An Article by Francesco Zezza & George J. Reclos
The purpose of this article is to give you an insight into the behavior of the most common tankmate of African cichlids : catfishes. Being it a Plecostomus sp., an exotic Scobiancistrus or a Synodontis species, catfishes share some things in common. When placed in an African cichlid tank with the correct (for the cichlids) water parameters, some of them feel like at home (Synodontis sp.) while others have to adapt a bit, especially those coming from the acidic, soft water of the Amazon basin. Most of them are nocturnal fish and most hobbyists just expect them to clean the glass of the aquarium from algae. That's about all an average African cichlid addict knows about them - and he doesn't really care to know more. Wrong. Those fishes are beautiful, very interesting and can add to the overall look of the tank. Francesco has already given some information in his very interesting article, the pleco connection. As you can read there, catfishes are not "decoration" objects, on the contrary (not to mention that some of them are more expensive and rare than our cichlids).
One of the issues that needs to be further addressed is their territorial nature and their ability to exert aggression not only against other catfishes but also other species if provoked. Of course this is not the case with very small members like Corydoras but larger specimens do not hesitate to attack and even chase fully grown up African cichlids around a large tank. What's more, they don't seem to forget easily. I have repeatedly seen my large (25 cm) Glycopterichthys gibbiceps resting on a rock and suddenly, when the right fish come close, start chasing it again. There is more than that, since large catfishes (especially suckermouths) can cause severe wounds on cichlids especially at night. You can read more about it in the relevant article "plecos and African cichlids".
However, this aggression and territorially behavior is far more evident between catfishes. This can be observed either between members of the same species or between different species. It is said that once you see a serious fight (even a bloody one) between catfishes you will immediately classify your mbuna as "peaceful, community fish".
My experience with aggression directed against conspecifics include the endless chasing of my two Botia modesta or the homeric fights of the two Glycopterichtys gibbiceps. Please note that another (extremely) territorial and aggressive fish (although mainly against members of its own species) is one of the best scavengers for African cichlid tanks, Akanthopsis Choerorhynchus (horse-face loach). It is practically impossible to have two survivors in anything smaller than a 500 liter tank. My "dominant" horse face loach clearly showed me the right signs from the very first day. A week later the second one was lying dead. When I started my 1300 liter tank I added three of them - thinking it was big enough. Wrong again.. One of them was found dead a month later. Two years later, I was happy to see the remaining two loaches (although 1.5 meters apart) after the lights went off.
As far as aggression between different species is concerned, we don't need to go that far.. A classic is the various species of Synodontis. I know of various setups which contain only one Synodontis species. The happy owners only see it after feeding and are absolutely convinced that this is a shy, peaceful species. If you try to introduce a second Synodontis of the same species in that tank, you will be surprised to find out that the tank in which were keeping 50 mbuna without any problem is simply too small for two Synos. It is true that more often than not, what happens in one tank will not happen in another. Therefore the observations I make may or may not apply in your tank. However, I have come to understand is that my four (different) Synodontis species have formed two "pairs". Synodontis decorus vs. S. notatus and on the other hand Synodontis angelicus vs. S. ocellifer.
During one of the usual fights between my two G.gibbiceps I was lucky to have my camera ready.. Since the fight went on for more than half an hour there was no need to hurry.. but better safe than sorry.
Catfishes use different "dogfight" techniques but the result is the same.
See next page for more..