differ in body shape from the uniform shape of Lake Malawi Cichlids, and also differ greatly in their feeding habits.

Lake Victoria is in Central Africa, and is the third largest freshwater lake in the world. The lake has a large variety of Haplochromines and a few Tilapines.

It is important to remember that each of these lakes have their own definite water parameters, which you should always heed, depending on which Cichlid species you want to keep. We will provide a table of these parameters at the end of the cichlid pages.

The Cichlids of Africa, renowned for their proliferation, are among the easiest aquarium fish to breed. With very few exceptions, African Cichlids, especially those fromLake Malawi, readily adapt to life in captivity. They are very hardy, and they are easy to maintain – but to keep and display them at their best, they do require relatively large aquariums with the kind of aquascaping that not only allows plenty of space for swimming, but takes accord of definitive delineation between areas, as well as caves and plenty of hideaways, to ease territorial possession.

However, if you want to keep Cichlids, you will need to learn how to read and understand their colour changes. Cichlids express dominance or timidity through their coloration: a pale fish may be a stressed or submissive fish, whereas a bright fish usually is a dominant or aggressive fish – and always the number one choice for mates. During breeding the males become flamboyant. When males lose their territory, they also lose their bright colouring. However, some try another ploy: They go into hiding, but retain their colours to pretend that they are still dominant, so hoping to attract potential mates.

African Cichlids are highly predatory and extremely territorial. In the wild, they often live together in groups or schools of like species. Mature Cichlids guard their territory and they are not hospitable at all – frequently behaving aggressively to con-specifics, and especially to Cichlids of a different species, but a similar colouring. In nature all is not perfect as we sometimes think – fish do die from conflicts and disputes. But in an aquarium, Cichlid aggression can be your biggest headache!

While aggression is probably one of the hardest aspects of African Cichlids to deal with, many ingenious hobbyists have overcome, or at least subdued aggression to the point where a relatively tolerant community can be had. In all honesty, Cichlids show their most vibrant colours and pugnacious attitude during disputes -  so the goal is not really to destroy ALL of this activity, but to limit it to the point where you don’t wake up every morning with a “victim” floating at the surface.


While not all Cichlids are super-aggressive, and many are even outright docile, there is a definite hierarchy in the cichlid aquarium. The largest Cichlid is usually the dominant one and will behave aggressively towards all of the other inhabitants. During mating and territorial disputes, this aggression can progress to tail beating, as the dominant Cichlid attempts to push water at its enemy to show off its power. If he has a defiant opponent, this situation can and often does escalate into to genuine combat, which can include mouth-locked wrestling and a lot chasing in an attempt to bite each other. If this behavior persists you may have to separate the warriors, for it will surely go on till one dies. The smallest Cichlids in the aquarium may also occasionally be attacked and even killed by the larger, more dominant fish.

However, aggressive behaviour can be dealt with in five ways. (I urge beginners to pay attention here – just as I recommend this section for Cichlid keepers who have recurring aggression problems)

The primary reason for Cichlid aggression is driven by food — the lack and availability of food, as well as the competition for it. Cichlids are greedy and fast feeders. You can control aggression by feeding your fish less, but more often. Cichlids are territorial because they want to stake out their own backyard garden from which to hunt and harvest. Con-specifics (especially  similar looking fish) are seen as a threat, because if they are similar, they are perceived as competing for the same foods and they will therefore be chased off.

The first way is one of the simplest techniques to reduce tank aggression levels and is unfortunately also one of the most overlooked -  simply because it involves a little forethought and planning before the fish are even introduced. It involves selecting species that are compatible with each other. ‘Compatible’ in this case refers to several factors: water conditions, size, color, typical aggression and activity levels, and finally the levels of tank habitation.

Let us begin with water condition: it should be obvious that while it is possible to keep fish from very different water conditions in the same tank, none will truly flourish. So, it is always advisable to keep only species of cichlids from the same area with similar water parameters. This includes temperature, pH, and water hardness. As we saw, the two main “biotopes” of African Cichlids are Lake Tanganyika andLake Malawi. We recommend that you do not mix fish from these two lakes, although many hobbyists limited by tank space have claimed no adverse affects in mixing species.

Then there is tank size. This may sound like common sense, but it is easy to to forget that you must buy your tank for the maximum ADULT size of the species you want to keep. Cichlids do better in larger tanks. It is also advisable to start with juvenile fish and grow them up to size, as this creates better acclimatized fish, not to mention the lesser drain on your wallet. Be aware that if you buy full-sized specimens, they may be wild-caught and thus more difficult to keep. And yes we know – you might not be able to find 3 or 4 species you like that are EXACTLY 10cm long as adults – just do not put a 25cm carnivore in with a bite-sized fish. By keeping similar-sized fish, you reduce the burden of any one fish “being the smaller victim.”

Then we come to body colour. In most of the animal kingdom aggression is concentrated towards members of the same species, as these are the true “competition” in terms of survival and breeding. This is no different with Cichlids. Ask yourself: How do fish detect other fish of the same or similar species? They do so by the unique array of their colours and patterns. Similarly-coloured or patterned fish are going to be the most likely target of a fish’s aggression, as they see these fish as food competitors. The obvious solution is to keep fish of very different colours and/or patterns. There are enough species with different colours to satisfy even the most discerning aquarist!

As for aggression and activity levels: Not all Cichlids are as aggressive as some of the “bad boys” that have given Cichlids their reputation. Some are downright docile. It should make sense that keeping an easily terrorized species with a ‘bruiser’ may and usually will result in some bloodshed. Do some research! Books may not be the ultimate source of information. Ask experienced aquarists!

Finally, there is the actual habitat. Studies have found that the influence of habitat type on male aggression was one of the greatest triggers, and irrespective of the species is directed equally at con- and heterospecifics. In fact, it now seems that habitat complexity plays a much larger role in shaping aggressive behaviour than other suggested factors, such as competition for resources, or even spawning.

Add to this the different levels of tank habitation: Not all cichlids occupy the same levels in the water column of an aquarium. As in nature, there are rock-dwelling species, open-water schoolers that keep to the upper stratum in an aquarium, and just for variety, sand-dweller species that frequent the sandy lake bottom in open areas away from the coastline, such as the shell dweller. Put them together wisely, and not every fish will fight for the same niche or cave in the aquarium – immediately suggesting a good way for selectively controlling territorial disputes.

If you want to create a community of Cichlids, you need to aquascape your tank properly. Shelter and “hiding” spots are vital for cichlids to live in any sort of peace. A large tank and a built up rocky aquascape that curves in and out, creating many separate corners and zones, as well as plenty of caves and hides, hugely contributes to peace in the aquarium. The more areas of cover are available, the more chance that each fish will find a spot to claim for itself. But, you also need to aquascape with proper forethought – because you will still have to clean your tank, and you do not want to make life difficult for yourself.

You may want to keep in mind that different areas can represent different locations in the tank’s biotope. In a rift-lake tank, for example, have a high pile of rocks in one part of the tank to simulate the rocky coastline, and sandy open part in another area, to simulate the lake floor. Then, create an intermediate area to join these two areas, and decorate it with small rubble and perhaps some snail shells to make a shell dweller haven. This allows you to keep 2 or 3 different species together with minimal interspecies or territorial disputes.  In fact this is a tool that can be used with all kinds of freshwater aquarium fish.

Following these basic rules will solve 90% of your aggression problems.

While this is great for people who are still in the planning stages of a new tank, what can you do if you already have an established tank? There are several solutions. The first is to check your male/female ratio. Males are the more aggressive, and they tend to rough-up females not interested in mating. You should have at the very least 2, but preferably 3 females per male of a any given species, because then the male’s aggression and frustration is not taken out on just one female. Instead, it gets distributed.

Second, if you have not already maxed out the number of tanks you have, you can always isolate rougher pairs, or species into what is known as a “species tank” where only one species is represented. This obviously eliminates interspecies quarrels but – as we mentioned – most of the aggression in cichlids is towards their own kind – so you might end up with a lone victor as the only survivor of the species tank.

Change your aquascaping! Provide more territories! Introduce more females. And isolate breeding pairs. The latter can do a lot to calm the territorial fights that often occur in both species and community tanks, as breeding cichlids often try to own 80% of a tank’s length, with the other fish all huddled into the remaining 20%!

Also be aware, when you want to introduce a new member to an already established aquarium: One of the unique qualities of African Cichlids is their ability to recognize their tank mates and their owner. You can never fool them when you try to secretly slip in a new fish!  And cichlids do not make friends easily. So when you add another inhabitant, you will see competition for superiority and battles for territory.

The sixth and seventh techniques are meant specifically for reducing aggression in an already established tank. They are the use of target fish and “controlled overcrowding.” We will look at target fish first.

