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Managing cichlid aggression in closed spaces

A cura di , 2020.
Ultimo aggiornamento in data 24-giu-2020

Juan Miguel Artigas Azas,

" Cichlids are not mindless killing machines, but possess a very sophisticated behavior that allows them to evaluate the use of aggression in face of their existential need to obtain or protect certain resources "

If you read my article “Cichlid aggression” by now you should know that cichlids are not mindless killing machines, but possess a very sophisticated behavior that allows them to evaluate the use of aggression in face of their existential need to obtain or protect certain resources. Those resources could be a breeding area, nutritious food, or their progeny.

In the wild, cichlid fishes are normally unconstrained in terms of space, meaning that when an individual is defending a territory against an adversary, after intimidation or a fight the quitter can just swim away and prevent any damage from being done. In the aquarium often this cannot happen due to the limited space, and the loser in a confrontation will receive the continuous harassment of the winner, this will happen mercilessly until it is dead, often in a very terrible state. Watching those confrontations can be very stressing, particularly when one sees a cherished fish being given no break after a confrontation. Worse yet, after the power balance is broken damage and death can come very quickly, depending on the species and the conditions.

Each territorial species has a natural territory size to protect, meaning that if a potential adversary is beyond those limits, it can safely escape the aggression of a territory defendant; the problem is that normally cichlids have a large natural territory size, and often aquariums are smaller than this. Some fish demand such a large territory size and are so belligerent that they are almost impossible to house in a regular (or even large) aquarium; those fish are not fit for captivity. An example of this is the Central American wolf cichlid, Parachromis dovii, which besides being a very active territory defender it can potentially grow to over 60 centimeters in length; an adult P. dovii would demand a territory radius of at least four meters, and if it is not given it will relentlessly (and quickly) try to kill any adversary.

Maschio adulto A pair of adult Parachromis dovii may protect a territory with a diameter of four meters. Foto di Juan Miguel Artigas Azas. determinatore Juan Miguel Artigas Azas

Other species, such as the angelfish, Pterophyllum scalare, or the Central American Thorichthys species, demand smaller territories, and even rather small aquariums can accommodate for several territory holders without problems. In these cases territory delimitation and defense is often a wonderful spectacle, one which provides a great deal of information about the species.

Aggression is not directed by a territory holder equally to every other intruder, it is focused on direct competitors; those species that are not seen as such are normally ignored, unless they can pose a risk to eggs or fry, in which case they would be chased away during breeding time.

So, a good information starting point when planning to keep a cichlid species in a close space is to know the approximate size of the feeding and/or breeding territory the species demands. Many species do not hold feeding territories, like Thorichthys or the angelfish, since they are social species that have evolved to feed together because that brings them an advantage; but some other species like the rocky reef dwelling Chidongo species from Lake Malawi do. Most species, however, demand a breeding territory, even if for a short period of time. As a rule of thumb, species that do not hold feeding territories are easier to keep in the aquarium — aggression wise.

If you are trying to maintain a cichlid species that defends a permanent feeding territory and you do not offer the proper space, you have to understand that only one individual can be safely kept. Of course that depletes you of a significant part of the experience since you would miss the interactions between conspecifics, but at least you have the choice to keep it. When talking about territorial species, some species will allow young individuals and/or females to stay in the feeding territories, while others won’t. Again, P. dovii being an example of this; sexes would just tolerate each other during breeding time.

In some cases territoriality is just maintained for breeding purposes. In this situation we have two strategies: species that guard permanent breeding territories and those which only do so during a given period of time. In the former case, once fish reach adulthood and males (normally) establish permanent breeding territories the space rule applies: conspecifics, or even individuals of other species that look alike, will be driven away from the territory boundaries constantly. Many mbuna from Lake Malawi fall in this category, for example Metriaclima species. If you want to keep more than one male of a given species, the proper space must be given for territories to be established. The good news in this case is that species which are no direct competitors for partners are often ignored; so you can effectively maintain a large community tank with several species that live together in harmony.

Male at Otter Point A male Metriaclima aurora, highly territorial males of mbuna cichlids should be kept only one male if not a very large aquarium space is given. Foto di Juan Miguel Artigas Azas. (04-nov-2008). determinatore Ad Konings

There are also species that hold harems, like many representatives of the Apistogramma genus, where a male will defend a very large territory (for its size) in which several females (and often younger or sneaker males) are accommodated. Herichthys minckleyi of northern Mexico is also a harem breeder, but in this case males defend enormous territories in which two or more females can breed — as you can infer this species is very aggressive.

Species that are aggressive just during breeding time can be handled with a variety of techniques. One is to offer a significant amount of hiding places, so that non-breeding individuals will be able to search for cover while the breeding efforts are maintained. Many Central American cichlid species fall in this category and it is possible for several individuals to be kept together when sufficient hiding spaces are given, even during breeding time.

