As above, with your tank size you have a wide variety of species to choose from. Lake Malawi cichlids are broken down into 3 groups.
1.
Mbuna, literally means rock-dwelling. They typically range in size from 3" - 5" though there are a couple of species that reach 7". They range from mildly aggressive to incredibly psychotic, so careful stocking is in order, they are generally overstocked so that any weaker fish get "lost in the crowd". They are harem breeders where one male will mate with as many females as possible, so ratios of 1m for every 3 or more females is usually recommended, with the more aggressive species such as any of the
Melanochromis, ratios of 1m/5f is best.
Pseudotropheus demasoni is the exception, the are so highly aggressive toward their own speices or similar looking ones that they should be kept in groups of 12+. Nearly all mbuna are herbivores and will succumb to disease if fed a predominately "meaty" diet, however, most of the
Cynotilapia species and
L.caeruleus are omnivores and can be mixed with haps/peacocks.
2.
Peacocks, any of the
Aulonocara species, they are called peacocks due to the brightly colored males, females of all species are typically a dull brown/gray color. Peacocks are far less aggressive than mbuna, though they could still be considered semi-aggressive by community standards. The biggest problem with this group is their tendency to hybridize, that and the man made "species" found in the market. They are carnivores and can be mixed with the less aggressive hap species as well as
L.caeruleus of the mbuna group. Peacocks generally reach 5" - 7".
3.
Haps - basically all the leftover cichlid species of Lake Malawi, the majority of them are open water predators. They range from peaceful to highly aggressive and the vast majority are carnivores, though there are some herbivorous species. They range in size from 3" to over 1.5ft! They typically prefer open space in their tanks with minimal decorations as they are fast powerful swimmers. They don't mix well with mbuna partly due to their differing dietary needs, but also because when small the haps are terrorized by the mbuna but once they reach their full size (if not killed) they will turn the tables by picking off the mbuna. Not to say it hasn't been done successfully, but it is a very fine balancing act.
Unfortunately I'm not the one to give you adivce about Lake Tanganikya species, but hopefully some of our members that do keep them will add their thoughts.
And here's a link to some mbuna articles worth reading if they interest you:
http
/www.fishforums.net/index.php?/topic/314138-all-about-mbuna/