What is a target fish? The ideal target fish is hardy, built-like-a-tank, fast and agile, and somewhat expendible (should they ever get caught by the aggressor…well, you get the picture.) The role of the target fish is to act as a decoy in the tank to help vent both territorial and breeding aggression. Since the average target fish is faster than any of the Cichlid tank mates, it can better deal with high-speed chases and will more likely escape without harm. A side benefit of using target fish is that it gives the usually dominant male of a breeding pair a diversion and thus keeps his spouse from taking the brunt of the male’s territorial (and sexual) frustrations. Target fish will also induce better fry-defense, in those species that offer it.

Commonly used target fish include zebra danios (and the larger Giant and Pearl Danios with larger Cichlids) and Australian rainbowfish. These fish are generally readily available, reasonable in price, and very efficient swimmers. They are also very adaptable in terms of water conditions,  so they can be used in a broad range of Cichlid biotopes, both from Africa and South America.

The fourth way is a method called controlled crowding. Please understand, this is precision overstocking – not just a matter of filling your tank with more species.

This is not a recommended process for the neophyte aquarist. In fact, UNcontrolled overcrowding is probably one of the top reasons why beginning aquarists’ tanks fail: Essentially the bioload of the tank exceeds that of the filter and without very frequent water changes, the fish are poisoned and the tank dies off.

For controlled crowding, the hobbyist must be very confident in his or her ability to consistently maintain good water quality, even under heavy bio-loads. If you are at the point where you have a reasonably good understanding of the chemical cycles that control your tank water quality, and of the many methods of controlling these cycles, then controlled overcrowding can be very effective in reducing aggression. The process is no more than carefully increasing the number of aggressors in the tank so there are more fish than possible territories and thus territories are not readily formed. Without clear boundaries to defend, the fish become more tolerant of each other and since there are more fish, the aggression is diffused over more targets, while the victims have the possibility to get lost  in the crowd.

This method is based on the fact that crowding is a normal condition in the wild, where cichlids frequently occur in densities as high as 10-18 fish per square meter. However, Nature always has an open feed-back loop, in an enclosed environment like an aquarium, the use of controlled crowding necessitates using the best filtration your money can possibly buy!

The burdens of this method are many: careful planning is necessary to increase the abilities of your filtration system to meet the needs of the increased bioload. Another absolute requirement when overcrowding is a step-up in the frequency of water changes. Nitrates build up quickly in an overcrowded tank, and the easiest way to reduce levels is through water changes. Some breeders and advanced hobbyists who use this technique do daily water changes. Also , filters have to be watched carefully for clogging and must be cleaned out often. So, while controlled overcrowding (along with increased tank maintenance) can be an effective diffuser of Cichlid aggression in tanks, you should think long and hard before venturing into this method.

The eighth and final way to minimize aggression is just one sentence long and should really be applied in every single cyclid tank: keep your gender ratio at no less than three females per male!

Yes I know, I have said this a couple of times already. Yet I say it again, that is how important this is!

In final summary – it is relatively easy to keep cichlids. However you must have room for an appropriate size aquarium, and you must choose your aquarium size for the adult size of the species. You must provide your cichlids with an adequate environment, and your water quality, water temperature and the pH level should be of high quality and be consistently stable. The temperature of the water should not fluctuate up or down – but must steadily remain within the proper parameters. You must also have a long-term commitment to providing proper care, as cichlids have a considerable life span.


Breeding cichlids are a joy to watch, perhaps because the breeding behaviour among cichlids vary so much. Some lay their eggs on open surfaces such as rocks, leaves, logs, and substrate—this type of cichlid is called an open brooder. Others need to retreat into caves, or crevices to lay their eggs. For cave brooders it is essential that the aquarium has many caves and hides. Still another form of cichlid breeding is mouth-brooding, in which the mother fish carries her eggs in her mouth until they hatch. And then there are the shell-dwelling cichlids, which breed inside empty snail shells.

In all cases cichlids make the most devoted parents. With the open-brooding cichlids, both the male and female parents are involved in caring for their brood, with the male guarding the territory against predators and the female fanning the eggs to increase oxygen supply.

Mouth-brooding female cichlids are defended by their males and carry their fry in their mouth – but this also means that they go hungry during the entire breeding process. In some cases this may compel the female to consume either the eggs, or even the hatched fry. She needs to be carefully watched, and fed as soon as her fry begin to swim. Otherwise you may want to temporarily separate the female from the fry, or vice versa. Just remember that removing the female from her home tank has its own implications with regard to the social hierarchy. She will need to fight for territory all over again once she is returned!

If you want to know more about breeding, you can find this under the Cichlid drop-down menu above, because the topic deserves a page of its own.

The promised water parameters follow on the next page.