In the latter case one should give consideration to the species kept, as some have evolved a more aggressive disposition than others. For example, even being relatively small cichlids, both Trichromis salvini and Neetroplus nematopus from Central America are very aggressive and have the motivation and skills to attack and defeat much larger adversaries, even when they are not direct competitors but seen as a threat to their descendants. In these cases even hiding places would not do to protect adversaries, since they will be chased even there. A solution to this problem is to keep a large number of individuals together in the same aquarium, so that aggression is distributed and not focused. Paul Loiselle coined the term “target fish” (1981) for this technique in his wonderful article “Matchmaking for cichlidophiles”.

When keeping a large number of specimens in an aquarium there are effects to take into consideration. One of them is of particular importance if your goal is to breed a certain cichlid species. A fish species will only reproduce if it is able to secure a territory for the extension of the breeding period. If a pair of fish is unable to hold a breeding territory they simply won’t breed and there will be no offspring. This is a common mistake when keeping fish, as it can easily go unnoticed that a pair cannot establish a breeding territory which is the cause it won’t breed.

The “rule of large numbers” would however often work very well when only one aggressive species is kept in an aquarium, in which case you can successfully maintain it in large numbers without aggression losses. In this case however you are faced with other problems. One of them is that a large number of individuals in an aquarium often means a large amount of dissolved metabolic substances often resulting in less than optimal water quality. Some species cannot cope with such a situation and problems like hole-in-the-head disease (Hexamitiasis) are then common. Worse yet, the species’ behavior is often affected when kept in large concentrations (just think of 40 humans’ potential behavior if kept in a small room) and you won’t be able to enjoy and learn from it. Some species, as mentioned however, have evolved group feeding and those would be suitable for this technique, which is better suited for securing a large group of adults that can later be distributed to properly sized quarters.

When keeping large pairs of aggressive bi-parental substrate brooding cichlids, like any of the Central American Herichthys, Parachromis, Amphilophus, Maskaheros, Mayaheros, etc, a particular technique which is called the “incomplete divider method” was developed in the mid 1960s by Guy Jordan, a founder of the American Cichlid Association. This technique is used in two different forms. In one the aquarium is partitioned (temporarily or permanently) with a divider of clear glass, except the glass does not go all the way to the bottom of the tank, but stays one to three centimetres (depending on the size of the fish kept) off the bottom. A male is placed in one half of the tank and a female in the other; the fish can then see each other and interact but cannot physically touch. In this form they cannot hurt each other but they can still spawn in the area just below the incomplete division, where if a spawn takes place, most eggs will still be fertilized. When using this technique you have to make sure you have a current flowing from one quarter to the next (preferably from male to female to carry the male’s milt to the eggs).

In the second way to use the incomplete divider method you split the tank in half with a porous divider, traditionally an egg crate diffuser. For this you need a sexually size dimorphic pair (the male larger than the female, or the opposite). You can then break away cells in the diffuser to make an opening just large enough for the smaller fish to fit, but not the larger. The smaller fish, typically the female, would then venture in the male’s compartment but can retreat to her quarters as soon as the male turns nasty. I have used this technique successfully on several occasions. Mating then can occur and the smaller fish out of harm’s way. One word of caution: be sure to firmly attach the divider, which is sometimes not simple, because it is easy to underestimate the male’s strength — which I did once with a large pair of Herichthys deppii. The male was trying to reach the female with such force that he was able to knock off the divider, after which the female was quickly killed. This all happened in less than an hour between my visits.

Adult in the aquarium A large male of Herichthys deppii can knock down an incomplete divider if not firmly attached. Foto di Lee Nuttall. (28-gen-2010). determinatore Juan Miguel Artigas Azas

If you just keep an isolated breeding pair, something else has to be taken into consideration: the pair bond may not be as stable as you think. Talking to people at conventions I just too often hear that a well-matched pair which has been kept for several years peacefully together in an aquarium turned on each other for no apparent reason, and the female was killed. A pair bond may break for several reasons, most noticeable after a failed spawn where the male demands the unprepared female to spawn again right away, or else.

If you try to use the large number method please consider that you cannot add more individuals of a species to an already established colony without putting them in big danger to be attacked by the settlers. Remember that fish protecting a territory are normally strongly motivated and may beat even larger specimens. Before you add new individuals to an aquarium make sure to sufficiently change the landscape so all existing territory boundary markers are lost and a new order must be established. Introducing new fish after a water change and just before dark is then the best approach in my experience.

So after all, it is possible to keep a fish room where the aggressive cichlids that you host are able to live in relative peace and transfer that peace of mind and enjoyment to you as an aquarist. I hope this article may help you develop or improve you cichlid husbandry techniques and enjoy the results.

Referenze (1):


Artigas Azas, Juan Miguel. (giugno 24, 2020). "Managing cichlid aggression in closed spaces". Cichlid Room Companion. URL consultato in data aprile 11, 2021, da: