Mixing Old World and New World cichlids is about more than just water chemistry.
Paul V. Loiselle
Q. I have an 80-gallon aquarium with a mixture of full-grown African and South American cichlid fish. I have heard that these two cichlid fish groups do not get along well together, yet I have no problems. My question is simple: Can African and South American cichlid fish live peacefully in the same aquarium for a long period of time or should I expect a battle?
A. It all depends on which African and South American cichlid fish you are maintaining! Regrettably, the categories of "African cichlid" and "South American cichlid" do not mean the same thing to hobbyists and to ichthyologists. For the majority of aquarists, African cichlid is synonymous with "Lake Malawi cichlid," while South American cichlid means any species native to the New World tropics, and as such is as likely to be applied to a firemouth cichlid as to a keyhole cichlid.
This is not merely a question of technical nit-picking. Lake Malawi is a very different environment than the rivers of West and Central Africa — an observation also legitimately made for aquatic habitats in South and Central America. The hard alkaline water that Lake Malawi cichlids must have to prosper is not appreciated by such Amazonian cichlids as the uaru or the many different acaras and eartheaters native to that part of South America.
On the other hand, West African riverine cichlids adapt well to the water conditions Amazonian cichlids demand for survival. Insofar as compatibility is a function of shared environmental requirements, one could reasonably expect such West African dwarf cichlids as Anomalochromis thomasi and the various Pelvicachromis species to manage quite well in the company of such neotropical dwarves as the smiling acaras of the genus Laetacara and the numerous Apistogramma species. I have kept West African and South American cichlids together many times, and representatives of each group have bred successfully in the presence of the other — proof of the viability of such cohabitation.
Water conditions in most of Middle America display a high degree of seasonal variability. Hard, alkaline water conditions tend to be the rule during the dry season, so it's no surprise that Middle American cichlids are better able to cope with the conditions prevailing in a Lake Malawi community aquarium than are their distant South American cousins. Behavioral compatibility, however, is another issue.
The cichlids of Lake Malawi and Middle America have very different reproductive patterns. With the exception of Tilapia rendalli, a widely distributed riverine species, all Lake Malawi cichlids are polygamous maternal mouthbrooders. In this sort of mating system, territorial behavior is restricted to males, parental behavior to females. The area defended is restricted to the actual spawning site, and defense is only for a short period up to and during the actual spawning act, targeted primarily at other males of the same species.
The cichlids of Middle America, as well as many of their South American cousins, have a monogamous mating system and the long-term care by both parents of the mobile young. Both sexes participate in the defense of an area that extends well beyond the actual spawning site, and will eventually comprise a substantial volume of space surrounding a school of mobile fry. Site defense can start up to two weeks prior to spawning, and aggressive defense of the mobile fry may persist for up to eight weeks, targeted at any fish large enough to pose a threat to the pair's progeny.
Assuming that representatives of each group include both males and females of the same species, attempting to house cichlids that differ so markedly in their approach to territorial defense is asking for trouble. Faced with such poor odds, a male Malawi cichlid stands little chance of establishing a breeding territory in such a setting, and runs the risk of injury should he attempt to do so.
If this were not problem enough, individuals of both sexes eventually have to cope with the unrelenting attacks of their parental neotropical tankmates. In an aquarium of 125 gallons or more, such hostility may not always result in physical damage, but the ongoing aggression of parental tankmates still represents major environmental stress, which, in turn, increases its victims' susceptibility to disease.
This state of affairs is much less apt to arise in a community of solitary specimens. Although your letter provides no details regarding this, the fact that you have not, to date, encountered problems suggests such an arrangement. If so, relative harmony should prevail as long as the makeup of your community precludes any attempt at breeding.